Postponed; A break from El-Viejo???

Shift work and other issues preclude a complete discussion until hopefully next weekend. In summary, the friction-mountain torque index cycle variation addressed on the 19 April posting is evolving. A response has been the expected “downward turn” in the WB (2007, 08) GWO phase space, in phase 4 updated through 22 April.

Magnitudes of daily mean vector wind anomalies at 250mb on 24 April were in excess of 30m/s over northeast Asia which is directly attributable to the ~25 Hadley East Asian mountain torque updated through 22 April. This jet streak, as part of fast Rossby wave energy dispersion (RWD) processes interacting with the intensifying Eastern Hemisphere tropical convective forcing (more said below), is likely to dig a trough into the western USA next week. More and more numerical models have been trending toward the above with varying solutions. From a weather prediction point of view, I would favor the slower and farther south solutions such as the deterministic ECMWF model valid mid-late next week.

The tropical convective forcing has been steadily getting better organized across the Eastern Hemisphere during the last week. Full disk satellite imagery and other tools suggest the centroid of this intense-severe tropical rainfall at ~120E just north of the equator while extending from the eastern Indian Ocean east-southeast into the South Pacific Ocean Convergence Zone (SPCZ). Having ENSO removed, WH (2004) phase space plots show little projection onto a MJO. Leaving the interannual variability in, there is a greater than 1 standard deviation MJO projection in WH (2004) phase space, phase 4. Coherent modes Hovmollers suggest a weak MJO projection, along with some eastward propagation during the last couple of weeks. Regardless of whether or not we have a “true” MJO, as often observed this past boreal cold season, tropical-extratropical coupling is again occurring leading to approximately the same phases of both the GWO and MJO (latter leaving ENSO in). The dynamics explained by the GWO (including AAM transports in addition to the surface torques) give some reasoning to these types of interactions. Again, the GWO is a dynamical measure of the global and zonal mean circulation.

I think it is probable for the Eastern Hemisphere tropical convective forcing to shift into the west central and southwest Pacific Ocean during the next few weeks. While the details of GWO evolution are always unclear (red noise processes are part of it), I also think it is probable to see a circuit into phase 5, before once again collapsing. Animations of upper and lower tropospheric daily mean vector wind anomalies not only present a strong signal of the expected tropical baroclinic response to the convective forcing, but also interactions with RWDs outside the tropics, all supportive of the above. Additionally, various diagnostics show strong zonal mean easterly wind flow anomalies propagating poleward well into the subtropical and midlatitude atmospheres, ~25-30N and ~40S. Tied to the above, zonal mean westerly wind flow anomalies have been increasing in the equatorial upper troposphere during particularly the last week-10 days. Much of that is from the Western Hemisphere Pacific Ocean linked to the twin cyclones near the date line. An important monitoring issue is if these anomalous westerlies also propagate poleward and downward during the next few weeks.

Once the tropical convective forcing comes out into the west Pacific, meridionally oriented RWDs are likely, perhaps shifting a trough farther east into the Plains. Given higher latitude blocking forced by zonal mean AAM transport considerations, a cold and wet pattern for much of the lower 48 states focusing on the central states is a forecast option by ~weeks 2-3.

In the longer term, La-Nina SSTs continue to moderate. However, the global and zonal mean circulation base state still has a good memory of this past “season of the witch”. Stay tuned.

Links below are to additional SST information.

http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html

http://www.pmel.noaa.gov/tao/jsdisplay/

http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18).

There is no change to the USA and global outlooks discussed on 19 April. As mentioned above, the greatest negative anomalies for below normal temperatures may focus on the central states ~weeks 2-3. Beyond that, retrogression of existing circulation anomalies not only due to subseasonal activity but also climatology may occur shifting an active storm track northwest. I continue to leave it to the expertise of the appropriate weather centers internationally to alert the public of additional weather hazards worldwide.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing time series of normalized global relative AAM time tendency (Y-axis) and normalized global relative AAM anomaly (X-axis) can be found at

http://www.cdc.noaa.gov/map/clim/gsdm.shtml

WB are in the process of redoing the GWO phase space plot to make it appear more realistic, physically. We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous to the WH (2004) “convention”. In addition, the GWO plot does not have the ENSO signal removed.

Please see the revised description of the GSDM per above link. Also, I encourage the readers to study the annotated MJO and GWO phase space plots to help relate the global variations explained by those techniques to “weather”.

Links to CPC and PSD ENSO discussions:

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

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

The following is a link to information about the stratosphere:

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, a two-part paper is in active preparation by WB that will formally introduce the GWO along with subseasonal composites. Given shift work and upcoming travel, updates will always remain extremely difficult. I will try to post another discussion next weekend, 3-4 May.

Ed Berry

Circumglobal Teleconnection

The spatial distribution of global SSTs still includes weakening but persistent below normal waters along the equatorial Pacific Ocean from ~160E-120W. Magnitudes are as low as roughly minus 1.5C extending to 150m deep per latest 5-day averaged TAO buoy data. Shallow but very warm anomalies continue across the far eastern Pacific Ocean to South America, while significant positive anomalies in excess of 5C are present around 200m deep/160E along the equator.

Needless to say careful detailed rigorous daily monitoring is a must as part of any forecast process to gain some understanding on the future of El-Viejo. There are a couple of outlier statistical and dynamical models suggesting El-Nino SSTs by boreal winter 2008-09. Whatever the case, confidence in any objective predictive scheme must be very low right now, and remember that SSTs from other basins including the tropical Indian and Atlantic Oceans are also important. As discussed below, the current global circulation base state is strongly La-Nina. Links below are to additional SST information.

http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html

http://www.pmel.noaa.gov/tao/jsdisplay/

http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18).

In the spirit of brevity, full disk satellite imagery and other diagnostic monitoring tools indicate that the tropical convective forcing across the central and eastern equatorial Indian Ocean has been strongly organizing during the last several days. The greatest concentration is ~0/80E having 3-day averaged OLRA in excess of minus 70 W/m**2. Sporadic convection continues across other portions of the tropics that we should all be familiar with. SSTs have cooled too roughly minus 1-2C in the region of where the severe Indian Ocean thunderstorm activity is, with warming across the equatorial west central Pacific Ocean. My point is I suspect, with forcing from the dynamics captured by the GWO, MJO #5 for this boreal cold season (time of year, and all other arguments understood) may be evolving. WH (2004) phase space plots for the MJO through 18 April have a near zero projection. There is already a westerly wind burst (WWB) across the equatorial Indian Ocean and a WWB across the west central Pacific Ocean is a possibility during the next few weeks.

Global relative AAM, updated through 17 April per ESRL/PSD, is roughly 2.5 sigma below the R1 data climatology. Not only is the global circulation in our familiar low AAM base state, there is evidence of (again) merdional symmetry of zonally symmetric zonal mean wind flow anomalies (vertically and zonally integrated for the latter). That is, weak equatorial zonal mean anomalous westerlies flanked by zonal mean easterly wind flow anomalies across the subtropical atmospheres. The greatest subtropical zonal mean easterly wind flow anomalies persist across the Northern Hemisphere, having magnitudes ~10-15m/s at 200mb. Westerly wind flow anomalies are present across the mid and higher latitudes; again, particularly the North Hemisphere. That is why anomalous ridges are present across the midlatitudes (as seen in the earth component of the angular momentum budget) leading to anomalous poleward shifted storm tracks, in the zonal mean.

Various animations of several wind fields show that the zonal mean equatorial westerly wind flow anomalies are largely coming from the upper troposphere of the Western Hemisphere Pacific Ocean. The latter is part of the expected baroclinic response to the Eastern Hemisphere tropical convective forcing. Anomalous twin upper tropospheric tropical/subtropical anticyclones are developing in the region of the Indian Ocean/Indonesian divergent outflow.

The WB (2007, 08) GWO, which is a much better quantitative measure of the global circulation than an equatorially confined empirical MJO index in our current situation, has orbited to a roughly 2 sigma phase 4 projection. The global tendency of relative AAM is ~plus 25 Hadleys which not only has had a contribution from the tropical forcing, but also a recent spike in the global frictional torque of ~plus 20 Hadleys. This strong positive frictional torque has been forced by anomalous surface easterlies from the strong midlatitude ridges discussed above. The point to all this is we have another example of tropical-extratropical coupling, observed so often this past cold season. The WB (2007, 08) GWO can tell us a lot about the dynamics of the non-linear complicated forcing-response-feedback relationships involved.

The punch line to this posting is because of all the scientific issues discussed above (and those I left out), zonally oriented Rossby wave energy dispersions (RWDs) continue to be favored in our current base state (due to trapping of baroclinic energy in the jets). This has been the case since at least November 2007, with a few exceptions such as ~1 December 2007 and earlier this month. As discussed in my last posting, most numerical model predictions failed badly on the latter (see link below as an example).

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html .

The zonally oriented chains of circulation anomalies responding to the RWDs not only favor a central Pacific Ocean ridge, but can also impact the weather globally. Focusing on just the Northern Hemisphere, what I am referring to is not a regional scale teleconnection pattern like the PNA, but a pattern connecting widely separated points all across globe. This pattern has been documented by Branstator (2002), and he has termed it as a “circumglobal teleconnection”. We have observed this type of pattern frequently for years, and this is contained in the legacy WB (2007) Stages 2 and 4 of the GSDM. More recently, WB (2007, 08) have captured this circumglobal teleconnection pattern in composites done on phases 3 (La-Nina like) and 7 (El-Nino like) of the GWO. A two-part paper is in preparation.

The circumglobal teleconnection pattern is currently present, and has been for roughly the last week. Where the atmosphere goes during the next few weeks will depend a lot on whether or not the Eastern Hemisphere tropical forcing comes out into the west central Pacific Ocean. While uncertainty is huge, my feeling is an eastward shift is probable and my outlooks for the USA below reflect that. That eastward shift of tropical convective forcing may also be in sync (at times) with the phases of the GWO, which is also probable to circuit into phase 5 before collapsing. Please recall my discussion from last week about the USA being impacted by the tropical forcing regardless of whether or not we have a “WH (2004) MJO”.

A relatively repeatable pattern of troughs coming into the western USA then the Plains is likely to continue. While timing is white noise, I am thinking the tropical convective forcing will come out into the west central Pacific Ocean ~weeks 2-3. If that is the case, baroclinic energy may become dispersive allowing for great circle RWD routes like that seen earlier this month. An eastward shift of wave trains across the USA would then be expected (with retrogression afterward), as well as a strengthening subtropical jet. In any case, the broken record USA outlooks continue. The storm track will be very active but anomalously northward shifted. Meridional amplification would allow the storm track to temporarily shift south against the seasonal cycle. Weather ramifications are “obvious”.

I do want to make “special mention” of anomalous cold Arctic air that has been building up in western Canada for the last several days. That is a response to blocking developing in the region of Alaska (one of the matters I did not discuss). Initial impacts from this airmass are already being felt across the extreme northern Rockies. Depending on the timing of subseasonal events discussed above, in addition to what may be a vicious severe local storms outbreak for portions of the Plains and the Ohio Valley, a late season significant winter storm (with intense thundersnow) is possible for locations such as the Upper Mississippi Valley and Northern Plains. Having my reasons tied to somewhat faster time scales explained by the GWO (friction-mountain torque index cycle), this extreme weather situation may occur ~week 2. Those faster time scales may also bring the tropical convection into the west Pacific sooner. Stay tuned.

My concerns of prolonged dryness remain for the central and southern High Plains. The faster time scales scenario discussed above would be more favorable for precipitation in these areas, as would any eastward shift of tropical forcing into the west central Pacific Ocean.

Locations from the Indian Ocean into at least western Indonesia are likely to get hammered with intense to severe thunderstorm activity week-1, shifting eastward weeks 2-3. The Philippines and portions of Southeast Asia are probable to be impacted particularly weeks 2-3. Tropical cyclone concerns also remain, and I suspect given the WWB (per above) the Bay of Bengal could be impacted as early as week-1. Climatologically, the Bay of Bengal has one peak period of tropical cyclones during May. The west central into the southwest Pacific Ocean remains a “wild card” until further notice, particularly given the issues discussed above. I continue to leave it to the expertise of the appropriate weather centers internationally to alert the public of additional weather hazards worldwide.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing time series of normalized global relative AAM time tendency (Y-axis) and normalized global relative AAM anomaly (X-axis) can be found at

http://www.cdc.noaa.gov/map/clim/gsdm.shtml

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous to the WH (2004) “convention”. In addition, the GWO plot does not have the ENSO signal removed.

Please see the revised description of the GSDM per above link. Also, I encourage the readers to study the annotated MJO and GWO phase space plots to help relate the global variations explained by those techniques to “weather”.

Links to CPC and PSD ENSO discussions:

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

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

The following is a link to information about the stratosphere:

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, a two-part paper is in preparation by WB that will formally introduce the GWO along with subseasonal composites. Given shift work and upcoming travel, updates remain extremely difficult. I will try to post another discussion next weekend, 26-27 April.

Ed Berry

You can't be Serious!

Given web server and time concerns, I am posting a very short update today (11 April). The spatial distribution of global tropical and extratropical SSTs along with their anomalies are generally the same today as they were 2-4 weeks ago. There are weak positive SST anomalies from the eastern Indian Ocean into Indonesia while the weakening El-Viejo SSTs are only ~minus 1C. Subsurface warmth to ~plus 5C anomalies at 160E/200m (per latest 5-day averaged TAO buoy data) continues. However, the latter has been drifting west. Given the character of the global circulation (discussed below), there is no observational evidence of a transition to El-Nino. If the on-going cold event survives boreal spring, related weather-climate ramifications may exist for at least several more months. Links below are to additional SST information.

http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html

http://www.pmel.noaa.gov/tao/jsdisplay/

http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18).

Since the eastward propagation of tropical convective forcing into the west central Pacific Ocean and evolution to a zonal wave number 2 pattern of tropical circulation anomalies, signals involving this type of variability have been weak. Before continuing, I want to emphasize the importance that the west Pacific Ocean tropical convective forcing (located ~0/140-160E approximately 5-10 days ago) had on the USA weather this past week.

First, the tropical forcing did have a MJO component (#4 for this cold season). Nevertheless, understand that the MJO only explains ~20 percent of the tropical convective variability, on average. Whether or not the west Pacific Ocean signal was a MJO is irrelevant. The point is that meridionally directed Rossby wave energy was dispersed (RWDs) by the west Pacific convection that arced across the PNA sector and then dynamically forced the western USA trough complex. There have been at least 3 synoptic weather events with this trough, all contributing to extreme USA weather since last weekend. The latter does not occur every week in April, hence that is greater than climatology.

Secondly, and this possibility was discussed on my 15 March posting (and followed up last week), there has been large week-2 forecast errors of the NCEP GFS ensemble mean ending 11 April. In fact, per

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html ,

week-2 North American ACC scores of 500mb Z anomalies are nearly zero (5-day averaged). I do attribute these errors to not only the west Pacific Ocean signal, but also other dynamical processes explained by the WB (2007) GSDM and WB (2007, 2008) GWO. In any case, I strongly disagree with any statements from whoever or wherever minimizing the impact of the tropical forcing (as discussed above) on the USA (and global) weather during the last 1-2 weeks.

Full disk satellite imagery and all my other tricks indicate the tropical forcing is slowly increasing across the Eastern Hemisphere. Anomalous twin upper tropospheric tropical/subtropical anticyclones are spreading into the Indian Ocean with cyclones getting better defined around the date line. Given the baroclinic structure of these circulation anomalies along with the OLRA, the WH (2004) MJO index has orbited to phase 1. My own feelings are to expect tropical convection to increase across the equatorial Indian Ocean during the next 1-2 weeks while the west central into the southwest Pacific Ocean does “its own thing (the new world atmosphere is still hanging around)”. During weeks 2-4 there may be a significant increase of intense to severe tropical thunderstorm activity centered on western Indonesia.

Global relative AAM remains low (~minus 1.5 sigma through 9 April per R1 climatology) and is probable to stay that way for at least the next few weeks. The global mountain torque is ~minus 10 Hadleys including contributions from both East Asia and the Andes. That component of the earth-atmosphere AAM budget has led to a roughly minus 10 Hadley global AAM tendency. Hence the GWO is strongly in phase 2, and it is probable to do more orbits around phase 3 (GSDM Stage 1) in GWO phase space for at least the next few weeks. This translates to an increase of anomalous zonal mean easterly wind flow in the subtropical atmospheres. Zonal mean easterly wind flow anomalies are already quite large ~25N (roughly 10m/s at 200mb). Hence, keeping in mind the global-zonal mean-regional perspective I take in these discussions, the circulation remains strongly characteristic of La-Nina.

My USA outlooks remain a broken record. As discussed last weekend, circulation anomalies across the PNA sector are probable to retrograde during the next couple of weeks. Zonally oriented RWDs (typical response of a strong “GWO regime”) interacting with increasing Eastern Hemisphere tropical convective forcing will lead to this westward shift. I have been struggling recently with the details. Nonetheless, I do think what many of the latest model runs are showing predicting more western USA troughs then slamming the Plains is reasonable. In fact, given variations in amplitude along with the seasonal northwest shift, this pattern may continue well into May. Weather ramifications for the lower 48 states are “obvious” by now. However, week-1 (next week) should be fairly tranquil due to initially limited moisture transport from the deep tropics through the Gulf of Mexico.

Portions of the central and southern High Plains had some decent precipitation (rain and snow) this past week, particularly eastern Colorado and western Kansas. That was more than I expected. Still, my concerns of prolonged dryness remain for these areas. There are other factors that I can see which could mitigate some of this.

Severe weather internationally (including temperature extremes) appears to have increased a bit during the last week. I continue to leave it to the expertise of the appropriate weather centers internationally to alert the public of these risks.

As discussed above, tropical thunderstorm activity is probable to become quite intense/severe from the Indian Ocean into Indonesia during the next 1-2 weeks, perhaps centering on western Indonesia (roughly 0/120E) by ~weeks 3-4. Whether or not MJO #5 develops is unclear. Locations to be impacted may also include portions of Southeast Asia and the Philippines. There are already a couple of suspect areas for Eastern Hemisphere tropical cyclone development. That risk may increase especially for the Bay of Bengal by week-3. Climatologically, the Bay of Bengal has one peak period of tropical cyclones during May. The west central into the southwest Pacific Ocean remains a “wild card” for at least the next couple of weeks.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing time series of normalized global relative AAM time tendency (Y-axis) and normalized global relative AAM anomaly (X-axis) can be found at

http://www.cdc.noaa.gov/map/clim/gsdm.shtml

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous to the WH (2004) “convention”. In addition, the GWO plot does not have the ENSO signal removed.

Please see the revised description of the GSDM per above link. Also, I encourage the readers to study the annotated MJO and GWO phase space plots to help relate the global variations explained by those techniques to “weather”.

Links to CPC and PSD ENSO discussions:

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

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

The following is a link to information about the stratosphere:

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, a two-part paper is in preparation by WB that will formally introduce the GWO along with subseasonal composites. Given shift work and upcoming travel, updates remain extremely difficult. I am planning on posting another discussion next weekend, 19-20 April.

Ed Berry

Reprisal

This will be a shorter discussion. There have been no significant changes to the global tropical and extratropical SSTs during the past week. Some warming to near climatology has occurred across the equatorial Indian Ocean while equatorial Pacific Ocean La-Nina SSTs remain ~minus 1-2C below normal. SST totals from the Indian Ocean into the Bay of Bengal are approaching 30C while exceeding 30C over much of the west-central and South Pacific Ocean. See links below for additional information:

http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html

http://www.pmel.noaa.gov/tao/jsdisplay/

http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18).

While I am not by any means surprised, the Eastern Hemisphere moist tropical convective forcing discussed a week ago did “unexpectedly” propagate eastward into the very warm southwest Pacific Ocean. Furthermore, tropical forcing increased considerably over the Western Hemisphere particularly from northern South America into central Africa. The latter included an enhancement of the Atlantic Ocean ITCZ.

While some may suggest that this Western Hemisphere signal is simply a convective coupled Kelvin wave, I disagree. Similar to early March, complicated Rossby wave energy dispersion (RWDs) dynamical processes linking the Eastern Hemisphere tropical forcing with the extratropics helped to force the current Western Hemisphere signal. To keep things simple, there has been robust tropical-extratropical coupling during the last few weeks, including a MJO component to the tropical variability (currently phase 8 of WH (2004)). I want to stress the MJO component (and other “things”) are significantly impacting the USA weather (more said below) as I type, and doing so in a manner not expected a week-ago. Any suggestion to the contrary is NOT scientifically defensible.

I am thinking that the Western Hemisphere tropical forcing is “taking over”, and will lead to a rapid intensification of deep moist convection across the currently suppressed Indian Ocean during the next couple weeks. The west-central to South Pacific signal may also persist, lending the possibility of our nemesis of 2 regions of moist tropical forcing for a period of time.

There is a zonal wave number 2 baroclinic circulation response across the tropics, including anomalous twin upper tropospheric anticyclones at ~140E. RWDs from the latter arc nicely to the developing western USA trough, and is consistent with the WB (2007, 2008) subseasonal composites for WH (2004) MJO phase 8. Dynamical processes involving the solid earth-atmosphere AAM budget (not discussed today) are starting to remove westerly wind flow from the global atmosphere. Updated through 2 April (ESRL/PSD R1 data plots), global relative AAM tendency is ~minus 20 Hadleys, with a large contribution coming from the Southern Hemisphere subtropical atmosphere. Zonal mean easterly wind flow anomalies remain well above average (~10m/s at 200mb) across the Northern Hemisphere subtropical atmosphere centered ~25N. These easterlies have actually shifted slightly southward during the last 10 days.

Summarizing the above, the WB (2007, 2008) Global Wind Oscillation (GWO) has orbited to phase 2 having a greater than 1 sigma projection. The MJO component has been “in step” with the GWO recently; however, whether or not that continues is unclear. I do think that more circuits around GWO phase 3 are probable for at least the next few weeks, particularly if our La-Nina base state becomes enhanced.

There are no major changes to my USA outlooks. However, RWDs tied to the MJO west Pacific Ocean signal discussed above is leading to greater meridional trough amplification across the western USA than I discussed a week ago. Many numerical models (ex., ECMWF) and their ensembles, having good initial condition information, suggested this notion at least as early as ~ 1 April. However, I should also mention that the NCEP GFS week-two ensemble mean prediction of 500mb height anomalies ending 5 April suggested an eastern Pacific trough and western USA ridge. I disagreed with this prediction suggesting essentially the opposite phase based on the GWO. However, like the models I did a poor job anticipating the tropical convective forcing to come out into the southwest Pacific Ocean. Hence the current trough digging into the western USA, while expected by me 2-3 weeks ago, is deeper (greater amplitude) than I thought.

As shown by the models for week-1, several synoptic events leading to potentially widespread and destructive high-impact weather are likely for the CONUS. Locations already hit hard by flooding and severe local storms may experience numerous rounds focusing on locations from Southern Plains to Iowa and the Ohio Valley. While bad news for much of the country, locations across the central and southern High Plains may finally get some beneficial precipitation next week. Of course, one or two late season snowstorms with blizzard conditions including intense thundersnow may occur from portions of the Rockies into the Northern Plains.

However, after week-1, status quo appears probable to return for the lower 48 states meaning a northward shifted storm track. As tropical forcing increases across the Indian Ocean, retrogression of existing circulation anomalies is probable week-2 suggestive of troughs just off the USA west coast and central states ridge. That would allow a break in the active regime. Weeks 3-4 are probable to again see more western USA troughs progressing into the Plains/Upper Mississippi Valley (weather ramifications should be understood) but leaving the southwestern High Plains dry. Perhaps the seasonal cycle and maybe even a west Pacific Ocean signal (leading to a strong subtropical jet into the Desert Southwest states) will mitigate some of that.

Severe weather internationally has remained relatively tame during the last week. I continue to leave it to the expertise of the appropriate weather centers internationally to alert the public of these risks.

Intense to severe thunderstorm activity should decrease week-1 across tropical South America while spreading into central Africa and the equatorial Indian Ocean by weeks 2-3. The latter may occur initially south of the equator. By weeks 3-4 moist convection may be very active from the Indian Ocean into Indonesia. The Bay of Bengal may start to have an increased risk of tropical cyclones by week-3. Climatologically, the Bay of Bengal has one peak period of tropical cyclones during May.

The west central into the southwest Pacific Ocean will be a “wild card” for at least the next couple of weeks. Intense thunderstorm activity is probable to hammer portions of the paradise islands week-1 and I can see a scenario of the Philippines getting into the act week-2.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing time series of normalized global relative AAM time tendency (Y-axis) and normalized global relative AAM anomaly (X-axis) can be found at

http://www.cdc.noaa.gov/map/clim/gsdm.shtml

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous to the WH (2004) “convention”. In addition, the GWO plot does not have the ENSO signal removed.

Please see the revised description of the GSDM per above link. Also, I encourage the readers to study the annotated MJO and GWO phase space plots to help relate the global variations explained by those techniques to “weather”.

Links to CPC and PSD ENSO discussions:

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

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

The following is a link to information about the stratosphere:

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, a two-part paper is in preparation by WB that will formally introduce the GWO along with subseasonal composites. Given shift work and upcoming travel, updates remain extremely difficult. I am planning on posting another discussion next weekend, 12-13 April.

Ed Berry