Atmospheric Insights: July 2006

Saturday, July 29, 2006

The Rise and Fall of AAM

The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).

http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf

From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.

Global tropical SSTs remain generally above normal, especially from the South American west coast at ~20S extending northward to the equatorial cold tongue then on to the date line. SSTAs ~ plus .5-1.5C to at least depths of 100-150m were being observed in those regions per the latest TAO array data (link below). The latter may be partly from the seasonal cycle since SST climatology favors cooling in this region, and perhaps from an earlier very weak Oceanic Kelvin wave currently reaching the South American coast. Latest TAO buoy data continues to observe surface westerly wind anomalies (~ 5m/s) and even actual westerlies along the equator from about 160W to west of the date line, with evidence of another downwelling oceanic Kelvin wave crossing into the Western Hemisphere. Actual SSTs in excess of 29C still dominate from the South Pacific into the Indian Ocean, and nearly all of the Tropical Northwest Pacific. In fact, there has even been some warming during the past week-10 days, especially across the tropical Atlantic Ocean. Additional global SST information can be obtained from latest TAO data here, ESRL/PSD data here, CPC data

http://www.cpc.ncep.noaa.gov/products/predictions/threats/index_gloss.html,

and BMRC at

http://www.bom.gov.au/bmrc/ocean/results/climocan.htm .

From continuous monitoring and various diagnostic and dynamical tools, there is growing evidence, to me, that the weather-climate system is tilting toward a warm event. In fact, a weak warm event may already be underway. However, the magnitude of any possible warm event and global impacts are unclear. The following are links to ENSO discussions.

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html

Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.

http://www.cpc.ncep.noaa.gov/products/predictions/90day/

Coherent signals of tropical convective forcing are still hard to come by. The MJO signal has been essentially non-existent since about March (there is a climatology component to this), and the 20-30 day variability occurring since at least December 2005 (see ESRL/PSD weather-climate discussions) has weakened. Nevertheless, per coherent modes Hovmollers and other combined plots and animations, a case can be made of a weak convectively coupled dynamical signal having returned to the Eastern Hemisphere starting roughly 10-14 days ago. Loosely, this may be a mixed mode consisting of a convectively coupled Kelvin wave and forcing from Southern Hemisphere dynamics. The flare-up observed in the central equatorial Indian Ocean about a week-10 days ago was tied to this process, and has since lead to a rapid eruption of thunderstorm clusters from India through the Bay of Bengal and portions of Southeast Asia (northern tropics). OLRA have been ~minus 50-70 W/m**2 in these areas. This region of thunderstorm activity appears to be drifting east at around 9 m/s (roughly 10 deg long/day) per a “back of the envelop” calculation.

Tropical convection also persists from Southeast Asia toward the equatorial date line, forced by the warm SSTs (see http://www.npmoc.navy.mil/jtwc.html for details of tropical cyclones). I would expect this region of tropical forcing across the Tropical Northwest Pacific (TNWP) to intensify during the next couple of weeks as the region farther west consolidates with this thunderstorm activity (monsoon systems understood, which have been active this year). Should that occur, tropical cyclone activity may increase and threaten locations such as the Philippines, Southeast Asia and possibly Japan.

Any dynamical signal supporting tropical convection across the Western Hemisphere is weak. However, based on near equatorial 200mb velocity potential Hovmollers, there is a suggestion upper tropospheric divergence has stalled around Central America since about July 10th. Satellite imagery (7/29) shows enhanced clusters of thunderstorms from the Amazon Rain Forest into most of Central America and adjacent areas of the eastern Pacific and western Caribbean. In fact, there is moisture transport from this region into the southwest and south central USA as I type. I could even offer there are weak twin subtropical anticyclones tied to this activity leading to subtropical jets (STJs) including one affecting the Pacific Northwest (see links to animations below). A point I will again offer is there may be a dynamical relationship between this Western Hemisphere tropical forcing and the activity west of the date line. The details are unclear, and any speculation I offer cannot be done here (SSTs are one component, roles of the Hadley and Walker Cells are other scientific matters).

Empirical, statistical and numerical prediction tools continue to be inconclusive for useful information about the future evolution of the tropical convection. Please see ESRL/PSD MJO tools , BMRC MJO tools, CPC MJO tools, and http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html for the details (and draw your own conclusions). These tools generally rely on a moderate to strong MJO signal, which is nearly non-existent at this time. My own thoughts have already been offered.

Time-latitude sections of 200mb zonal mean zonal wind anomalies show there has been some collapse of westerly flow throughout the tropical and subtropical atmospheres, with even zonal mean anomalous easterly flow of ~ 5m/s present at 30N. In fact, on about July 10th there was above average westerly flow present throughout the subtropical North Pacific, replaced by easterlies by around July 26th. I can ascribe this change to the tropical convective flare-up across the central equatorial Indian Ocean discussed above and an earlier wave energy dispersion from a large anticyclone that was over the Tibetan Plateau occurring from ~15-22 July (see animations). The latter was part of a ~50 day mountain-frictional torque index cycle (interacting with the SST boundary forced TNWP convection) discussed in past postings, and this did contribute to recent deadly “heat wave ridge” across western North America.

Tropospheric global relative AAM is about normal based on the 1968-1997 reanalysis climatology through July 26th. However, the global (remember) mountain and frictional torques are ~ minus 5 and minus 15 Hadleys, respectively (a lot coming, again, from the Southern Hemisphere), and the global AAM tendency is ~minus 25-30 Hadleys. The latter is coming from particularly the Andes Mountains as well as the deep tropics. I do think we are going into a negative “phase” of our mountain-frictional torque index cycle, and I am not sure how that will force the circulation in the presence of the already discussed tropical convective forcing including the possible emergence of a warm event (El-Nino). Incidentally, the operational AAM plot based on the 1979-1998 climatology has the global integral at ~ minus 1 sigma, since there are 2 strong and 2 moderate El-Ninos in that shorter climatology.

The tropical convective flare-up that started roughly a week-10 days ago across the equatorial Indian Ocean progressed into the Bay of Bengal about the middle of last week (~July 27th). As shown by animations of 150mb and 250mb daily mean vector wind anomalies, a fast wave energy dispersion passing through the Asian subtropics (subtropical wave train) interacted with this flare-up and led to arguably a rapid Rossby wave energy dispersion (RWD) event across the Pacific Rim. In some sense the result has been a discontinuous retrogression of the “hot western USA ridge” to ~150-160W, with an anomalous anticyclonic gyre near 50N/160W having 250mb wind speed anomalies ~50-60 m/s on July 28th. An anomalous trough is digging just off the Pacific Northwest Coast as I type, and will give folks in that part of the country relief from the heat for at least week 1.

Since AAM tendency is at a negative minimum along with the negative torques discussed above, I think GSDM Stage 4 best describes the current weather-climate situation. The distribution of the Eastern Hemisphere tropical convective forcing also lends some support to that notion. However, there is literally no MJO, and other signals are weak. As discussed below, in this type of situation almost "anything can pop out".

GSDM Stage 4 was not an option I offered in my last writing on this Blog (July 22nd). In fact, I suggested going from GSDM Stage 2-3 may occur at this time, meaning, globally, we would add westerly flow instead of removing it, like we are right now. This just shows how good I am with offering predictive insights at times, and anyone who makes predictions needs to recognize the limitations (whatever the time/space scales). As I have preached before, any predictive information must be done with statistically useful scientifically defensible statements of probability (and the proper resources, support and commitment/discipline).

For weeks 1-3, I think we are dealing with a weather-climate system where a warm event may be emerging, faster modes of tropical convective variability may continue, our mountain/frictional torque index cycle seems to be continuing, all interacting with fast extratropical wave energy dispersion processes. My suspicion is the tropical convective forcing across the west central and northwest Pacific may become dominate during weeks 2-3. However, uncertainty is very high after week 1. Good model agreement offers some confidence for week 1.

Week 1 (30 July – 5 August 2006): GSDM Stage 4-1 is most probable. Synoptically we should see a trough across the western USA with a Southeast states ridge. Cooler weather is likely for much of the Pacific Northwest-California through the Northern Rockies while the central and eastern USA have potentially deadly heat/humidity. An active severe local storm/MCS track is likely from the Northern/Central Rockies into the Upper Mississippi Valley/Great Lakes through about the middle of this period. This track should shift southeast as the cooler air does the same. The Southeast into the Mid Atlantic states are likely to stay very warm this whole period. Other types of weather should be apparent in this kind of active pattern. There may be a window of opportunity for some kind of North Atlantic tropical cyclone development during this period going into week 2. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.

Week 2 (6-12 August 2006): A transition to GSDM Stage 2 may occur, suggesting the trough would shift toward the central USA while ridge amplification occurs from around/just off the west coast into Alaska. Synoptically there may be a deep trough from Hudson’s Bay into the Northern Plains (~90-100W) with a Southeast states ridge. This would suggest cool/wet for the Central and North Central states, warm/wet for much of the East and warm/dry for the West and Pacific Northwest. An eastward shift of this pattern would return the heat into the western part of the country.

Week 3 (13-19 August 2006): Unclear. During August 2004, before the 2004-05 warm event, GSDM Stage 2 was quite robust (please see our weather-climate discussions). Are we going to see that again???

A welcome cool down seems like a good bet for Southwest Kansas by the middle of next week (~ Wednesday) after a few days of maxes ~100-108F. Highs may lower into the upper 70s-80s for especially Wednesday, with a warm up into the 90s by next weekend. I would also like to think there should be a few opportunities for storms and rainfall beginning Tuesday night through Friday. For week 2, if a situation similar to August 2004 returns, that would be good news for additional rainfall and relatively cooler temperatures. We will have to see. In any event, whatever the details I would think rainfall should be near normal weeks 2-3.

The time -filtered coherent modes Hovmoller plots of OLR and OLRA are at http://www.cdc.noaa.gov/map/clim/olr_modes/), velocity potential Hovmollers at http://www.cpc.ncep.noaa.gov/products/intraseasonal/vpot_tlon.html , and an animation of velocity potential overlayed on OLRAs are at http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ir_anim_monthly.shtml.

Satellite imagery and other information can be found from the following links: eastern hemisphere, full-disk west Pacific, mtsat, IO, Africa, http://www.jma.go.jp/en/gms/ ; other imagery here. Latest tropical cyclone statements can be found from http://www.nhc.noaa.gov/, while the latest 3-day averages of OLR totals and anomalies and other data can be found here
http://www.cdc.noaa.gov/map/clim/glbcir.anim.shtml (animations of various fields from the operational data)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml (Global Tropical Hazards Assessment available from this site, along with other useful information)

http://www.cdc.noaa.gov/map/clim/aam.rean.shtml (reanalysis AAM plots)

http://www.cdc.noaa.gov/map/clim/aam.shtml (operational AAM plots)

Latest CDC Ensemble Forecast

Latest NCEP Ensemble Forecast

Additional NCEP Ensemble Output

Latest Canadian Ensemble Output

Latest Deterministic ECMWF Forecasts

http://www.cdc.noaa.gov/people/jeffrey.s.whitaker/refcst/week2/

http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html (link to our Weather-
Climate discussions)

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html (model performance; please navigate to others)

Please see the CPC Drought Monitor for areas of dryness and the latest official outlooks and statements from the Storm Prediction Center not only for severe storms, but also fire weather concerns. Finally, the CPC USA Hazards Assessment for offers additional insights not only for possible week 1 high impact weather, but week 2 as well.

I will try to do another posting on about the middle of next week. Work is also on-going to post a weather-climate discussion on the ESRL/PSD MJO web site hopefully by about the middle of August (pushed back).

Ed Berry

Wednesday, July 26, 2006

Update Postponed

Because of internet connectivity problems and time spent on work for the next posting of a weather-climate discussion for the ESRL/PSD MJO web site, I was unable to do an update this afternoon. I apologize, and hope to post at least a short writing this coming weekend.

Thank you,
Ed Berry

Saturday, July 22, 2006

Balance of Momentum

The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).

http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf

From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.

SST anomalies across the extreme eastern equatorial Pacific remain ~plus 1C, with somewhat larger anomalies extending downward to nearly 100m. The latter may be partly from the seasonal cycle since SST climatology favors cooling in this region, and perhaps from an earlier very weak Oceanic Kelvin wave currently reaching the South American coast. Above average SSTs dominate the eastern Pacific Ocean equatorial cold tongue all the way to the date line, extending at depth to ~200m (deeper than normal thermocline). Latest TAO buoy data still shows surface westerly wind anomalies (~ 5m/s) and even actual westerlies along the equator west of the date line. Deepening of the 20C isotherm suggests evidence of another downwelling oceanic Kelvin wave crossing into the Western Hemisphere. Actual SSTs in excess of 29C still dominate from the South Pacific into the Indian Ocean, and nearly all of the Tropical Northwest Pacific. Additional global SST information can be obtained from latest TAO data here, ESRL/PSD data here, CPC data

http://www.cpc.ncep.noaa.gov/products/predictions/threats/index_gloss.html,

and BMRC at
http://www.bom.gov.au/bmrc/ocean/results/climocan.htm .

From continuous monitoring and various diagnostic and dynamical tools, there is some evidence the weather-climate system is tilting toward a warm event. However, the magnitude of any possible warm event and global impacts are unclear (some additional discussion below). The following are links to ENSO discussions (recently updated).

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html

Please also see the following CPC link (and others therein) for further ENSO, etc., insights.

http://www.cpc.ncep.noaa.gov/products/predictions/90day/

Coherent signals of tropical convective forcing remain very weak. There has been a loose consolidation deep convection ~10-15N/120-140E during the last few days, while the monsoon system remains active from India into Southeast Asia. Possibly linked to jet streak dynamics with the Southern Hemisphere, yet another small convective flare-up has occurred across the central equatorial Indian Ocean. Three-day averaged OLRA with this activity has been ~minus 50 W/m**2. If I am monitoring correctly, this is the third such kind of event this month, which is much more frequent than observed since the start of 2006. Tropical convection has also increased nicely across the African Sahel during the past week. Attribution to the latter is still unclear (one can always speculate). Finally, enhancement of tropical convective forcing remains from the East Pacific into Northern South America, with 3-day averaged OLRA ~minus 30-50 W/m**2. Category 4 (at least) Hurricane Daniel and recently developed Tropical Storm Emilia continue across the East Pacific (please see http://www.nhc.noaa.gov/ for details).

Since I went into some length about the possible modes of variability with the tropical forcing during my last writing, I will not repeat all that here. The Wheeler Phase Space Diagram shows a weak projection onto a MJO from the Western Hemisphere into Africa (links below). However, with tropical forcing signals so weak right now, almost anything can suddenly “pop out”. I do not think there is any true MJO signal at this time, and feel there has not been even a weak one since March 2006.

I am suspicious the slow feedback processes between the SSTs, convection and atmospheric response may be growing and expanding. There may now also be coupling between the moist convection and warm SSTs starting to occur with the East Pacific SSTs, as well. If this is true, that may have been initiated by processes still going on across the Tropical Northwest Pacific (coupling) including the weak oceanic Kelvin waves warming the East Pacific equatorial cold tongue in proper phase with the seasonal cycle. Of course, the enhanced East Pacific tropical convective forcing is well north of the cold tongue (need SSTs ~ >=29C to sustain the storm clusters). I suspect other processes involving the northern extratropics working with the Tropical West Pacific convection started a warming of the north tropical (~5-15N) East Pacific earlier this year (~March; we need to remember the western Pacific convection has been shifting north with the seasonal cycle). The point is these are very complicated dynamical processes which only someone who monitors these things daily may be able to detect. To me, I think it is plausible to propose that the tropical western and eastern Pacific Ocean basins are feeding back off of each other through a complex forcing-response-feedback scenario which cannot be described here. I can physically see how this could further enhance the already slightly above average SSTs from west of the date line to the coast of South America during the coming months (a warm event?). However, this is pure (but I felt useful) speculation on my part, and let us see what happens. Please see http://www.npmoc.navy.mil/jtwc.html for details of the western Pacific tropical cyclones.

Empirical, statistical and numerical prediction tools continue to be inconclusive for useful information about the future evolution of the tropical convection. Please see ESRL/PSD MJO tools , BMRC MJO tools, CPC MJO tools, and http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html for the details (and draw your own conclusions). These tools generally rely on a moderate to strong MJO signal, which is nearly non-existent at this time, per above.

Again, relationships I discussed in my last Blog posting between the mountain-frictional torque index cycle and the 20-30 day tropical convective variability still apply (for now), and will not be repeated. Time-latitude sections of 200mb zonal mean anomalies show anomalous westerly flow is once again slowly increasing throughout the tropical and subtropical atmospheres. Zonal mean westerly anomalies are ~5-10 m/s from about 25N-30S, with the largest magnitudes south of the equator. This has contributed to a positive AAM tendency ~20 Hadleys as of July 19th per reanalysis data, and actual relative tropospheric AAM is increasing (as would be expected).

Tropospheric global relative AAM is near average per the 1968-1997 reanalysis climatology based on data through July 19th. The more recently updated operational data relative AAM plot shows values to have dipped to ~1 sigma below normal based on a 1979-1998 climatology which includes 2 strong and 2 moderate warm events (El-Ninos). I would think tropospheric relative AAM would return to above average (at least for the reanalysis climatology) during the next week or so. In addition to the character of the tropical convective forcing discussed above, the global mountain torque is also increasing (much of the contribution from the tropics including the Andes) and that component will also increase the westerly flow.

The global frictional torque is actually returning to ~ minus 10 Hadleys, with much of that contribution coming from the Southern Hemisphere extratropics (austral winter). Now comes trying to understand the Earth-Atmosphere AAM budget given the tropical convective forcing issues already discussed above and the other matters given attention in the July 19th posting. I can physically see why there are a lot of low pressure/strong baroclinic extratropical storms across the Southern Hemisphere extratropics, leading to the negative frictional torque, as a response to all the feedbacks. As long as the tropical convection and north-south mountain ranges keep adding westerly flow to the atmosphere, eddy feedback processes such as “strong low pressure areas” in the Southern Hemisphere will be needed to maintain AAM balance.

Animations of daily mean anomalies of 150mb and 250mb vector winds present fairly clean fast wave energy dispersions interacting with generally persistent twin subtropical anticyclones ~150E. The anticyclonic gyre ~35N/105E referred to in the previous posting has contributed to a well-defined baroclinic wave packet helping to amplify the current ridge across western North America. It is also apparent there is a large meridional character to the extratropical flow across both hemispheres with some symmetry. GSDM Stage 2 best describes the global weather-climate situation.

Uncertainty remains extremely high. Since I want to keep this posting from not getting much longer, the “bottom line” is I do think a transition to GSDM Stage 3 is a useful offering during weeks 1-3. However, I cannot offer anything about timing and synoptic details. More and more ensemble numerical models show the western North American ridge deamplifying and moving east while a trough develops along the West Coast. Additionally, the polar jet stream westerlies are predicted to increase along the US/Canadian border, all during week 2.

Week 1 (23-29 July 2006): GSDM Stage 2 continuing is most probable. The intense heat from the western USA should start to shift into the Plains during this period, while at least seasonal weather continues for the eastern states. Severe local storms/MCS may be a concern from the Central/Northern Plains into the Ohio Valley. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.

Week 2 (30 July - 5 August 2006): GSDM Stage 3 may return, meaning much of the USA may have weather similar to what was observed from ~13-20 July. That is, intense heat may affect a large part of the country once again.

Week 3 (6-12 August 2006): GSDM Stage 3 may persist.

I am concerned the hot weather with maxes above 100F may return to Southwest Kansas as early as Tuesday (7/25), but more likely starting next weekend into at least week 2. At least a few rounds of scattered storms are probable week 1 before the “real heat” starts.

The time -filtered coherent modes Hovmoller plots of OLR and OLRA are at http://www.cdc.noaa.gov/map/clim/olr_modes/), velocity potential Hovmollers at http://www.cpc.ncep.noaa.gov/products/intraseasonal/vpot_tlon.html , and an animation of velocity potential overlayed on OLRAs are at http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ir_anim_monthly.shtml.

Satellite imagery and other information can be found from the following links: eastern hemisphere, full-disk west Pacific, mtsat, IO, Africa, http://www.jma.go.jp/en/gms/ ; other imagery here. Latest tropical cyclone statements can be found from http://www.nhc.noaa.gov/, while the latest 3-day averages of OLR totals and anomalies and other data can be found here
http://www.cdc.noaa.gov/map/clim/glbcir.anim.shtml (animations of various fields from the operational data)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml (Global Tropical Hazards Assessment available from this site, along with other useful information)

http://www.cdc.noaa.gov/map/clim/aam.rean.shtml (reanalysis AAM plots)

http://www.cdc.noaa.gov/map/clim/aam.shtml (operational AAM plots)

Latest CDC Ensemble Forecast

Latest NCEP Ensemble Forecast

Additional NCEP Ensemble Output

Latest Canadian Ensemble Output

Latest Deterministic ECMWF Forecasts

http://www.cdc.noaa.gov/people/jeffrey.s.whitaker/refcst/week2/

http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html (link to our Weather-
Climate discussions)

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html (model performance; please navigate to others)

Please see the CPC Drought Monitor for areas of dryness and the latest official outlooks and statements from the Storm Prediction Center not only for severe storms, but also fire weather concerns. Finally, the CPC USA Hazards Assessment for offers additional insights not only for possible week 1 high impact weather, but week 2 as well.

I will try to do another posting about the middle of next week. Work is also on-going to post a weather-climate discussion on the ESRL/PSD MJO web site hopefully by early August.

Ed Berry

Wednesday, July 19, 2006

The Earth Giveth..........

The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).

http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf

From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.

There has not been much change to the global tropical SSTs during the past week. However, SST anomalies across the extreme eastern equatorial Pacific have rapidly increased to ~plus 1.5C, with somewhat larger anomalies extending downward to nearly 100m. The latter may be partly from the seasonal cycle since SST climatology favors cooling in this region, and perhaps from the very weak Oceanic Kelvin wave initiated ~2 months ago finally reaching the South American coast. In any case, above average SSTs dominate the eastern Pacific Ocean equatorial cold tongue all the way to the date line, extending at depth to ~200m (deeper than normal thermocline). Latest TAO buoy data still shows surface westerly wind anomalies (~ 5m/s) and even actual westerlies along the equator from the date line and west, with evidence of a downwelling oceanic Kelvin wave crossing into the Western Hemisphere. Actual SSTs in excess of 29C still dominate from the South Pacific into the Indian Ocean, and nearly all of the Tropical Northwest Pacific.

Additional global SST information can be obtained from latest TAO data here, ESRL/PSD data here, CPC data

http://www.cpc.ncep.noaa.gov/products/predictions/threats/index_gloss.html,

and BMRC at

http://www.bom.gov.au/bmrc/ocean/results/climocan.htm .

From continuous monitoring and various diagnostic and dynamical tools, there is some evidence the weather-climate system is tilting toward a warm event. However, the magnitude of any possible warm event and global impacts are unclear. The following are links to ENSO discussions (recently updated).

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html

Please also see the following CPC link (and others therein) for further ENSO, etc., insights.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/

Coherent signals of tropical convective forcing have been hard to come by recently. The MJO signal has been essentially non-existent since about March (there is a climatology component to this), while 20-30 day variability has been occurring since at least December 2005 (see ESRL/PSD weather-climate discussions). The latter have exhibited faster eastward propagation including convectively coupled Kelvin waves. Starting early May, northward propagation to the 20-30 day modes started (seasonal cycle), particularly from the equatorial Indian Ocean into the Indian and Southeast Asian Monsoon systems. About a week ago, the third of these events appeared across the central equatorial Indian Ocean. There has not been much movement; however, latest 3-day averages of OLR indicate anomalies have decreased to ~minus 50-70 W/m**2. Finally, the monsoon system enhanced rainfall continues from the Bay of Bengal into Southeast Asia and the Philippines, which is a bit east of normal.

Tropical convection persists across the west central and northwest Pacific, with episodes of tropical cyclone development (see http://www.npmoc.navy.mil/jtwc.html for details). This region of enhanced SST boundary tropical thunderstorm activity has continued for nearly 2 months, slowly drifting northwest with the seasonal cycle while having intensity variations from the 20-30 day modes per above. At least 2-3 equatorial surface westerly wind events have come out to the date line with this activity. Given the recent increase in the intensity of the equatorial Indian Ocean rainfall, I would expect another convectively coupled Kelvin wave to enhance the SST boundary forced convection farther east during the next couple of weeks. In fact, full disk satellite imagery already suggests a very loose consolidation of the Eastern Hemisphere tropical convective forcing, extending from the central Indian Ocean into the Tropical Northwest Pacific with the monsoon rainfall on the northern portion of that envelope. A convectively coupled Kelvin wave may be emerging into the western Pacific, and the time filtered coherent modes Hovmollers lend some support to that notion.

Any dynamical signal supporting tropical convection across the Western Hemisphere has become weak and incoherent (based on 200mb velocity potential and other fields). There is some enhancement from the northward displaced eastern Pacific ITCZ (including Hurricane Daniel – links below) into the southwest Caribbean and more recently central Africa.

Empirical, statistical and numerical prediction tools continue to be inconclusive for useful information about the future evolution of the tropical convection. Please see ESRL/PSD MJO tools , BMRC MJO tools, CPC MJO tools, and http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html for the details (and draw your own conclusions). These tools generally rely on a moderate to strong MJO signal, which is nearly non-existent at this time. My thought would be for the enhanced Tropical Northwest Pacific convection to possibly dominate the tropical forcing during the next couple of weeks, while a somewhat eastward shifted Indian and Southeast Asian monsoon persists. The latter may be enhanced as “Indian Ocean event number 3” propagates northeast. The future evolution and roles of the east Pacific ITCZ and especially African convection is unclear.

Time-latitude sections of 200mb zonal mean zonal wind anomalies still indicate most of the tropical and subtropical atmospheres to be dominated by westerlies. However, magnitudes are only ~5m/s compared to at least 10m/s a couple of weeks ago. Weak easterly wind anomalies have even returned to the midlatitudes of both hemispheres. The latter is a contributing to the expected week 1 retrogression of synoptic features across the Pacific-North American sector (more said below).

Poleward and downward propagation of zonal mean wind anomalies continue. The most recent round of westerly anomalies to propagate out of the equatorial and subtropical atmospheres has reached the Earth’s surface across the midlatitudes (loosely speaking). This has contributed to negative mountain and frictional torques (frictional torque leads by ~6 days), removing some of the anomalous vertically averaged zonal mean westerly flow (with the Southern Hemisphere doing much of the work, as would be expected). In other words, the Earth is taking away AAM from the atmosphere, after giving AAM to it about 3-4 weeks ago (giveith, and now takeith away!).

A much more complete understanding of the poleward propagation of circulation anomalies and forcing-response-feedback relationships requires a vertical average of zonal mean anomalies and a global summation (regional considerations and other dynamical processes understood). This is one reason to make use of the atmospheric angular momentum (AAM) plots from ESRL/PSD (links below). Yes, this is a restatement from a week ago, but I think it is worthwhile, and needed.

Tropospheric global relative AAM is still ~1 sigma above the 1968-1997 reanalysis climatology based on data through July 14th. The more recently updated operational data relative AAM plot shows values to have dipped slightly below normal based on a 1979-1998 climatology which includes 2 strong and 2 moderate warm events (El-Ninos). Through July 14th the mountain and frictional torques were returning to normal (still ~ minus 5 Hadleys) while the tendency was ~minus 30 Hadleys.

A very important point that we hope to demonstrate in our next weather-climate discussion is the roughly clean 40-50 day variation of vertically averaged zonal mean wind anomalies throughout the tropical and subtropical atmospheres observed since at least mid April. This variation has been nicely observed in the global integral of relative AAM, with strong contributions coming from both the mountain and frictional torques. For instance, during much of May we observed reduced trades (lead to a negative frictional torque), followed by enhanced trades during June (positive frictional torque which adds westerly flow to the atmosphere), then a recent reduction. The positive June global frictional torque was followed by a positive global mountain torque by late June, with a collapse afterwards (see links). During these poleward propagating events there is this constant exchange of AAM between these torques, adding and removing westerly flow from the atmosphere (part of the Earth-Atmosphere AAM budget). The most recent addition of westerly flow to the atmosphere (mainly June) contributed to the current heat wave that both much of the USA and Europe are experiencing. Now, both torques are reducing AAM, contributing to the negative AAM tendency. In our GSDM, we refer to this component as a “mountain-frictional torque index cycle”.

The mountain-frictional torque index cycle has been going on in the presence of the 20-30 day tropical convective variability and SST boundary forced convection across the Tropical Northwest Pacific (monsoon systems understood). Finally, fast Rossby wave energy dispersions have occurred with these other dynamical processes. So, even though the MJO signal has been essentially “not there” since at least March, at least 3 other components as described by the GSDM have been present, but still with a WEAK overall signal. In a sense, the stationary boundary forced convection can be thought of as a “stationary MJO” within the context of the GSDM (thus all 4 components).

In my postings during the last couple of weeks, I have offered that the anomalous global and zonal mean westerly flow throughout the atmosphere would collapse. I was basing that on the SST boundary forced western Pacific convection and attempting to time the 20-30 day mode. Loosely, my feeling was there would be a transition from what has recently been GSDM Stage 3 to Stage 2. This process is occurring as I type. However, and very important, I was not totally in tune with the mountain-frictional torque index cycle already discussed, which is very hard to do since it is a stochastic process. Also, there is no way myself or anyone will know the synoptic details of these kinds of interactions beyond days 2-3 (generally). The point is we can only offer defensible predictive information making use of probability statements.

Animations of daily mean anomalies of 150mb and 250mb vector winds continue to show twin somewhat distorted subtropical anticylones ~ 150E, with another pair ~105-110E. The former is linked with the SST boundary forcing while the latter may be linked to the Indian Ocean convection, all discussed above. However, for about the past week, the anticyclonic circulation gyre ~35N/105E (the northern member of the twin pair) has had 250mb wind speed anomalies ~30-40m/s. While attribution to this feature cannot be done here, it is possible the East Asian topography has played a role, going back to the mountain torque component. This anticyclone is interacting with baroclinic wave packets which will contribute the expected western North American ridge by this upcoming weekend.

Uncertainty continues extremely high. It is plausible to expect GSDM Stage 2 week 1, meaning western North American ridge and central/eastern USA trough by this coming weekend into early next week. Most numerical ensemble prediction systems agree with this. I also like the notion of continued retrogression of the western USA trough to ~140W by week 2, as many numerical models are showing. This would be a maturing of the Stage 2 response. However, should the convection across the Tropical Northwest Pacific become very intense during week 2 (per above), the synoptic pattern across North America “could be almost anything”. I am also concerned that more westerly flow may once again be added to the atmosphere later week 2 into week 3, meaning a possible return to GSDM Stage 3. Recall there is still slightly above average zonal mean and global westerly flow throughout the atmosphere. How much additional reduction there will be before going back up is unclear.

Week 1 (20-26 July 2006): GSDM Stage 2 is most probable. While intense heat returns to the western USA by this weekend, cooler and wetter weather can be expected for the central and eastern states. Severe local storms and heavy rainfall should spread from the Mississippi Valley into the eastern states with the developing trough. Toward the end of this period the ridge may shift back into the eastern Pacific while generally cyclonic flow dominates much of Canada and the northern USA. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.

Week 2 (27 July - 2 August 2006): A mature GSDM Stage 2 would be probable at the start of this period, possibly followed by Stage 3 at the end. Synoptically there may be a deep trough from Hudson’s Bay into the Northern Rockies and Northern Plains with a southeast states ridge. Above average westerly flow along the USA/Canada border may return afterwards. Temperatures would again warm to above average values for much of the southcentral into the eastern part of the country while at least more seasonal readings occur across the northern states. An active MCS track may become quite robust from the Northern Rockies/Plains to Great Lakes this period.

Week 3 (3-9 August 2006): Unclear. However, an option to monitor will be a return to a situation similar to the current one should a summertime rendition of GSDM Stage 3 become quite robust.

A welcome cool down (likely brief) seems like a good bet for Southwest Kansas by this weekend, with maximums perhaps in the 80s on roughly Saturday. At least one or two rounds of scattered thunderstorms are probable ~Thursday night into this weekend. Afterwards temperatures will warm, possibly back to ~100F by the middle of next week. Above average temperatures with a few opportunities of scattered storms appear probable going into August.

The time -filtered coherent modes Hovmoller plots of OLR and OLRA are at http://www.cdc.noaa.gov/map/clim/olr_modes/), velocity potential Hovmollers at http://www.cpc.ncep.noaa.gov/products/intraseasonal/vpot_tlon.html , and an animation of velocity potential overlayed on OLRAs are at http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ir_anim_monthly.shtml.

Satellite imagery and other information can be found from the following links: eastern hemisphere, full-disk west Pacific, mtsat, IO, Africa, http://www.jma.go.jp/en/gms/ ; other imagery here. Latest tropical cyclone statements can be found from http://www.nhc.noaa.gov/, while the latest 3-day averages of OLR totals and anomalies and other data can be found here

http://www.cdc.noaa.gov/map/clim/glbcir.anim.shtml (animations of various fields from the operational data)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml (Global Tropical Hazards Assessment available from this site, along with other useful information)

http://www.cdc.noaa.gov/map/clim/aam.rean.shtml (reanalysis AAM plots)

http://www.cdc.noaa.gov/map/clim/aam.shtml (operational AAM plots)

Latest CDC Ensemble Forecast

Latest NCEP Ensemble Forecast

Additional NCEP Ensemble Output

Latest Canadian Ensemble Output

Latest Deterministic ECMWF Forecasts

http://www.cdc.noaa.gov/people/jeffrey.s.whitaker/refcst/week2/

http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html (link to our Weather-
Climate discussions)

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html (model performance; please navigate to others)

Please see the CPC Drought Monitor for areas of dryness and the latest official outlooks and statements from the Storm Prediction Center not only for severe storms, but also fire weather concerns. Finally, the CPC USA Hazards Assessment for offers additional insights not only for possible week 1 high impact weather, but week 2 as well.

I will try to do another posting this upcoming weekend. Work is also on-going to post a weather-climate discussion on the ESRL/PSD MJO web site hopefully by early August.
Ed Berry

Saturday, July 15, 2006

Global Westerly Flow Update

Wednesday, July 12, 2006

Above Average Global Westerly Flow is about to Collapse

The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).

http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf

From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.

Global tropical SSTs continued a general cooling trend during the past week, especially across portions of the Indian Ocean, extreme west Pacific and Atlantic Oceans. SSTs in these regions lowered by as much as 1C, and were largely a feedback from increased clouds and rainfall. Still, near to above average SSTs remained from the South Pacific into the Tropical Northwest Pacific, as well as along the East Pacific equatorial cold tongue. In fact, anomalies ~ plus 1-2C extended to roughly 200m deep just to the east of the equatorial date line, and that may be the start of another oceanic Kelvin wave per latest TAO data. Actual SSTs in excess of 29C still dominate from the South Pacific into the Indian Ocean, and nearly all of the Tropical Northwest Pacific. Additional global SST information can be obtained from latest TAO data here, ESRL/PSD data here, CPC data

http://www.cpc.ncep.noaa.gov/products/predictions/threats/index_gloss.html,

and BMRC at

http://www.bom.gov.au/bmrc/ocean/results/climocan.htm .

The following are links to ENSO discussions (recently updated).

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html

Tropical convective forcing has strongly re-emerged (and flared-up) into the central and eastern equatorial Indian Ocean toward the Bay of Bengal and Southeast Asia during the past week. Anomalies of outgoing longwave radiation (OLRA) have been ~minus 30-50 W/m**2. The time filtered coherent modes Hovmollers present very weak evidence of convectively coupled Kelvin waves coming back around from the Western Hemisphere initiating this tropical rainfall. However, daily monitoring also suggests jet streak dynamics linked to austral winter Southern Hemisphere baroclinic wave activity may have also contributed, particularly since the convection did start south of the equator. Whatever the case may be, we continue to observe the ~30 day variability of tropical convective forcing across the Indian Ocean. Additionally, time-latitude sections of OLR/A show at least 2 episodes of northward propagation from the equatorial Indian Ocean into southern Asia since early May, reflecting the seasonal cycle. I think we are seeing another such episode, working along with the currently well established and very intense active Indian and Southeast Asia Monsoon systems.

Farther to the east tropical convection across the west central and northwest Pacific remains strong while shifting northwest. At least 3 tropical cyclones have developed in this region (see http://www.npmoc.navy.mil/jtwc.html for details) during the past week. As discussed last week, this region of enhanced tropical thunderstorm activity has been part of a ~4-6 week persistent area of SST boundary forcing extending from the South Pacific then toward Southeast Asia. Latest Hovmoller and other plots suggest suppression is returning to the equatorial west Pacific (as enhancement shifts northwest), while ~minus 5 W/m**2 OLRA persists south of the equator. Latest full disk satellite imagery shows a weaker region of thunderstorm activity from ~140E-180 within 10 deg. of the equator. Hence there are currently two areas of tropical forcing (once again) across the eastern hemisphere, with the western area easily the most intense.

A weak eastward propagating convectively coupled dynamical signal is also present across the Western Hemisphere tropics, part of the fast eastward propagating modes observed since April. Per Hovmoller plots of velocity potential anomalies and additional animations of combined fields, this signal was centered ~90-120W as of July 10th, moving east at about 12 m/s (there has been a loose wave 1 signature of the global velocity potential field at times). The coherent modes do not project this signal onto a convectively coupled Kelvin wave. At least 2 tropical cyclones have recently developed across the East Pacific perhaps as a result of strengthened cross equatorial low level flow (please see TPC link below for details).

TAO buoy data through July 11th show that surface wind anomalies have become very weak within 5 deg. of the equator east of 140E to near the South American coast. The equatorial westerly wind anomalies observed near the date line a week ago have propagated into both hemispheres linking up with the northwest Pacific tropical cyclones and Southern Hemisphere frontal activity. However, Hovmoller plots of daily mean (through July 11th) near equatorial surface wind show that while weak easterly anomalies have returned from just west of the date line to Indonesia, westerly anomalies ~5-7 m/s were present from ~60-90E (consistent with the tropical forcing). Monitoring will be needed to see if this next round of surface westerlies comes out to the date line along the equator.

As stated last week, it is somewhat unusual to see surface westerly flow on the equator this time of year (usually north). However, we observed this kind of behavior during summer 2004 (see weather-climate discussions), prior to the 2004-05 warm event. Per above, the TAO buoy data already suggest weak evidence that a downwelling oceanic Kelvin wave was initiated by the westerly wind event (WWE) last week. Another WWE may intensify that process, possibly leading to a warming of the equatorial eastern Pacific.

Empirical, statistical and numerical prediction tools continue to be inconclusive for useful information about the future evolution of the tropical convection. Please see ESRL/PSD MJO tools , BMRC MJO tools, CPC MJO tools, and http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html for the details (and draw your own conclusions). These tools generally rely on a moderate to strong MJO signal, which is nearly non-existent at this time. West Pacific SST boundary forced, fast dynamical signals and intense eastern hemisphere monsoon systems dominate the tropical convective forcing.

Zonally averaged anomalies of upper tropospheric zonal wind continue to propagate poleward and downward (see July 5th posting). Time-latitude sections of 200mb zonal mean zonal wind anomalies still indicate most of the tropical and subtropical atmospheres to be dominated by westerlies. Largest magnitudes were ~ 10S and 30N, with values of nearly 10 and 5 m/s, respectively. However, especially from 5-10N, values were returning to near normal.

A much more complete understanding of the poleward propagation of circulation anomalies and forcing-response-feedback relationships requires a vertical average of zonal mean anomalies and a global summation (regional considerations and other dynamical processes understood). This is one reason to make use of the atmospheric angular momentum (AAM) plots from ESRL/PSD (links below). While tropospheric global relative AAM is still ~1.5 standard deviations (sigma) above the 1968-1997 reanalysis climatology (1 sigma above the operational 1979-1998 operational data climatology), the tendency is becoming negative (as of July 9th for the reanalysis data). Much of the tendency is coming from the mountain and frictional torques, globally ~ minus 10 and 15 Hadleys, respectively. Of course, the Southern Hemisphere is contributing “a lot” to these signals this time of year.

Weather-climate linkage signals have been incredibly mixed and confusing for the past several weeks. However, the above discussed AAM behaviors are consistent with tropical convective forcing re-emerging into the Indian Ocean along with other subseasonal modes of variability making up the GSDM as discussed in our paper. One of these may have included a “mountain-frictional torque index cycle”. Anomalous westerly flow is reaching the Earth’s surface of the subtropical (trades are weakening across the Tropical North Atlantic, for example) and extratropical atmospheres while negative mean sea level pressure anomalies (MSLPA) are starting to be observed along the east slopes of major north-south mountain barriers globally. Negative MSLP anomalies are also appearing across the Arctic (links to various animations are given below). The point is that the Earth’s surface is removing angular momentum (westerly flow) from the atmosphere, allowing the Earth to gain it (meaning a faster rotation rate and a shortening of the length of day by a few milliseconds!). Hence a collapse of the anomalous atmospheric westerly flow (including the anomalously strong North Pacific jet for this time of year) is expected during the next few weeks.

Animations of daily mean anomalies of 150mb and 250mb vector winds show distorted twin subtropical anticylones ~140-150E (the northwest Pacific tropical cyclones are contributing), with a signal of redevelopment across the Indian Ocean. The latter is tied to the tropical convective flare-up discussed above (easterly anomalies starting to appear at 150mb). There is a fast Rossby wave energy dispersion interacting with the twin subtropical anticyclones leading to yet another anomalous anticyclonic gyre across the north central Pacific. These result is a strong North Pacific Jet with 250mb wind anomalies ~30-40m/s around 50N, and a subtropical jet (STJ) with 150mb anomalies ~plus 15-20 m/s extending into the Desert Southwest (suppressing the monsoon system there). As most global models show, this strong North Pacific Jet will move across the northern part of the USA over the next several days.

Within the GSDM framework, still largely from the zonal mean wind signal from the subtropical atmosphere and the AAM budget (including a possible mountain-frictional torque index cycle), I think there is now a reasonable argument for a boreal summertime rendition of a Stage 3 circulation, about to transition to Stage 4. The strong westerly flow across the North Pacific is supportive of this notion, where strong interactions with the extratropics have contributed.

Uncertainty remains very high for the outlooks that follow, but maybe a bit less than recently given the above. Reasonably good model agreement also minimizes some of that concern for week 1. However, only broad and hopefully statistically useful statements can be offered.

My own thoughts would be to see the renewed Indian Ocean convection move out into the west central and northwest Pacific by late week 2 or 3, behaving similar to the previous 2 events discussed above. This would enhance the SST boundary forced tropical convection in that region, and may contribute to a retrogression of extratropical circulation anomalies across the Pacific-North American (PNA) sector. The role the fast dynamical signal contributes is unclear. There has been a slight tendency for that signal to become less coherent while the convection across the Eastern Hemisphere intensifies. A change to GSDM Stage 4 may occur during week 1, followed possibly by Stage 1 sometime weeks 2-3. One big concern I have is Stage 1 getting bypassed and going to GSDM Stage 2 “quickly”. Interestingly this possibility was mentioned in my last posting dated July 5th. Let’s just see what happens.

It is possible that a transition from the previous cold event (La-Nina) to perhaps an oncoming warm event (El-Nino) may be occurring. Stay tuned for additional information on the latter per links given, especially from CPC.

Week 1 (13-19 July 2006): Strong westerly flow across the northern USA with a broad central states ridge looks like a good bet. Whether or not there are multiple centers to this ridge are unclear synoptic details. I am also unclear just how long the STJ across the Desert Southwest will persist (suppressing their local monsoon system). GSDM Stage 4 would suggest twin subtropical anticyclones across the Western Hemisphere. Perhaps these may set up around 60-90W given the dynamical signal per above, maintaining the STJ across the southwest USA.

The well advertised heat wave (at least loosely) should be on track for most of the country, with the largest positive temperature anomalies centered from the Northern Rockies into the Upper Mississippi Valley. Some locations in these areas will exceed 100F, with high points well into the 70s for locations such as Iowa. There may be some pockets of intense/severe thunderstorms across the northern part of the country linked to jet streaks and frontal activity. Most/all drought stricken parts of the country will not get much relief. With the trades relaxing across the Tropical North Atlantic and the possibility of reduced shear due to twin subtropical highs, there may be a concern for tropical cyclones particularly across the Caribbean later this period going into week 2. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information. Other types of summertime weather/hazards around the country in this situation should be apparent.

Week 2 (20–26 July 2006): An option that must be monitored is retrogression with amplification across the PNA sector. This may result in a ridge from western North America into Alaska, a central USA/Great Lakes states trough (~90W?) and a ridge across the southeastern part of the country/western Atlantic Ocean (one summertime version of GSDM Stage 2). Much cooler weather for the North Central States with above average rainfall for roughly the eastern half of the country would be expected if this occurred (similar to late June).

Week 3 (27 July – 2 August 2006): Same as week 2, otherwise unclear.

Hot daytime temperatures with maximums from the mid 90s to around 105F and little organized rainfall are likely for Southwest Kansas through much of week 1. I cannot rule out a heavy rainfall surprise somewhere in this part of the world. If there is any truth to the possibility of GSDM Stage 2, much cooler temperatures and an improved opportunity for rainfall would exist sometime during weeks 2-3.

The time -filtered coherent modes Hovmoller plots of OLR and OLRA are at
http://www.cdc.noaa.gov/map/clim/olr_modes/), velocity potential Hovmollers at http://www.cpc.ncep.noaa.gov/products/intraseasonal/vpot_tlon.html , and an animation of velocity potential overlayed on OLRAs are at http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ir_anim_monthly.shtml.

Satellite imagery and other information can be found from the following links: eastern hemisphere, full-disk west Pacific, mtsat, IO, Africa, http://www.jma.go.jp/en/gms/ ; other imagery here. Latest tropical cyclone statements can be found from http://www.nhc.noaa.gov/, while the latest 3-day averages of OLR totals and anomalies and other data can be found here
http://www.cdc.noaa.gov/map/clim/glbcir.anim.shtml (animations of various fields from the operational data)
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml (Global Tropical

Hazards Assessment available from this site, along with other useful information)

http://www.cdc.noaa.gov/map/clim/aam.rean.shtml (reanalysis AAM plots)

http://www.cdc.noaa.gov/map/clim/aam.shtml (operational AAM plots)

Latest CDC Ensemble Forecast

Latest NCEP Ensemble Forecast

Additional NCEP Ensemble Output

Latest Canadian Ensemble Output

Latest Deterministic ECMWF Forecasts

http://www.cdc.noaa.gov/people/jeffrey.s.whitaker/refcst/week2/

http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html (link to our Weather-
Climate discussions)

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html (model performance; please navigate to others)

Please see the CPC Drought Monitor for areas of dryness and the latest official outlooks and statements from the Storm Prediction Center not only for severe storms, but also fire weather concerns. Finally, the CPC USA Hazards Assessment for offers additional insights not only for possible week 1 high impact weather, but week 2 as well.

I will try to do another posting this upcoming weekend.
Ed Berry

Wednesday, July 05, 2006

Like it or not, Uncertainty Rules

The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).

http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf

From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.

There has been some cooling of the global tropical SSTs during the past week, particularly across the Indian and North Tropical Atlantic Ocean basins. SSTs across the latter regions have lowered as much as 1.0 deg C. However, anomalies remain above normal west of 170W with ~plus 1-2 deg C warmth down to roughly 200m. Actual SSTs in excess of 29C dominate from the South Pacific into the Indian Ocean, and nearly all of the Tropical Northwest Pacific. Additional global SST information can be obtained from latest TAO data here, ESRL/PSD data here, CPC data

http://www.cpc.ncep.noaa.gov/products/predictions/threats/index_gloss.html,

and BMRC at

http://www.bom.gov.au/bmrc/ocean/results/climocan.htm .

The following are links to ENSO discussions.

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html

There is some evidence that a slower mode of tropical convective forcing may be emerging. Per coherent modes Hovmollers of OLR/OLRA and other plots, boundary forcing from the warm SSTs west of the date line has led to roughly a 4-5 week persistence of enhanced convection along and south of the equator. The most active region has been centered ~160E with OLR anomalies ~ minus 30-50 W/m**2. Several convectively coupled Kelvin waves (fast dynamical signals) have propagated eastward through this SST boundary forced convection. For instance, about 2-3 weeks ago (~June 17-18) one of these Kelvin waves returning back into the Eastern Hemisphere lead to an intense convective flare-up across warm equatorial Indian Ocean SSTs. A fast Rossby wave energy dispersion from this flare-up propagated into the northern extratropics, interacting with the slower SST boundary forced Tropical West Pacific convection as it did. The response was a downstream retrogression and amplification of the western North American Ridge, a deep central USA trough and an anomalous anticyclone just east of New England. It was this chain of events that resulted in the tremendous rainfall which affected much of the USA East Coast.

The latest in the “series” of these convectively coupled Kelvin waves (at least 2 of them) has moved into the Western Hemisphere. A response has been for somewhat enhanced rainfall from the east Pacific ITCZ into lower Central America with suppression of the recently active Indian and Southeast Asian monsoon systems. While intense convection still persists across the west central and northwest Pacific (including Typhoon Ewiniar see http://www.npmoc.navy.mil/jtwc.html ), there is also suppression across the Indian Ocean. Linear thinking would suggest the enhanced convection portion of the fast dynamical signal to once again return to the Eastern Hemisphere by roughly the end of week 2. We will see.

All of the above discussed tropical convective variability/forcing have led to another equatorial westerly wind event from 150E to the date line. TAO buoy data through July 4th indicated westerly anomalies of at least ~5-10 m/s, and is the third such event since about March of this year. It is somewhat unusual to see surface westerly flow on the equator this time of year (usually north). However, we observed this kind of behavior during summer 2004 (see weather-climate discussions), prior to the 2004-05 warm event. Attention needs to be paid if another down welling Oceanic Kelvin wave is initiated by these westerlies, which would lead to a warming of the equatorial eastern Pacific. In summary, while slower tropical west Pacific SST boundary forcing may be evolving, convectively coupled Kelvin waves appear to be dominating the dynamical signal.

Empirical, statistical and numerical prediction tools continue to be inconclusive for useful information about the future evolution of the tropical convection. Please see ESRL/PSD MJO tools , BMRC MJO tools, CPC MJO tools, and http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html for the details (and draw your own conclusions).

During the past 4 weeks or so we have seen nice signals of poleward propagating zonal mean zonal wind anomalies. During the first half of June there were zonal mean anomalous easterlies propagating off the equator into the subtropical and lower midlatitude atmospheres, followed by westerlies. In fact, 200mb zonal mean easterly anomalies have propagated to at least 45N, helping to support strong ridges across the northern extratropics. Vertically averaged zonal mean westerly wind anomalies dominate the tropical and subtropical atmospheres, with magnitudes of ~10 m/s around 20N at 200mb (not 10-20 m/s as incorrectly stated on my July 1st posting). A separate maximum of about 5 m/s has appeared during the last few days just south of equator, and is likely linked to the west Pacific SST boundary forced convection.

It must be remembered that these zonal mean zonal wind anomalies do not just propagate poleward, but downward as well (see our paper for references). The global frictional torque, after being positive for about a couple of weeks, has now dropped to ~minus 10 Hadleys based on the reanalysis data through July 2nd. This is telling us that some of the upper tropospheric westerly flow is now reaching the Earth’s surface, which will help bring down the strong positive global mountain torque (roughly a 6 day lag, on average). The AAM tendency is still positive at roughly 10-15 Hadleys, but well off its positive maximum. Based on the 1968-1997 reanalysis climatology, tropospheric relative AAM is ~ ½ of a standard deviation above normal (see links below for AAM plots).

Animations of daily mean 150mb and 250mb vector wind anomalies (need to look at the totals also) present a very complex circulation (understatement!). There is some evidence that the Atlantic equatorial westerly wind anomalies have worked back into the Indian Ocean, especially at 250mb (consistent with suppression). Meanwhile subtropical westerlies continue across the North Pacific with 250mb anomalies still ~20 m/s. Rossby wave energy dispersion across north Asia is interacting with the divergent outflow from the west Pacific tropical convection, maintaining an anomalous cyclone across the North Pacific. The latter is combining with the above average subtropical Pacific westerlies, leading to strong westerly flow approaching the USA. Across North America a moderate amplitude ridge exists across the Rockies with a trough to the east.

Within the GSDM framework, largely from the zonal mean wind signal from the subtropical atmosphere and the AAM budget (including a possible mountain-frictional torque index cycle), I think there is some argument for a boreal summertime rendition of a Stage 3 circulation. The relatively strong westerly flow across the North Pacific (loosely speaking) and cyclonic flow particularly south of Alaska to the Pacific Northwest (and downstream ridge-trough pattern) also support that notion. This possibility has been suggested in the last couple of postings.

Uncertainty reigns supreme where the atmosphere goes from here, especially after week 1. There are forecasts of opportunity, including prediction of extreme weather events, which do occasionally arise for weeks 2-4 (especially week 2). However, uncertainty dominates, and in our current situation, I think even more than “usual” (boreal summer and other issues understood). It is possible that a transition from previous cold event (La-Nina) to perhaps an oncoming warm event (El-Nino) may be part of the issue. Stay tuned for additional information on the latter per links given, especially from CPC.

Week 1 (6-12 July 2006): More westerly flow is coming into the western USA (per above), leading to a deamplification and downstream progression of the current western CONUS ridge (split flow displaced northwest). Most models are showing this solution. Moisture transport from the deep tropics of the east Pacific is occurring into the Desert Southwest while there is improvement from the Gulf of Mexico. An active storm track with the strong westerlies (for this time of year) may become established from the Pacific Northwest to New England, while a weaker southern branch crosses the southern Rockies into the central Plains. In this type of synoptic pattern, moisture transport from the Gulf of Mexico should be robust due to lee-side Rocky Mountain troughs.

Active and possibly severe MCSs/Derechoes (along with areas of heavy rainfall) from the Northern and Central Plains into the Great Lakes and Ohio Valley will continue to be a concern. The moisture transport into the southwest states may become suppressed while possibly excessive heat/humidity builds across the Plains and heads east. The Tropical North Atlantic looks to remain unfavorable for tropical cyclogenesis due to upper tropospheric anomalous westerly flow. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information. Other types of summertime weather/hazards around the country in this situation should be apparent.

Week 2 (13–19 July 2006): While tropical convection may remain enhanced across the western and northwestern Pacific (while maybe shifting slightly to the west), at least a weak dynamical signal could emerge across the Indian Ocean, all by the end of this period. A synoptic pattern similar to week 1 may start this period. Afterwards, no statistically useful information can be offered.

Week 3 (20-26 July 2006): Same as week 2. One option to monitor will be for the North American ridge position to shift back toward the west coast into Alaska, leading to a downstream trough across the central USA and a southeast states ridge.

A decent opportunity of rainfall exists for Southwest Kansas this upcoming weekend, followed by a return to summertime heat next week. With good Gulf of Mexico moisture transport, at least diurnal thunderstorm activity focusing along the lee-side trough then moving east would be expected. Forecast is unclear, afterwards. However, I think rainfall opportunities will continue the rest of this summer (as opposed to totally dry, per earlier fears).

The time -filtered coherent modes Hovmoller plots of OLR and OLRA are at http://www.cdc.noaa.gov/map/clim/olr_modes/), velocity potential Hovmollers at http://www.cpc.ncep.noaa.gov/products/intraseasonal/vpot_tlon.html , and an animation of velocity potential overlayed on OLRAs are at

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ir_anim_monthly.shtml.

Satellite imagery and other information can be found from the following links: eastern hemisphere, full-disk west Pacific, mtsat, IO, Africa, http://www.jma.go.jp/en/gms/ ; other imagery here. Latest tropical cyclone statements can be found from http://www.nhc.noaa.gov/, while the latest 3-day averages of OLR totals and anomalies and other data can be found here
http://www.cdc.noaa.gov/map/clim/glbcir.anim.shtml (animations of various fields from the operational data)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml (Global Tropical
Hazards Assessment available from this site, along with other useful information)

http://www.cdc.noaa.gov/map/clim/aam.rean.shtml (reanalysis AAM plots)

http://www.cdc.noaa.gov/map/clim/aam.shtml (operational AAM plots)

Latest CDC Ensemble Forecast

Latest NCEP Ensemble Forecast

Additional NCEP Ensemble Output

Latest Canadian Ensemble Output

Latest Deterministic ECMWF Forecasts

http://www.cdc.noaa.gov/people/jeffrey.s.whitaker/refcst/week2/

http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html (link to our Weather-
Climate discussions)

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html (model performance; please navigate to others)

Please see the CPC Drought Monitor for areas of dryness and the latest official outlooks and statements from the Storm Prediction Center not only for severe storms, but also fire weather concerns. Finally, the CPC USA Hazards Assessment for offers additional insights not only for possible week 1 high impact weather, but week 2 as well.

I am going to be on travel this upcoming weekend. Hopefully I will be able to post an update on about the middle of next week.
Ed Berry