Thursday, June 22, 2006

Playing a Different Tune

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

The gist is that 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. 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.

SSTs have changed little since my last posting on June 17th. Global SST information can be obtained from latest TAO data here, ESRL/PSD data here, and CPC data

The following are links to ENSO discussions.

Linked to the convectively coupled Kelvin wave that moved from the Western into the Eastern hemisphere a couple of weeks ago, tropical convective forcing has significantly increased across the Indian Ocean (IO) during the last 5-7 days. Per satellite imagery the centroid was at ~5N/90E, and may the largest positive anomalies of tropical forcing observed in that area for at least a year. With widespread negative anomalies of outgoing longwave radiation (OLR) ~minus 70-90 W/m**2 and lower, this region of convection extended from the equatorial IO and Arabian Sea through the Bay of Bengal and western Indonesia and finally into Southeast Asia. A much less intense region of tropical convection was located across the West Pacific, centered at roughly 10N/145E. The latter region was the most dominate until about a week ago.

My thoughts are a true MJO may be developing out of the IO convection, understanding the role of the monsoon systems and seasonal cycle (which does not favor MJOs this time of year). We may be starting to get a SST, tropical convective forcing and global circulation response feedback process going. If this is the case, there will be seasonal forecast implications; for example, the development of a warm event across the central and eastern equatorial Pacific (a.k.a. El-Nino) may become a possibility.

In my last posting I favored a consolidation of the two above mentioned areas of tropical convection, with the West Pacific being the stronger. Instead, the IO convection is taking over, and I may still get my consolidation with a different evolution. Linear (and obvious) thinking would have suggested the latter; that is, going with the dynamical signal instead of the boundary forcing (which my research colleague did favor – the lead author on our paper). So, I am going to play the tune of the IO convection expanding eastward and “absorb” the convection farther east, while propagating east and north as possibly a MJO. By the end of week 2, we may see a spatially tilted structure of tropical convective forcing extending from roughly India east and southeast across Indonesia into the West Pacific, centered ~5-10N/110-120E. How far east this all propagates is a very good question.

A few of the empirical/statistical tools and numerical models support the above; for example, the empirical extrapolated predictions from the time-filtered coherent modes technique and even the NCEP GFS model. However, they are generally inconclusive. Please see ESRL/PSD MJO tools , BMRC MJO tools, CPC MJO tools, and

for the details.

Zonal mean 200mb wind anomalies of ~ minus 10-20 m/s continue to propagate into the subtropical and lower midlatitude atmospheres of both hemispheres, with zonal mean westerly anomalies ~5-10m/s appearing along and just north of the equator. These poleward propagating zonal mean easterly anomalies will favor stronger than normal subtropical ridges across both hemispheres for at least the next couple of weeks. Strong zonal mean westerly wind anomalies (~15-30 m/s; largest in the Southern Hemisphere) still prevail across the Northern and Southern hemisphere extratropics, indicative of inter-hemispheric symmetry due to tropical forcing.

AAM anomalies (largest across the Southern Hemisphere) still remain ~ minus 2 standard deviations below the 1968-1997 climatology, based on the reanalysis data which lags 3 days from the current time. The operational data plot shows AAM has ~ 3 standard deviations below the 1979-1998 climatology (see With contributions coming from particularly the frictional torque and even the Earth component of the budget, the AAM tendency has been positive (links below).

Animations of daily mean 150mb and 250mb vector wind anomalies show that a strong signal of anomalous divergence due to the convection has appeared across the Arabian Sea and much of the IO during the last 3-5 days. Loosely, there are twin subtropical anticyclones in that region (with twin low level cyclones and surface westerlies on the equator – baroclinic mode). About 7-10 days ago twin anticyclones were located across the west Pacific, in response to the tropical SST boundary forced convection. Interacting with the baroclinic wave packets moving through Asia (one of the fast components of the GSDM), there is already a phase reversal of circulation anomalies starting to appear across the extratropical North Pacific ~ 45N/180. About a week ago there was a cyclonic circulation anomaly in that area. In the last few days an anticyclonic circulation anomaly has now appeared there. This is all directly linked to Rossby wave energy dispersion emanating from the IO convection as well as the poleward propagating zonal mean easterly anomalies (discussed above).

Equatorial westerly wind anomalies are becoming more robust globally, with their zonal mean anomalies ~ 5-10 m/s at 200mb. I would like to argue these westerly anomalies are appearing as the result of wave breaking of extratropical baroclinic wave trains/packets interacting with the eastern hemisphere (first the West Pacific, now Indian Ocean) tropical convective forcing, leading to “expected AAM fluxes”. Indeed, there is now a zonal mean momentum sink at ~30N with flux convergence ~ 45N. However, that is an outstanding research issue, and needs attention for both theoretical and prediction concerns. In any case, the appearance of these upper tropospheric equatorial westerly wind anomalies is another one of the components leading to the observed positive tendency in global relative AAM. In very general terms, I would expect the equatorial westerly wind anomalies and AAM to continue increasing during the next couple of weeks particularly if a MJO does evolve.

Within the framework of the GSDM I think we are transitioning to a summertime rendition of GSDM Stage 2, particularly since the frictional torque is positive while the global mountain torque is trending toward positive (see plot for mountain torque and plot for the frictional torque; see for all AAM budget plots, including tendency). The phase reversal of circulation anomalies across the extratropical North Pacific and increasing equatorial westerlies also support that notion. My thought is that the tropical West and Northwest Pacific convection started this change, and now the very intense convection evolving into perhaps a MJO across the central IO may continue this process.

During August of 2004 and 2005 we observed summertime versions of GSDM Stage 2, and that response was a “prolific” heavy rain and severe local storms producer for the middle of the country (along with cooler than normal temperatures). Please see our past weather-climate discussions for details. Given the recent SST behaviors and possible development of a MJO out of the IO convection, perhaps the GSDM Stage 2 response may persist for a few weeks. In the outlooks that follow, while I feel comfortable about transitioning to GSDM Stage 2, my confidence in the synoptic evolution is very low given the appearance of the extremely intense IO convection and its future. As discussed below, whatever the details area, we should see a west and northward shift of the current circulation structure across the Asia-Pacific-North American sector.

Week 1 (23-29 June 2006): Tropical moisture transport from the deep tropics through the Gulf of Mexico into the eastern half of the CONUS is well established. A transition to GSDM Stage 2 is most probable, meaning ridge development from the eastern Pacific into the Alaska with a downstream trough across western Canada and the Pacific Northwest/Northern Rockies by the end of this period. A belt of strong cyclonic westerly flow along and south of the USA/Canada border from perhaps the Pacific Northwest/Northern Rockies topping a ridge extending from the Atlantic into the eastern and southeastern USA would then be expected. Finally, I would also expect a ridge across Desert Southwest, with a cyclonic shear axis/trough in between the two intense subtropical highs. The above described evolution may appear as a slow retrogression and amplification from the current synoptic regime (and anomalies) across the PNA sector. Latest available numerical models indicate an improving trend toward this week 1 prediction (see links below).

Active and possibly severe MCSs/Derechoes (along with areas of heavy rainfall) from the Northern and Central Rockies to most of the Plains and Central states into the Great Lakes and Ohio Valley will be a concern. Additionally, locations from southeast Texas too much of the East Coast may receive locally excessive rainfall. Finally, with the zonal mean anomalous easterly flow propagating into the midlatitudes, that environment would be more favorable for active easterly waves across the Tropical North Atlantic which could undergo tropical cyclogenesis. Please see for the latest tropical cyclone information.

Week 2 (30 June-06 July 2006): GSDM Stage 2 persisting is probable, with Hazards similar to week 1. In this situation areas for excessive heat and humidity may be confined to the Deep South but with synoptic northward excursions. The Desert Southwest monsoon may remain suppressed due to the Pacific Northwest trough.

Week 3 (07-13 July 2006): GSDM Stage 2, possibly transitioning to Stage 3 (need to leave this possibility open), would be my best offering. Should we see Stage 3, it is probable the Upper Mississippi Valley and Great Lakes would have below normal temperatures with warmth across the Pacific Northwest and Inter-Mountain West. Roughly the eastern half of the country would be wet.

Loosely, Southwest Kansas may see several rounds of MCSs/clusters of thunderstorms for at least the next couple of weeks. Temperatures should average out near normal. Maximum temperatures may vary from around 100F on the dry days to upper 60s and 70s during post frontal/MCS days. Hopefully this situation will persist into week 3 given the past extended period of dryness. This outlook and all the discussion above only support my following assertion, already stated in past postings. I do not think our weather-climate situation supports an extended period of tremendously excessive scorching apocalyptic heat with no rainfall, for at least the next month (and maybe the rest of this summer).

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 (animations of various fields from the operational data) (Global Tropical Hazards Assessment available from this site, along with other useful information)

Latest CDC Ensemble Forecast

Latest NCEP Ensemble Forecast

Additional NCEP Ensemble Output

Latest Canadian Ensemble Output

Latest Deterministic ECMWF Forecasts (link to our Weather-Climate discussions)

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 this upcoming weekend.
Ed Berry

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