Saturday, June 10, 2006

Getting the Act Together

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 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.

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 frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction.

SSTs have changed little since June 7th. Global SST information can be obtained from latest TAO data here, and ESRL/PSD data here . The following are links to ENSO discussions.

The WH dynamic convectively coupled signal (initiated by a convectively coupled Kw a few weeks ago) has become less coherent during the last several days. Latest satellite imagery shows a NE-SW cloud band across the Caribbean with additional enhancement across northern South America. This cloud band, the result of interactions between the WH signal and a stalled synoptic-scale front, has significantly disrupted tropical moisture transport through the Gulf of Mexico into central Plains during the past week. A tropical depression (TD#1) has developed west of Cuba out of the enhanced frontal convection.

Tropical convection continues to expand and increase across the EH, extending from the equatorial IO into Indonesia. Convection also remains intense from the Bay of Bengal (BB) into SA, and is consolidating with the clusters farther south. The IO development is likely the result of the WH signal coming back around through central Africa, where tropical convection has also been recently enhanced. I think the consolidation process of dynamically forced and boundary forced (latter due to warm SSTs) tropical convection is in progress. The most dominate tropical forcing is already in the EH, and should remain so (with further intensification) for at least the next 1-3 weeks. A MJO may evolve from the large area of forcing.

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

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.

Agreement is better among the statistical and numerical models that the dominate signal of tropical convective forcing will be 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 still 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 (with anomalous convergence), they are stronger than normal from the date line into the IO (anomalies ~ minus 2-5 m/s). AAM anomalies are ~ minus 1.5 standard deviations below the 1968-1997 climatology, with its tendency at about minus 2 standard deviations, 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 The recent increase in the zonal mean anomalous westerly flow across ~25-40N and S (inter-hemispheric symmetry) may be due to eddy feedback and transport processes.

With convection developing across the IO and becoming robust from the east IO into western Indonesia during week 2, the AAM tendency may become less negative (see reanalysis AAM tendency plot ) and perhaps positive as zonal mean anomalous easterlies propagate off the equator into the subtropics (with downward AAM fluxes). Within the framework of the GSDM, contributions to the tendency may include both the mountain and frictional torques (see plot for mountain torque and plot for the frictional torque; see for all AAM plots).

Forecast uncertainty remains much higher than “usual”. Sources include tropical convective flare-ups from other anomalously warm tropical ocean basins such as the North Atlantic and South Pacific, and the roughly 25-day variations of the global mountain torque especially from the Andes Mountains this time of year. While I am more confident about the tropical convective forcing consolidating ~ the western MC during week 2, there is still uncertainty. For instance, should convection literally explode across the equatorial IO during weeks 1-2 and lead to suppression farther east while evolving into a MJO, I may be writing a different tune by my next update. Useful predictions at these ranges within the GSDM framework must be expressed probabilistically with years of solid verification to maximize utility.

Week 1 (11-17 June 2006): A summertime rendition (shorter wavelengths) of GSDM Stage 2-3 best describes the circulation at the start, for at least the PNA sector. A generally split flow pattern should exist along the North American west coast, with a ridge from western Canada into Alaska and a trough along the West Coast into the Rockies. 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 central Rockies into the Plains east-southeast to around Virginia/Carolinas for a couple more days. By the end of this period, strong westerly flow is probable from the Pacific Northwest into the Northern Plains, partly the result of baroclinic wave activity currently coming off of East Asia as it interacts with the intensifying EH tropical convection. The storm track would then shift back to the north (with the “old west coast trough”) while excessive heat returns the Southwest and Southern Plains. Please see for the latest tropical cyclone information.

Week 2 (18-24 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 from the Northern Rockies into Upper Mississippi Valley and the Ohio Valley, while excessive heat continues across the south central states. Other anomalies should be apparent.

Week 3 (25 June-01 July 2006): GSDM Stage 1 would be most probable, perhaps as a summertime rendition meaning a trough along or just off the USA northwest coast (~125-130W)-eastern Rocky Mountain/Central States ridge and East Coast trough. Above average westerly flow would continue from the northern Rockies into the Northern Plains. Depending on the amplitude of the ridge, tropical moisture transport into the southwest states may increase. This whole pattern may start shifting east late in this period.

Cooler and wetter weather is likely for Southwest Kansas for the next few days. By the end of the upcoming week, ~6/15-16 maximum temperatures ~100-110F with gusty southwest winds may occur. There may be some relief next weekend with a STJ (and the northern Plains trough) leading to clouds and at least high based storms along the lee-side trough. Afterwards, just typical summer heat for week 2 with mainly scattered diurnal storms. Precipitation opportunities may increase week 3.

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

I will attempt another posting sometime around the middle of next week.
Ed Berry

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