Saturday, February 07, 2009

Deep in the “Strange Brew” of La-Nina and SSW; Several Rounds of USA High Impact Weather are Likely Weeks 1-3

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.

Map room issues continue and are being worked on.

Please see links below for SSTs. Strengthening trades during the last week has renewed cooling of SSTs across all Nino regions. TAO buoy data show 5-day averaged anomalies ~minus 1-1.5C along the equatorial Pacific Ocean cold tongue, with the 29C total SST isotherm back to near 160E. Our downwelling oceanic Kelvin wave (~150m depth) may be loosing some coherence as it propagates into the east Pacific. SSTs have also cooled across the west central and Southwest Pacific Ocean with totals generally less than 30C. The latter is likely a response to the recent strong tropical convective flare-up ~10S/160E about a week ago. (note the initial projection) (link 18)

The global weather-climate situation is extremely complicated. While I do feel comfortable with any diagnosis I can offer, this medium of communication is not a good facilitator. From my viewpoint of the global ocean-land-atmosphere dynamical system, La-Nina is well entrenched. Tropical convective forcing has consolidated nicely ~0/130-140E extending from the East Indian Ocean into the SPCZ. WH (2004) MJO phase space plots show greater than 2 sigma projections in octant 5 without ENSO and approaching a nearly 3 standard deviation anomaly with it. However, this empirical technique reflects what I think is a resurgence of our quasi-stationary La-Nina base state. I do not think we have an eastward propagating signal like that observed during early-mid January. Phase 5 of the WH (2004) measure of the MJO OLRA snr composite plot nicely depicts the current situation of tropical rainfall.

The wind and convective signals are loosely getting back into sync, as are the tropics and extratropics. A “messy” Eastern Hemisphere subtropical transition to anomalous upper tropospheric East Indian Ocean (central Pacific) twin anticyclones (cyclones) continues. The latter is the zonally asymmetric component of tropical wind anomalies characteristic of a cold event.

However, similar to a year ago and not cleanly observed during this “encore”, there is now respectable interhemispheric meridional symmetry of zonally symmetric zonal mean zonal wind anomalies. These include ~5m/s 200mb zonal mean easterly wind flow anomalies throughout the Northern Hemisphere subtropical atmosphere, and easterly anomalies in excess of 10m/s ~75N (more said below). Reflective of a poleward shifted zonal mean polar jet; 200mb westerly wind flow anomalies of roughly 5m/s exist at 45N.

Also similar to the 2007-08 strong El-Viejo, the Northern Hemisphere midlatitude circulation is characterized by anomalous ridges suggesting a positive phase of a Branstator (2002) circumglobal teleconnection. Phase 3 of the GWO 250mb psi snr composite anomaly plot depicts this situation. Along with phase 4 for the MJO depicting tropical anomalies, a superposition of these composites is broadly representative of the global circulation. This response may continue for the next several weeks.

Updated through 3 February, global relative AAM is ~1.5-2 sigma below the R1 data climatology, an upward trend from its low of ~minus 2.5 sigma a couple of weeks ago (bear atmosphere rally?!). Including contributions from the surface torques, relative AAM tendency has increased to ~plus 15 Hadleys the last week or so. However, the WB (2009) measure of the GWO remains locked in octants 3-4 of phase space, strongly shifted toward the La-Nina attractor comparable to that observed during the 2007-08 boreal winter/spring. I do think a slow orbit is probable during the next few weeks, tilted toward La-Nina.

The record breaking (data going back to 1978) major sudden stratospheric warming (SSW) continues. See links in the Appendix for details. The zonal wave number 2 pattern of Northern Hemisphere higher latitude anomalous continental cyclones (~100E ad 100W) and ocean ridges bridging the pole has propagated down to at least 200mb. Surface weather across large portions of the Northern Hemisphere is already being impacted. A synoptic response has been for the European blocking (which played a role in the recent UK snowstorm) to retrograde into central Atlantic Ocean. The latter does not (yet) project strongly on the negative phase of the NAO, and serves as another example why it is important to understand the dynamics of teleconnections (the Rottweiler is always watching!).

In any case, arguably GWO processes starting December 2008 contributed to the SSW, and now the SSW is feeding back to the GWO. For instance, the polar latitude strongly anomalous upper tropospheric zonal mean easterly wind flow is helping to keep global AAM low, in a sense constructively interfering with La-Nina. Furthermore, AAM eddy transports from both the subtropics and high latitudes may be contributing to the anomalous westerly wind flow ~45N. Regardless of the details, working with what may be a maturing quasi-stationary La-Nina base state, tropospheric impacts from the SSW will continue for the next several weeks. Stratospheric time scales are very slow.

Regionally, the central Pacific Ocean ridge-expanding western USA states trough is probable to continue through the next 2-3 weeks. Blocking retrogression through Canada, perhaps bridging the Atlantic and Pacific Ocean ridges, is likely to keep an active storm track over much of the central and southern lower 48 states (in contrast to the poleward displaced zonal mean polar jet). There may be a period of anomalous cold and wet for much of the country, including an elevated risk of high impact weather (all types; should be understood), particularly ~week-2.

Somewhat typical of a La-Nina, much of the Arctic air (surface temperatures well under minus 50F across Siberia) is displaced toward Asia. However, some of this air will “bleed” back into the USA the next few weeks, ending the current respite from the cold winter for locations such as the Upper Mississippi Valley. Speculating farther, while March-June 2009 may have weather similarities to that period during 2008, the seasonal northward migration of the polar jet may be delayed. Including impacts from the severe tropical thunderstorm activity centered on Indonesia and northern Australia, I trust the expertise of the appropriate meteorological agencies to alert the public of additional weather hazards worldwide.


The formal announcement including an additional expanded outline for the 24 February 2009 one-day (~830am-530pm MST) workshop on the WB (2009) GWO has been released through various mailing lists, and is available on the ESRL/PSD GSDM web link. Let me know if you have not seen it. Please remember the intended audience of this workshop is forecasters who make daily subseasonal predictions. It will not be a “head banger’s academic ball”.

Links to CPC and PSD ENSO discussions:

The following are links to information about the stratosphere and other nice monitoring tools: (new stratosphere link!)

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)), is awaiting publication in MWR. A pdf of an in press version can be downloaded from the following link:

In addition to the subseasonal snr composite anomaly plots, we would like near real-time discussions with “weather maps” to 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, and unscientific!

Discussions will be very difficult to publish the next few weeks given shift work and preparations for the GWO workshop. I will attempt to post “something” ~13-15 February.

Ed Berry


snoman said...

Hi Ed,

Do you consider it likely the above normal heights over Greenland and northeast Canada, being progged by the models, will eventually retrograde back into Alaska? I feel that is the best chance the Pacific Northwest will have of seeing another Arctic outbreak this winter.

Thank you for your thoughts!


Ed Berry said...

Hello Jim,

What you suggest is a possibility during the next few weeks. At least much of the west coast will have opportunities for precipitation. The same is also true for the southern and central High Plains, where drought has been intensifying. For instance, here in DDC, so far, since 11/1/2008, we are in the top 10 driest (at least). Our records go back to the 1870s, including the Dust Bowl days.

Take care,

Harold Ambler said...

Hi Ed. I have read that the principal effect on weather from an SSW is a displacement of the polar jet. The explanation went that said displacement then led to cold weather in the American Northeast and other locations (among them Europe). That makes sense to me, and it looks like you take the same view.

On the other hand, and it's a big other hand, there has been a very impressive spike of lower troposphere temperatures in the last 5 weeks almost exactly contemporaneous with the SSW. Logic says that the tropospheric spike could not have been induced by the SSW, and yet they happen to be happening at the same time...

Have you reflected on this? Do you have any thoughts to share?

All the best, and thank you,

Harold Ambler said...

P.S. I should have indicated where I was getting my information from:

(Channels 5, 6, and 7). Roy Spencer indicates that the LT (bottom-most) channel has calibration issues at present, and suggests not to use it.

You can see glancing around the other lower troposphere channels (5-7) that serious warming appears to have begun about a month ago and doesn't show signs of letting up...

snoman said...

Hello again,

I have a few questions about the Earth AAM.

1. How is it calculated in comparison to the GLAAM?

2. How is it possible to have the GLAAM and Earth AAM both very low as they were in the 1950s and 1960s.

3. Do you foresee the Earth AAM data being released in numerical format anytime soon?

I am interested in this because this seems to be one piece of the puzzle that still hasn't come into line with how the atmosphere was behaving in the 1950s and 1960s which was a period of fabulous cold weather for the Pacific NW.

Thank you for any insights you can give on this!


Harold Ambler said...

You guys both probably know more about the Pacific Decadal Oscillation than I do, but I would look to it as the reason for the wonderful cold and snow in the 1950s and 1960s.

My reading indicates that when the PDO flips from positive (warm) to negative (cool), the effect on climate is cumulative. As the cool PDO began in the mid-1940s, it makes sense that by the 50s and 60s you had no shortage of snow out your way.

I would surmise, therefore, that similar conditions would begin there within 5 to 10 years. (Meanwhile, from what I hear, your December was more or less historically snow and cold already!)

I am someone who believes that most of the late 20th century warming was solar in origin and that the current solar minimum is likely to amplify the cooling associated with the negative PDO.

Ed Berry said...

Hello Harold and Jim,

I appreciate the time you folks take to read my posts and offer comments. There are a lot of issues that I certainly cannot address here. In fact, I wish you could find the time to attend our GWO workshop 2/24.

The first concern is the quality of data we have from the 50s and 60s. That is a matter I would want to look at very carefully. I think there is truth to the cold phases of the PDO per

and seems to match well the following from the 70s

In any case, I think there may be sample size issues using the PDO as a predictor, and I also think a good portion of the PDO is a response from the extratropical atmosphere. That is, not a source of boundary forcing. I come from the viewpoint of atmospheric dynamics meaning there are reasons for the red noise PDO variability.

For the SSW, cooling of the polar troposphere is completely consistent. Dynamically, one can argue anomalously high mslp suggests good radiational cooling over the deep snow cover. We have observing that response for the last 5-10 days.

For AAM, I would have to ask Klaus to make the text files available. However, I would also be concerned about the quality of data prior to R1. Negative earth AAM suggests anomalously low mslp. This is the mass term of the earth-atmosphere AAM budget. Having reasons, I think what you are seeing may be the result of a budget imbalance.

One issue Klaus and I have recently discussed is doing a careful AAM budget analysis comparing, for example, quasi-stationary states vs those with active subseasonal variability. Who knows when we will have time to this?

Best regards,

Ed Berry said...

Hello Harold, Jim, and others,

A correction to my last response. The reanalysis-1 (R1) data go back to January 1948. For some reason I was thinking 1968. In any case, the issues I discussed are still valid.

Thank you,