Saturday, January 03, 2009

La-Nina well Entrenched -- PNA Retrogression Likely ~Days 10-20

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

Please keep in mind the ESRL/PSD GSDM web link, below, while reading this discussion.

The 91-day signal to noise ratio (snr) anomaly composites are being updated daily. There are still map room issues that are being worked on. WB (2009), part-1 of a 2 part paper where the GWO is formally introduced, is in press for MWR publication. There is a link in the Appendix to download the manuscript.

These discussions are a component of an experimental effort involving linking weather and climate. We are moving forward on plans for having a one-day workshop in Boulder on 24 February 2009 discussing the WB (2009) GWO. Our announcement is forthcoming; stay tuned.

The spatial pattern of global SSTs is unchanged (see links). There has been ~1C cooling across the southwest Pacific Ocean during the last week (due to intense frontal (SPCZ) rainfall) with slight warming across the Indian Ocean. In fact, significant warm anomalies (~2C/~29C totals) are present over the southwest Indian Ocean in the region of Madagascar.

Substantial negative SST anomalies (~1-2C per 5-day averaged TAO buoy data) are present along the equator (within 5 deg lat) from 160E to the coast of South America. These cold anomalies are deep, extending to ~200m depth east of 160W, with magnitudes ~minus 5C. This subsurface is similar to a year ago, meaning a steeper than normal oceanic thermocline that is typical of a mature basin wide cold event. While we expected a La-Nina encore as early as late September 2008, the magnitude of the cool SST anomalies across all Nino regions has exceeded my expectations. Again, this is a response to the global ocean-land-atmosphere dynamical system (the WB (2009) measure of the GWO attempts to represent some of this), and is not good news for (example) probable drought prone areas in this situation (such as USA southern and central High Plains). (note the initial projection) (link 18)

The issue of wind and tropical convective signals syncing up continues. Since October 2008 there have been 4 coherent episodes of when these signals “faded in and out” in terms of coupling. Taking into considering numerous time-scales involving complicated feedbacks that I will not discuss in an inefficient manner such as these blog writings, the periodicity has been ~30 days. After the large (~3 sigma) October and November GWO orbits in phase space involving octants 4-5 to 8-1 then 4-5, a weaker rendition occurred from roughly 8-18 December leading to the current variation. Updated through 1 January 2009, the WB (2009) measure of the GWO was in ~octant 4 of phase space. Each one of these orbits in GWO phase space has been seemingly spiraling toward octants 2-3, the La-Nina attractor for our purposes.

There is no coherent MJO, which has been the case since the truncated October 2008 spatial variation of tropical rainfall anomalies projecting onto this mode. Starting during November, a general consolidation ~0/120E of intense to severe tropical thunderstorm activity has been in progress. Updated through 1 January 2009, retaining the very important interannual and ENSO signals, the WH (2004) measure of the MJO had nearly a 2 sigma projection in octant 5 of phase space. This is, in reality, a quasi-stationary La-Nina mode of tropical forcing centered on Indonesia, and it does appear the wind signal is trying to get back in line. Phases 4-5 of both the GWO and MJO 250mb psi composite anomaly plots loosely depict the extratropical and tropical circulations, respectively.

Per animations of upper tropospheric daily mean vector wind anomalies, the flow of wave energy tied to the ~8-18 December variation can be observed coherently propagating into the Eastern Hemisphere subtropical atmospheres just before Christmas. That led to strong meridionally directed Rossby Wave energy dispersions (RWDs) into the extratropical Northern and Southern Hemispheres leading to poleward shifting of anomalous zonal mean easterly wind flow (to ~45-60 N/S). Zonal mean equatorward flux convergence of AAM increased ~40N around this time (loosely) leading to an acceleration of westerly wind flow at that latitude. Synoptic responses have included strong North Atlantic Ocean blocking (an example of why the NAO is red noise) and a retracted Northern Hemisphere polar vortex. In fact, the latter may explain the recent anomalous cooling in the stratosphere.

Baroclinic wave energy associated with the ongoing GWO orbit is currently propagating into the Eastern Hemisphere, interacting with the circulation anomalies discussed in the previous paragraph. Similar to the November 2008 GWO orbit (~40 days ago), a positive global mountain-negative frictional torque index cycle variation is occurring (see AAM plots). The positive mountain torque has a large contribution from East Asia, ~20 Hadleys. Fighting the La-Nina base state, a poleward shifted extension of the East Asian/North Pacific Ocean jet is occurring as I type. All models have captured this jet, and correctly predict a positive phase of the PNA teleconnection by late week-1.

The last 2 paragraphs were written to show an example of a forcing-response-feedback loop linking global to zonal mean to regional-scale circulation anomalies. The WB (2009) measure of the GWO, lined up with the tropical forcing, is probable to orbit into octants 8-1 of phase space during the next 1-2 weeks. Observe that in spite of a ~30 Hadley calculated positive AAM tendency, global relative AAM is still below the R1 data climatology (after a 3 sigma decrease from November). Hence, perhaps similar to early-mid December, any ridge from Hell that may evolve along the USA west coast is likely to retrograde after day 10 as the North Pacific Ocean jet retracts. The ridge may shift back to ~150-160W by roughly week-3, and possibly allow cold troughs to dig along the west coast. Models already are, and will continue to play “catch-up” to this situation. My confidence is at least moderate with this notion, given our well defined La-Nina global circulation involving Eastern Hemisphere tropical forcing and strong meridional symmetry of zonal mean and regional circulation anomalies.

Phases 4-5 of the GWO snr 250mb psi composite anomaly plots are probable to depict the extratropics week-one followed by 8-1-2 by late week-two and week-three. Whether or not we lock-in to a superposition of GWO and MJO circulation anomalies shown by ~phases 2-3 of the 250mb snr psi (and temperature) composite anomaly plots for a JFM mean is still unclear. Regardless, a La-Nina situation of at least repeated progressive troughs into the western and central USA is probable. That may be along a northward shifted storm track favoring southwest flow across the Plains. Arctic air may focus from the northern and central Rockies into the Plains and Upper Mississippi Valley. Again, there will be variations due to feedbacks.

Weather ramifications including additional high impact weather should be well understood. In fact, the JFM 2009 seasonal mean outcome for temperature and precipitation is likely to have some similarities to JFM 2008. While anomalous wetness is probable from the Pacific Northwest into the Ohio Valley, significant/severe drought conditions may re-emerge for locations such as the central and southern High Plains (including western Kansas) by boreal spring. I had some optimism during fall the latter would not occur, and hopefully there will still be decent precipitation.

Intense to severe tropical thunderstorm activity is probable to persist from Indonesia into at least northern Australia “UFN” (centered ~120E), slowly shifting south. Locations around the SPCZ and tropical South America are likely to have some enhancement week-1, and anomalously intense rainfall may return to South Africa and particularly the South Indian Ocean weeks 2-3. The latter may merge with the quasi-stationary enhanced Indonesian/Australian convection. I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide, including official statements for tropical cyclones that may impact regions such as around Australia and Madagascar during the next several weeks.


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. We hope that an opportunity will arise for us (soon) to allow our dedicated web page effort to mature, expediting objectively and accountability. This web page effort will hopefully include an objective predictive scheme for the GWO with hindcasts.

The WB (2007) paper on the GSDM has been published in the February issue of MWR. The first of a two-part paper, where WB formally introduce the GWO (WB (2009)), has been accepted for publication MWR. A pdf of the in press version can be downloaded from the following link:

In addition to the subseasonal snr composite anomaly plots, we hope near real-time discussions with “weather maps” will become a routine part of the ESRL/PSD GSDM web site sometime soon. Part-2 of our GWO paper will discuss the latter. 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, in addition to a climate service for all users. Relying on the numerical models alone is a cookbook! I plan on posting a discussion the weekend of 10-11 January 2009.

Ed Berry


Carsonspotter said...

Hi Ed.

I have been following your discussions for some time and I really appreciate reading them with long range weather forecastng. Having said that, I just read your latest discussion about the possible return to a cold troughy type pattern again by week 3. I am concerned with the last two very dry winters in California and Nevada, that we may be repeating the same thing again this winter. While it's nice to see the cold snowy patterns at times, it just doesn't seem to do much for the Sierra snowpack give or take a storm or two so far this winter. Do you see any potential for any high impact weather events for the two states mentioned above? My feeling this winter as you mentioned, will be similar for the JFM, which was rather dry but cold with the exception of the very strong storm that affected the area in early January 2008 (this was basically only real significant storm for the cold season). After that it was below normal precipitation wise in spite of the cold trough pattern. February and March last year were rather non-existent precipitation wise for both states (alot of wind to add). A possible 3rd year of drought? Hopefully not. At any rate, keep up the good work. I enjoy reading these discussions and your contributions to the HPC/ESRL testbed projects.

Many thanks.


Ed Berry said...

Hello Robert,

Thank you for the comment and interest in these discussions! I do agree with your concern. The dry southern USA La-Nina signal appears to be emerging. Other possibilities do exist such as both the IO/Australia and SW Pac regions becoming convectively active later this month (similar to late Jan/early Feb 2008). That could improve precipitation chances for the SW states.

Regardless, anomalous dryness for S. Ca and NV appears to be the most probable JFM outcome. I do not see from my "crystal ball" any major precipitation events for the above locations through at least week-2.

Best regards,

packattack said...

Hi Ed,

I live in southern California and am hoping for a return to a -PNA pattern like mid-December. I got excited when I heard that you think the high will retrograde back into the pacific like it did in December. I guess my question is, when do you think the models will start to pick up on the retrogression of the ridge (so far the GFS has yet to show anything other than the huge ridge progressing very slowly to the east and flattening) and do you think we have a shot at another rainy/cold pattern developing here like we had from 12/15-12/25 of 2008? We really need the rain badly and this blog entry gave me hope again. The model runs keep showing a monster ridge and +PNA and never progress into a west coast trough pattern for any of the west coast by hour 384 on most runs but I remember the same models struggling to depict the retrogression in December as well.

Thanks for your time. God Bless.

Ed Berry said...

Hi packattack,

There is no change to the retrogression scenario I discussed. I did, however, underestimate the ongoing perturbation that is destructively interfering with our La-Nina base state (which may cause a delay).

The +PNA response is directly linked to the intense/severe tropical forcing currently across the SW Pac/SPCZ. Unlike I stated in this posting, a weak MJO component has emerged, and is propagating into the Western Hemisphere. However, by weeks 2-3 the GWO and any MJO component are likely to sync up ~80-120E including the tropical forcing. PNA retrogression should occur by that time. That will help to "reload" La-Nina. In fact, the recent ESRL/PSD ensemble is trying to capture PNA retrogression at ~336 hours.

As you say, this would suggest cold troughs to impact California. I hope there can be at least some Pacific Ocean tropical moisture transport into these systems to increase precipitation. I also hope that my best offering based on our science works out.

Take care,

Brian in Bellingham said...

Ed, thank you for answering questions from laymen like me.

You certainly called the arctic outbreak for the west/PNW way before the models saw it, I think you saw it in middle November, so I really value your opinion.

In regards to cold troughs in the west in late January or eary February, do you have any thought as to how cold the arctic air could be, in comparison to the December events?

I know some forecasters think that the December pattern will repeat, and that the arctic air would be stronger then any time this winter, which is saying a lot considering the cold that Seattle had in December and the midwest will have next week.

Ed Berry said...

Hello Brian,

Thank you for the kind comment. As you know, it is difficult to say exactly what the strength (in terms of anomalies) the Arctic airmass will be should it impact the Pacific Northwest by later this month. However, there is a respectable source from Western Canada to Siberia. The gist is that should a regime similar to December return, the weather ramifications are likely to be similar.

Best regards,

snoman said...

Hi Ed,

It's beginning to look like you may be right again. The models are certainly beginning to pick up on the retrogression of the Western rdige. In fact the ECMWF shows it happening before day 10. That seems hard to imagine, but you never know I guess.


Ed Berry said...

Hi Jim,

Thank you for the comment! Please see my latest posting. Retrogression is appearing more likely.


Anonymous said...

Forms ProcessingWith a number of forms passing through an office everyday, it can be time consuming and tiring to take care of all the form processing. Instead of relying on human help, you can quickly accomplish your task with forms processing automation. Pages and pages of written or computerized data and are converted into an electronic form that is convenient for use with forms processing.