Saturday, June 28, 2008

Return of the (USA) Wicked Ridge from Hell

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”

I want to shorten these discussions (and still failed). There has not been any change in the overall spatial patterns of tropical and extratropical SSTs. The following are links to SST information, including an ENSO posting by the WMO. As stated by the latter, careful monitoring (including subseasonal atmospheric variability – my part) is critical during the next several months for the future of ENSO. Again, I emphasize that I am discussing the interannual aspect of coupled ocean-land-atmosphere variability where ENSO is a component. (note the initial projection) (link 18)

Full disk satellite imagery shows multiple regions of enhanced tropical convection. Loosely, these are centered from the equatorial western Indian Ocean into the Eastern Hemisphere monsoon systems, the west central Pacific and in the region of the Americas. Hovmoller plots and other diagnostic tools show there has been a slow eastward shift of tropical convective forcing since early May. Per WH (2004) phase space plots, a MJO component of this forcing is present, currently in octant 8 ("Western Hemisphere and Africa").

The extratropics have contributed to the eastward shift of tropical convective forcing. Included are north-south mountain massifs, having broadly positive global mountain torque events of ~20 Hadleys late May, mid-June and most recently. The latter involved the Southern Hemisphere mountain ranges such as the Andes and those over Antarctica. The tropical forcing and stochastic mountain torque events are some of the subseasonal dynamics captured by the WB (2007, 08) GWO.

Complicated interactions of processes briefly mentioned above have worked to add westerly wind flow to the global atmosphere. For example, zonal mean westerly wind flow anomalies of ~5m/s have shifted off the equator into the Northern Hemisphere subtropical atmosphere. There was also a (very) slight transient reversal of upper tropospheric tropical circulation anomalies across the Eastern Hemisphere a few days ago (~24 June), with twin cyclones trying to evolve in the region of the Indian Ocean along with downstream anticyclones. Hence the WB (2007, 08) GWO orbited in phase space to octant 5 on 22 June, before collapsing. Including the westerly QBO phase of the stratosphere, global relative AAM through 26 June was near the R1 data climatology. However, I do expect to see relative AAM decrease (abruptly like the USA stock market???) during the next few weeks.

There is evidence of some tropical-extratropical coupling returning. The WH (2004) MJO and WB (2007, 08) GWO plots are starting to line up in phase space; ~ octants 8-1-2-3 are probable during the next few weeks. Support for this notion includes a negative global frictional torque (~10 Hadleys – GWO component) and a few predictions (ex., POAMA and ECMWF) of the WH (2004) RMM index to orbit to phase 3 by week-3. Physically this means a return to a La-Nina base state and/or a re-enforcement of a stationary low AAM regime that has been present for at least the past year. Seasonal implications are still unclear. The point is that the atmosphere is orbiting in phase space around what may still be the “La-Nina attractor”. This evolution is the foundation for subseasonal predictive information offered below.

In my last posting I suggested a western/northwestern USA trough for the upcoming week. Instead, the wicked ridge (from Hell) of the western USA is returning. Based on subseasonal composites currently being developed, similar to July 2007, anomalous summertime ridge conditions for the western states are probable during phases 3-4 of the GWO. Like that observed during boreal winter 2007-08, these same phases of the GWO favor a western USA trough during the cold season given wavelength considerations (still the season of the witch leading to the wicked ridge of the west?). Based on these composites and rigorous daily monitoring, I had indications of my poor assessment 2 days later. A dedicated web page effort where these subseasonal composites and other tools are available would have greatly facilitated an update.

As all models now show (the GFS has been playing catch-up), an amplified western USA ridge and eastern states trough is likely week-1. I do think this ridge will expand into the central states and Deep South ~week 2, before possibly re-amplifying west of Continental Divide weeks 3-4 allowing a trough in the region of the Mississippi Valley. Thus intense western heat may briefly expand into portions of the eastern USA week-2 after a cool week-1. There will be an active MCS storm track along the “southern edge of the westerlies” focused at times on the mid and upper Mississippi Valley states ~weeks 2-3. The "Desert Southwest monsoon" may get off to a robust start during the next couple of weeks, much like climatology suggests. Other ramifications should be understood.

Intense to severe tropical thunderstorm activity is probable to increase from the Indian Ocean into the monsoon and frontal rain band systems of India and Asia weeks 2-3 while the west and northwest Pacific Ocean is sporadic. The East Pacific Ocean tropical cyclone hazard should wane during week-2. I would have a greater concern for cyclones across the tropical Atlantic Ocean basin weeks 1-2 if it were August-September. Please see the latest official tropical cyclone forecasts for all basins.

Other severe/high impact weather continues internationally. I trust the expertise of the appropriate weather centers to alert the public of additional weather hazards worldwide.


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

This phase plot is being re-done, as is the web site. Stay tuned. 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 -- which will be revised again (work in progress)!!!. 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:

The following is a link to information about the stratosphere and other nice monitoring tools:

The following is a link to NCEP model verifications (surf around for lots more) .

The following is a link discussing recent global weather and related events.

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. This web page effort would hopefully include an objective predictive scheme for the GWO, including hindcasts.

The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, the first of a two-part paper has been submitted to MWR where WB formally introduces the GWO. A pdf version can be downloaded from the following link

Overlapping seasonally varying subseasonal composites for variables such as surface temperatures and streamfunction anomalies are planned on being posted on the web site mentioned above and presented in part-2 of our paper. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships. An important purpose is to provide a dynamical weather-climate linkage framework to evaluate the numerical models in a sophisticated manner as part of a subseasonal (and any time scale) forecast process. Relying on the numerical models alone is a cookbook!

Given shift work and travel, updates are extremely difficult. I hope to post another discussion the weekend of 4-6 July.

Ed Berry

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