Friday, January 23, 2009

Reloading La-Nina, but with a SSW twist???

“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.

http://www.cdc.noaa.gov/map/clim/gsdm.composites.shtml

Many map room plots are missing due to on-going upgrades. These issues are being worked on.

This will be short! Some warming of SSTs has occurred across the far west central equatorial Pacific Ocean (totals ~30C) as well as the west of South America. The latter may be a similar occurrence to a year ago. Overall, global SSTs remain “steady state” including ~minus 1C anomalies (warmed slightly) across all Nino regions.

http://www.wmo.int/pages/prog/wcp/wcasp/enso_update_latest.html

http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html

http://www.pmel.noaa.gov/tao/jsdisplay/

http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18)

http://www.cdc.noaa.gov/map/images/sst/sst.long.time.gif

The global ocean-land-atmosphere dynamical system is recovering from the recent strong perturbation on La-Nina. Importantly, linked to MJO convection across the South Pacific Ocean at the time, there was large amplitude meridionally directed Rossby wave energy dispersion (RWD) across the North Pacific Ocean (with Southern Hemisphere symmetry). The RWD forced the westward shifted PNA ridge that was responsible for the severe cold outbreak centered on the Upper Mississippi Valley last week. Several diagnostics (including EP fluxes) indicate that tropospheric wave energy from this RWD has propagated into the stratosphere and a sudden stratospheric warming (SSW) may have been initiated. More said below.

The MJO signal is centered on Africa, and interactions with extratropical wave energy propagations are intensifying deep convection across the equatorial Indian Ocean. Zonal mean easterly wind flow anomalies (~5m/s at 200mb) have returned to the tropical and subtropical atmospheres. Updated through 21 January, global relative AAM is already ~2sigma below the R1 data climatology, the lowest since early October 2008. I do expect a further decline (like our recent financial markets!).

Summing up, a coupled GWO/MJO evolution from octants 7-8 the last week or so into at least 3-4 in phase space is likely the few weeks, constructively interfering with La-Nina. The global circulation shown by ~phase 3 of the 250mb snr psi composite anomaly plots for the GWO and MJO appears probable by week-2. This means our familiar pattern of anomalous midlatitude ridges, including the central Pacific Ocean ridge and a downstream trough in the region of western North America.

Regionally, the on-going discontinuous PNA retrogression is similar to that observed early December 2008. This is being forced by the current weakened La-Nina base state including residual Indonesian tropical forcing. As La-Nina reloads the next few weeks, troughing is likely to return to the Gulf of Alaska then extend into western North America. In contrast to the high confidence outlooks for the USA issued November 2008 for December, it is unclear how far southeast these next series of troughs may extend into the western USA. Should the storm track remain anomalously shifted poleward, dryness may intensify over portions of (for example) the central and southern Plains. Typical of a La-Nina base state, the Northern Hemisphere polar vortex retracted during late December, and that has been the case until very recently.

However, unusual for La-Nina, and essentially not observed during the 2007-08 cold event, a serious monitoring issue the next 30-40 days will be if a possible SSW disrupts the polar vortex. Depending on timing of behaviors, including the possibility of another MJO coming out from the Indian Ocean into the west Pacific ~weeks 3-5, there may be significant weather impacts on the USA which are currently unclear. Stay tuned. I trust the expertise of the appropriate meteorological agencies to alert the public of additional weather hazards worldwide.

Appendix

The formal announcement for the 24 February 2009 one-day (~9am-5pm MST) workshop on the WB (2009) GWO has been released through various mailing lists, and is available on the ESRL/PSD GSDM web link (cited above). 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:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

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

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

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

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html

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

http://www.wmo.ch/pages/mediacentre/news/index_en.html

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 thefollowing link:

http://www.cdc.noaa.gov/map/clim/wb08_revised_final.pdf

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! I plan on posting at least an abbreviated discussion on ~30 January 2009.

Ed Berry

12 comments:

steve said...

Hi Ed
Very interesting post, as usual.
Even many uncertainties are probable next weeks, I try to ask you some questions about weather ramifications.
Do you think troposphere will "react" on the probable SSW? I mean: do you think there will be sufficient coupling to bring the antizonal signal from stratosphere to the middle latitudes troposphere next week?
And if so, which kind of weather regime do you think will be the dominant one in euro-atlantic region, given the La-Nina reload and the probable coupled GWO/MJO evolution into 3-4 in phase space next weeks?

I speculate on a North Atlantic blocking and a –NAO (or even a Scandinavian blocking) which can give a harsh weather period in Western Europe, but numerical models, as far as they are concerned, seem to persist in forecasting a zonal weather regime.

Thank you.

roqs2stoned said...

I'm still trying to get a handle on this whole global ENSO signal... I'm watching the SST's and they are being affected by the warm SST's off S America in the east and the Kelvin wave in the west. This is where the ENSO action is... is there something in your atmospheric scheme that is affecting the variation in the behavior of the ocean in the west and the movement of warm sst's in the east?

Ed Berry said...

Hello Steve,

Thank you for the comment. The possibility of stratospheric warming feeding back into the troposphere during the next several weeks exists. However, the details are unclear.

Generally SSWs can lead to tropospheric blocking at the higher latitudes and equatorward cold air discharge. If we should lock into GWO/MJO phases 3-4, that may suggest a deep trough and cold pattern for the western half of the USA. Should tropical forcing come out "just in time" with the higher latitude blocking, anomalous cold may favor eastern North America. A -NAO may also be more probable at that time suggesting cold/wet for Europe. However, -NAO can occur even with an amplified La-Nina base state due to (GWO) red noise processes, such as observed at times during 2007-08.

The models continue to play catch-up, as is typical during GWO/MJO 8-1-2 transitions in phase space. Overall, the circulation will be interesting to monitor the next several weeks, and predictability will be quite challenging.

Ed

Ed Berry said...

Hi rogs2stoned,

The GWO is closely linked to ENSO variability. The SST behaviors you mentioned have been slowly evolving for weeks responding to circulation variations including those I have discussed (weakened trades/actual westerlies leading to a downwelling oceanic Kw, etc.)

ENSO variability is a global phenomena. All tropical ocean basins can contribute to a circulation response having anomalously low or high AAM characteristics.

Ed

packattack said...

Hi Ed,

In the last couple of blogs you were saying that you expect to see similar temperatures and precipitation numbers to that of December 2008 to begin after the 20th of January and last well into February. Has this timetable been pushed back some? It's already the 24th and we still haven't seen any rain in southern California now for a full month and the models aren't showing any rain anytime soon either. In fact, they are showing ridging, not troughing, for all of next week and into early February. December precipitation anomalies were significantly above normal for southern California. Do you expect this cold and wet December-like pattern to return before the start of February? I sure hope that this pattern lasts through most of the following month because we badly need it.

Thanks for your time.

Ed Berry said...

Hi packattack,

While currently not the "greatest" precipitation event for CA, you may be missing much of it where you are at. The reports I have seen would suggest that. You can thank the past strong MJO, fighting La-Nina, for what precipitation has fallen.

The retrogression has occurred. However, it is a transient response to the past "weak residual of La-Nina", and the "main event" is yet to come. These evolutions are similar to December 2008, as is the current weather across much of the country. Obviously, the unpredictable details will never be the same.

What has changed is the increased uncertainty particularly for sensitive locations like yours. The La-Nina base state is rapidly re-intensifying as I type. For example, global rel AAM is ~2sigma below the R1 climo. That is the lowest yet for this "encore".

Bottom line, models have been struggling badly (typical of 8-1-2 transitions). However, numerous ensembles after ~day 10 are starting to show the situation I discussed (GWO phases 3-4, typical of a cold event). Regardless, the Pacific Northwest is much more likely to get anomalous heavy precip than S. CA. This is not good for you. However, stay tuned. The WPAC is warming and we may see another decent MJO come out (for instance; not the only "player") later in February.

Ed

packattack said...

Ed,

Thanks for the insight and timely response. I appreciate the time you put into the blog. You are correct about us missing most of the rain. Although models were showing a wide range of 1-1.5 inch amounts for the storm that just came for all of southern California, we ended up with less than .1 inches in almost all of southern California with favored locations getting up to a quarter of an inch. I think it has been ridiculous how poorly models have been all winter for west coast storms. I do see that the ridge is shifted west, but the problem I am seeing is that there is no trough digging far enough west to bring any rain here this coming week. Just a few days ago, every single model had a huge trough and low pressure system spinning off of the California coast bringing in huge amounts of rain/snow, just like the December storm that hit. Then they fluctuated back and forth between stronger and weaker storms all week and now they just show a weak inside slider type system with almost no precipitation. NWS was releasing forecasts and statements saying we were going to see 2+ inches of rain from this coming Sunday through next Wednesday. This is the 3rd or 4th time this year that NWS was confidently predicting a huge storm for us within a day of it hitting and then they start to slowly back off before we get virtually no precipitation whatsoever. I apologize for the frustration, but its hard to understand how every storm that is forecast to hit this area ends up either underperforming terribly or not happening at all. This type of pattern has been going on now for the better part of 5 years and has even happened during an El Nino year. I've been waiting patiently for over a month for a chance for storms again and when we finally got one, it ended up being no storm at all so I guess I'll now have to wait another 10 days before we get a "chance" of a storm again.

I have seen the GFS ensembles showing GOA low pressure and west coast troughing extending all the way down into my area by around day 10 for the last week or so, but these same ensembles have been drastically wrong on their forecasts for as little as 1 day out. It also seems that the return to a west coast trough keeps being delayed in the ensembles, staying right around day 10 for the past week. As you said "the main event" is yet to come, so I'll keep my hopes high that a favorable pattern will develop in early February. Once again, thank you for your time and insight.

Take care!

snoman said...

Hi Ed,

Would you say it's true any MJO waves in February are more likely to be in phases 3 through 5 as opposed to the recent unlikely venture into 7 and 8? I am still trying to figure out how an MJO was able to amplify to that degree in phase 8 with cold ENSO and significant negative GLAAM. Also, do you think the current very low AAM assures this La Nina will survive for a while?

All in all this winter seems to be an enigma wrapped in a riddle. I feel like a great winter is being stolen from us in the West.

Congratulations on the apparent increased interest in your blog! I am an admin on a weather forum where your insights are brought up quite often.

Jim

Ed Berry said...

Hi Jim,

Thank you for the comment about the interest in our weather-climate work. The recent strong MJO surprised all of us. We can go back and offer scientifically defensible attribution including the role of the GWO (the MJO is part of it). However, there was little predictability (dealing with red noise). As I discussed in past posts, I think the seasonal/annual cycle working with anomalously warm southwest Pacific SSTs at the time contributed. The former tends to be amplified during La-Nina.

Tropical forcing is increasing across the IO while Indo and the SW PAC are still active. It is probable convection will consolidate ~IO/Indo (~80-120E) during the next 1-2 weeks, while the SW PAC stays a "wild card". We will need to monitor for another coherent MJO coming out.

The global circulation, in terms of AAM, is the most in the depths of La-Nina for 2008-09. Regardless of details, the La-Nina character of circulation,etc., are not going to go away "anytime soon". I think a mature response across the PNA sector should evolve during week-2 and continue into week-3 meaning a GOA trough expanding into the western USA states.

Regards,
Ed

roqs2stoned said...

Ed, In the west, there is a small amount of change in sst's and upper ocean heat, it looks due to the kelvin wave. I gotcha on how the atmosphere is contributing to that situation. But it looks like the main area of sst warming in the last 2 weeks is that area in nino 1 + 2 and 3. A couple of weeks ago you and I had a short discussion on how the warmer sst's off the southern South American coast would affect the nino regions. That looks like it is due to the high pressure cell that tends to hang around 100w and 35s and the surface winds that are associated with it, pushing surface water north into the nino regions. My question is, where did those warm sst's originate... ACC? SW Pacific?... and how did the atmosphere affect the movement of these warm sst's according to your scheme?

Ed Berry said...

Hi rogs2stoned,

The recent warming of SSTs in the Nino 1+2 regions has similarities to what was observed about a year ago. The anomalies are shallow, and there may be a seasonal contribution.

The strong MJO that propagated through the WH about a couple of weeks did contribute to the excitation of surface westerly wind anomalies in that region. Like you point out, the extratropics also had a role. These westerlies/weakened trades may have induced some downwelling. It will be interesting to monitor any role that our propagating oceanic Kelvin wave from the west may have during the next several weeks.

Ed

Ed Berry said...

Hi rogs2stoned,

The recent warming of SSTs in the Nino 1+2 regions has similarities to what was observed about a year ago. The anomalies are shallow, and there may be a seasonal contribution.

The strong MJO that propagated through the WH about a couple of weeks did contribute to the excitation of surface westerly wind anomalies in that region. Like you point out, the extratropics also had a role. These westerlies/weakened trades may have induced some downwelling. It will be interesting to monitor any role that our propagating oceanic Kelvin wave from the west may have during the next several weeks.

Ed