Thursday, May 15, 2008

Very Short Update -- Some Just do not Get It!

The following are links to global SST and related information. The interannual component (including ENSO) is unclear and only monitoring will tell. Stay tuned. (note the initial projection) (link 18).

Full disk satellite imagery shows tropical convective forcing literally breaking up into tropical cyclones from the Bay of Bengal into the Northwest Pacific Ocean. Thunderstorms are increasing from the East Pacific ITCZ all the way to western Africa, while the Indian Ocean remains suppressed. As demonstrated by the WH (2004) phase space plot, a robust (not weak, per official sources) MJO (can be viewed as a “component” of the WB (2007, 08) GWO) signal is propagating into the Western Hemisphere and the tropical forcing is responding. The MJO, working with dynamical processes explained by the WB (2007, 08) GWO, has resulted in an increase of global relative AAM (updated through 13 May) too slightly above the R1 data climatology. A zonal mean response has included a fundamental shift of tropical/subtropical circulation anomalies leading to twin anticyclones just west of date line. Regionally, an anomalous extension of the East Asian jet has occurred (wind speed anomalies ~50m/s at 250mb) supporting a ridge (from Hell) along the North American west coast (strong positive phase of the PNA for this time of year).

The first point to make is that MJO variability is currently strongly impacting North America, and will continue to do so for ~weeks 1-3. Any statement to the contrary is scientifically not defensible. Secondly, I am quite confident that tropical convective forcing will return to equatorial Africa and the Indian Ocean (west Pacific Ocean nemesis understood) during weeks 2-3. Sparing the “dynamics lesson”, the GWO is probable to collapse to octant 1 then orbit in phase space to octant 3 during the next few weeks. The physical processes responsible (ex., surface torques and AAM transports) will remove zonal mean westerly wind flow (anomalies ~5-10m/s at 200mb) from the tropical and subtropical atmospheres. In fact, the El-Viejo base state may get rejuvenated during the next few weeks. The latter suggests a return to anomalous twin tropical upper tropospheric anticyclones (cyclones) in the region of the Indian Ocean (date line) and perhaps another Branstator (2002) circumglobal teleconnection of midlatitude ridges.

For the USA the above means the anomalous North Pacific Ocean jet is probable to collapse into an energetic western states trough by week-2 leading to a southwest flow storm track on the Plains. This situation may persist through weeks 3-4, shifting northwest with the seasonal cycle. The notion of this retrogression has already been discussed in past postings.

Official forecasts have not yet picked up on this (at the time of this writing), being fooled by model disagreement, etc.. This again demonstrates the need of an atmospheric dynamics based weather-climate linkage framework to intelligently evaluate numerical model guidance (insert my angry Rottweiler)! One purpose of the WB (2007, 08) GWO is to facilitate the latter. There is no cookbook to making subseasonal forecasts, and that includes blending numerical model predictions!!! Ensemble prediction schemes such as from ESRL/PSD as well as the deterministic ECMWF model have provided the most realistic solutions for the USA. Link below is verification for the GEFS. .

The final point is that a potentially explosive pattern for severe local storms on the Plains exists for at least week-2 (exact timing is white noise). Locations to get hit the hardest may be farther north than observed during the last few weeks (climatology understood). The latter may extend from portions of Oklahoma into Iowa then into the Ohio Valley. Late season heavy snow (with intense thunderstorms) may also pound portions of the Rockies. While the western states cool down, the southeast should warm to above normal. Other weather ramifications should be well known by now. The latest official week-2 forecast for the USA does not indicate the latter, and I strongly disagree based on scientific reasons.

Locations from portions of the Bay of Bengal into Indonesia/Southeast Asia and the Philippines are still likely to get hammered with intense to severe thunderstorm activity week-1 including tropical cyclones (please see JTWC). This activity is probable to weaken weeks 2-3 as tropical thunderstorm activity increases from Africa into the Indian Ocean. By weeks 3-4 intense-severe thunderstorm activity may extend from the Arabian Sea into Bay of Bengal and Southeast Asia.

The best shot for enhanced Western Hemisphere convection, impacting northern South America into the Atlantic ITCZ appears to be weeks 1-2. I trust the expertise of the appropriate weather centers internationally 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. 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:

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 for variables such as surface temperatures. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships.

Given shift work and travel, updates are extremely difficult. I should be able to post another discussion the weekend of 24-25 May.

Ed Berry


Paul Sirvatka said...

Wow...where I do not understand much of what you say, I am glad you bring in the physics behind making these extended forecasts. I cannot see how the models going crazy with the ridge /trough dilemma in the southwest should give anyone a 4 out of 5 confidence level. I also do not know what scientific basis there is for using 10% of the GFS operational, 40% of the Mean, 45% of the operational ECMWF and 5% some other nonsense. I just do not know how one makes these decisions.

I think this is one important topic for future forecasters to understand! Thanks Ed for your atmospheric insights!

Paul Sirvatka

Paul Sirvatka said...
This comment has been removed by the author.
mcrowther said...

Hey Ed, Matt C here. I, like Paul
do not totally understand your methods, but looking at he latest
operational guidance all of the deterministic models are now coming around to your forecast. I actually used your confidence in the pattern to take a flyer on a flight to the Plains next Friday.

If I am in DDC maybe I can drop by the office.

Matt Crowther

Ed Berry said...

Hi Paul,

Thank you for the comment! Klaus and I are working on a two-part paper (likely for MWR) that we hope will communicate what the GWO is, along with composites. The latter should help forecasters get a better feel for the subseasonal synoptic evolutions. An important point is to have a complete forecast process that includes a diagnostic weather-climate linkage framework and the models are only a component. Hopefully we will have a web page with "everything" on-line, along with more frequent ~week 1-4 predictions. Stay tuned!

Ed Berry

Ed Berry said...

Hi Matt,

Good to hear from you! Thank you for the comment. You can see the comment I left for Paul. We are seeing a good example of the models catching up to the atmosphere. The deterministic ECMWF and the PSD ensemble were one of the first models to catch on, even out to ~day 10 for the EC.

We felt confident this upcoming retrogression was likely nearly a couple of weeks ago based on the MJO/GWO. What adds confidence is when the models start to give solutions consistent with our atmospheric dynamics based weather-climate linkage framework.

Look forward to seeing you if you are in DDC!


mcrowther said...

Ed, one thing that does worry me about this upcoming pattern- could the amplification in the EPAC be so pronounced that the trough will end up digging too far west for a really good Plains severe outbreak? To me that seems like the main "fly in the ointment" that could ruin my upcoming chase trip. The new Canadian SEF shows this, and I have noticed in the past with this type of retrogressive pattern that we sometimes end up with a closed low near CA and ridging in the Plains.

Ed Berry said...

Hi Matt,

Obviously there are issues with the unpredictable details. However, while the large amplitude notion appears correct, I do not think it is probable for the trough to dig along the west coast. For all the reasons the trough digging into the Rockies is reasonable leading to several days of severe storms on the High Plains. This pattern should shift east loosing amplitude with more western states troughs probable ~weeks 3-4. Of course, there will be a northwest shift with the seasonal cycle.