Wednesday, June 07, 2006

The Atmosphere is Confused

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

To get the most from these postings, I kindly recommend that at least some perusal of our paper be given. The gist is from taking into consideration the interactions of 4 different subseasonal time scales, a sequence depicting a coherent set of repeatable events has been derived. 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.

Also, I am making attempts to shorten these postings for a variety of reasons. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequently to provide additional detail while having a more complete weather-climate record of attribution and prediction.

With the exception of a cool region just off the coast of South America, a relaxation of trades (due to an oceanic Kw) across the central and east equatorial Pacific has resulted in an increase of cold tongue SSTs during the last couple of weeks. SSTAs vary from ~ plus .5C near 120W to even 1.5C west of the date line, with SSTs from ~22C at the South American coast (anomalies roughly minus 3C) to around 31C just south of the equator at 160E. At depth, as has been true for roughly a month, anomalies around plus 1-2C extend from 50-250m east-west along the equatorial cold tongue, meaning a slightly deeper than normal oceanic thermocline. SSTs of 29C and higher also extend from the southwest Pacific into the IO.

Latest prediction from CPC expects ENSO-neutral conditions to prevail during the next 3-6 months. Global SST information can be obtained from latest TAO data here, and ESRL/PSD data here . The following are links to ENSO discussions.

There are conflicting signals in regard to the tropical convective forcing. Interactions between behaviors such as the early onset of the Indian and Southeast Asian (SA) Monsoons (moist phases), other tropical convective variability, forcing from the extratropics, etc., are a few of the contributors. Per several monitoring tools such as time-filtered coherent modes and velocity potential Hovmollers, the dynamically forced convectively coupled signal is over the WH centered ~40-60W (which did contribute to the East Pacific oceanic Kw), while a boundary forced component (due to warm SSTs) remains from the Bay of Bengal east-southeast into Indonesia and the Southwest Pacific Ocean.

My feeling is the WH signal will propagate well into the EH and excite tropical convection across the equatorial IO during the next 1-2 weeks. This would be consistent with the ~30 day variability of tropical forcing that has been observed since about early December 2005. I also think the convection particularly from SA into Indonesia will persist, with an eventual consolidation of all this tropical forcing (the dynamic and boundary components) in the region of the Maritime Continent (MC) by ~ weeks 2-3. Afterwards, a MJO may evolve and propagate into the warm SSTs of the west and northwest Pacific Ocean.

The time -filtered coherent modes Hovmoller plots of OLR and OLRA are at, velocity potential Hovmollers at , and an animation of velocity potential overlayed on OLRAs are at

Real-time satellite imagery presents strong tropical convection along the ITCZ from the East Pacific into western Africa. Deep moist convection also persists from the Southwest Pacific west-northwest across Indonesia into the Bay of Bengal. Suppression exists elsewhere across the tropics and subtropics. Satellite imagery and other information can be found from the following links: eastern hemisphere, full-disk west Pacific, mtsat, IO, Africa, ; other imagery here. Latest tropical cyclone statements can be found from, while the latest 3-day averages of OLR totals and anomalies and other data can be found here.

There is some agreement among the statistical and numerical models that the WH dynamically forced tropical convective signal will emerge in the EH during week 2, as discussed above. Please see ESRL/PSD MJO tools , BMRC MJO tools, CPC MJO tools for the details.

A time-latitude section of 200mb zonal mean zonal wind anomalies indicates anomalies of ~ minus 5-15 m/s from 15S-N, with the larger anomalies south of the equator and across the WH. Other plots show that while the trades are relaxed with even actual surface westerly flow from the East Pacific into the western Atlantic, they are stronger than normal from the date line into the IO (anomalies ~ minus 2-5 m/s). Finally, animations of 150mb and 250mb daily mean vector wind anomalies loosely suggest twin subtropical anticyclones across the Pacific Ocean east of the date line. A strong baroclinic wave energy dispersion coming off of Asia interacting with these anticyclones is leading to amplification across the PNA sector as I type. This will result in the large anticyclonic circulation anomaly across western Canada by this upcoming weekend as predicted by most numerical models (models have been catching up).

AAM anomalies are still ~ minus 1 standard deviation below the 1968-1997 climatology, with its tendency at roughly zero, based on the reanalysis data, which lags 3 days from the current time. The operational data plot shows that AAM has decreased to 2 standard deviations below the 1979-1998 climatology (see
With some recent increase in the zonal mean anomalous westerly flow across the extratropics, the current AAM tendency may be slightly positive. However, should convection develop across the IO during week 2 as discussed above, the AAM tendency may become negative (see reanalysis AAM tendency plot ).

Within the framework of the GSDM, contributions to that negative tendency may include both mountain and frictional torques (see plot for mountain torque and plot for the frictional torque; see for all AAM plots). Physically, we would observe the present upper tropospheric tropical and subtropical zonal mean anomalous easterlies to propagate poleward (and downward) and be replaced by westerlies.

About 10 days ago I could comfortably state that GSDM Stage 1 best described the global weather-climate situation with respect to forcing-response considerations involving SSTs, tropical convection and circulation anomalies. With the dynamical signal in the WH and the other observations discussed above, a loose GSDM Stage 2-3 situation may be more accurate. This would not be too surprising given the outlooks I made 2 weeks ago valid for this time. However, I did not expect to see the current WH signal. I was expecting a slowly evolving and coherent eastward shift of the tropical convective forcing from the Arabian Sea/North IO into the MC region. In consideration of that and the other components of the GSDM, I was predicting a “clean” GSDM Stage 1-2 transition.

Forecast uncertainty remains much higher than “usual”. Sources include tropical convective flare-ups from other ocean basins such as the North Atlantic and the roughly 25-day variations of the global mountain torque, especially from the Andes Mountains this time of year. I am also unclear just exactly how the tropical convective forcing is going to evolve. For instance, should convection literally explode across the equatorial IO during week 2 with suppression to the east, and evolve into a MJO, I may be writing a different tune during that time. Useful predictions at these ranges within the GSDM framework must be expressed probabilistically with years of solid verification to maximize utility.

Week 1 (8-14 June 2006): A GSDM Stage 2-3 is most probable. For the PNA sector that would suggest a summer-time version (shorter wavelengths) of generally split flow along the North American west coast, with a ridge from western Canada into Alaska and a trough along the West Coast into the Rockies. The latter may project onto the positive phase of the PNA teleconnection, at times. Additionally, I would expect anomalous cyclonic flow from eastern Canada toward at least the Northern Plains/Great Lakes states. This all translates to a stronger than normal jet stream across the northern and central part of the CONUS, with the possibility of active MCSs/Derechos and other severe local storm exotica (and heavy rainfall) from the northern and central Rockies into the Plains east-southeast to around Virginia/Carolinas. Heavy rainfall may also occur across portions of the Northeast. Excessive heat may be suppressed to the Southwest and Southern Plains while fall-like temperatures may be experienced across much of the northern USA from coast-coast. Finally, there may be a tropical cyclone concern for the Bay of Campeche and portions of the Gulf of Mexico (see for latest information).

Week 2 (15-21 June 2006): GSDM Stage 4-1 would be probable if the tropical convective forcing plays out as discussed above. For the PNA sector, that would suggest amplification of a ridge across the central Pacific Ocean leading to a general West Coast trough with a ridge across the central into eastern part of the country. I would expect a trough to linger along the East Coast. That would continue an active MCS track across particularly the Northern Rockies into the Ohio Valley, with the severe local storm hazard, while heat builds across the south central states. Other temperature and precipitation anomalies should be apparent.

Week 3 (22-28 June 2006): GSDM Stage 1 may emerge, perhaps as a summertime rendition meaning a trough along/off the USA Pacific Northwest coast (~120W/130W)-eastern Rocky Mountain/central/southeast states ridge and trough along/off the East Coast. That would favor a continuation of an active storm track across much of the northern CONUS.

After a few days of maximum temperatures ~100 deg F and little rainfall, cooler and wetter weather is probable for Southwest Kansas starting ~6/11. Several nights of MCS activity (including heavy rainfall and severe local storm concerns) may be a good bet going into week 2. Maximum temperatures may drop into the mid 70s-mid 80s for a couple of days. Summer heat and dryer weather returning by next weekend would then be the scenario. Again, for at least the next 2-3 weeks, I do not think we will have a pattern of persistent excessive heat and no rainfall.

Latest CDC Ensemble Forecast

Latest NCEP Ensemble Forecast

Additional NCEP Ensemble Output

Latest Canadian Ensemble Output

Latest Deterministic ECMWF Forecasts

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 offers additional insights not only for possible week 1 high impact weather, but week 2 as well.

I will attempt another posting sometime this upcoming weekend.
Ed Berry

1 comment:

Eric said...

Hi Ed,
Eric from TPC. I'm glad we decided to go with the above average chance of TC genesis in the BOC for week 1. The models have caught onto your thinking and now it looks increasingly likely that something will happen over the weekend (late). Note Africa is really getting going tonight... is the MJO finally trying to make an excursion into the Indian soon?? I wish the BOM or CPC pages would update with the latest OLR info.

The trades have started to kick into the equatorial central Pacific so that should end the El Nino warming fairly soon. I enjoy the blog greatly!