Friday, January 30, 2009

Update: La-Nina + Major SSW = Where the Atmosphere has Never Gone Before?

“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.

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

This will again be short! Please see links below for SSTs. Local and relatively shallow warming of equatorial Pacific Ocean SSTs has occurred west of South America, similar to a year ago. Anomalies are ~plus 1-2C. Tropical-extratropical interactions linked to the recent strong MJO and seasonal issues may be contributing. Our respectable downwelling oceanic Kelvin wave ~150m depth has propagated to about 150W. Any future impacts from the latter are unclear. Stay tuned. The warmest SSTs globally persist across the southwest Pacific, with totals ~30C in the region of New Guinea. (note the initial projection) (link 18)

La-Nina is reloading. Tropical convective forcing has returned to the Eastern Hemisphere with some consolidation ~0/120E while a somewhat separate region persists across the warm southwest Pacific Ocean. The MJO signal has weakened. There is little projection in WH (2004) phase space removing interannual component, but ~1.5 sigma in octant 3 (through 28 January) retaining it, reflecting the resurgence of La-Nina. Monitoring will tell if another eastward propagating signal of tropical forcing evolves. Other options include two areas such as a quasi-stationary Indonesian region concurrently with episodic southwest and west central Pacific strong to severe tropical convection.

Global relative AAM is approaching negative anomaly magnitudes comparable to the 2007-08 strong La-Nina. Updated through 26 January, AAM was ~2.5 sigma below the R1 data climatology forcing the WB (2009) measure of the GWO deeply (~2 sigma) into octants 2-3 of phase space. Zonal mean easterly wind flow anomalies have become quite strong throughout the equatorial and subtropical atmospheres, ~5-10m/s at 200mb, and up to 15m /s across Northern Hemisphere polar latitudes. The latter is a response to a sudden stratospheric warming (SSW; more said below). A loose superposition of phase 3 for both the 250mb snr psi composite anomaly plots of the MJO and GWO generally represent the global circulation, and that should continue for at least the next 2-3 weeks. This means our familiar pattern of anomalous midlatitude ridges including the central Pacific Ocean favoring a trough in the region of western North America.

Forced by (unpredictable) dynamical processes responsible for the strong west coast ridge a couple of weeks ago (see 23 January posting), a major SSW is in progress. In fact, data records going back to 1978 (see new stratosphere monitoring link in the Appendix) suggest this SSW is the strongest given this time of year. A well pronounced zonal wave number two circulation structure in the stratosphere is present, with lobes of the polar vortex across the Arctic latitudes of North America and Asia. Interacting with the La-Nina base state, the troposphere is already being impacted, and that will continue for at least the next several weeks. Large anomalies of zonal mean easterly wind flow is propagating downward into the upper troposphere of the Northern Hemisphere high latitudes as I type.

Synoptically, a possible regional-scale response is for tropospheric blocking initially across Scandinavia to retrograde through the North Atlantic and Canada then into the North Pacific Ocean during the next few weeks. The NCEP GEFS and other ensembles are starting to capture this scenario. That suggests the storm track should shift south across the lower 48 states of the USA later week-2 and perhaps continue most of February. Additional feedbacks (not discussed) from the South Pacific Ocean tropical forcing may also contribute to bringing the storm track farther south. Areas that have been anomalously dry this winter may get much needed precipitation. In fact, there may be some weather similarities to February 2008 across the USA next month. I trust the expertise of the appropriate meteorological agencies to alert the public of additional weather hazards worldwide.


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. An extended outline was sent today, 30 January, which should also be avialable from 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)), has been accepted for publication MWR. A pdf of the in press version can be downloaded from thefollowing 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! I plan on posting at least an abbreviated discussion on ~7 February 2009.

Ed Berry


Brett said...


Here in southern Oregon and northern California (MFR CWA) we've been trapped under ridging for most of our Wet Season. Seems the expected normal to wetter climo effects of La Nina have focussed farther north so far, though we have retained what snow we've gotten alright due to cold and dry (low dewpoints). We've been thinking the retrogression of the ridge would bring a parade of storms, but now it seems cut-offs and southern CA storms are more likely for much of Feb, week 2 to later. Feb 2008 was very dry for us (~25% of normal in MFR). Since the wetter La Nina conditions have focused farther north, do you think this more southern storm track might also be shifted north? Wishful thinking on my part, and I know it's all complicated, since we're going where we may have "never gone before" since at least 1978... Any thoughts would be helpful, as the CA drought seems to be creeping northward... Thanks. Brett

Ed Berry said...

Hi Brett,

I would like to think the Pacific Northwest will have some precipitation opportunities during February. You are correct that CA will get initial impacts (they also need precipitation, as you know). However, the central North Pacific Ocean ridging (with variations) should favor your area, at times. The Devil is in the details and we need to monitor.


JordanWeather Forecasters Team said...

Hi Ed,

I am Mohammed Al-Shaker, a private Weather Forecaster in Jordan, Middle East.

I just want to inform you, that we are having the most dry pattern (in winter season) ever on record!! And we finished January without any significant rainfall, while our rainfall average in Amman (Jordan's Capital) in January is about 60mm, we are having a serious drought threatening.

The main reason, is that western Europe and NW Africa are under very stormy pattern, and this allow for a ridge forming exaclty above Middle East, same as the Ridge over Western USA, and the mean reason behind all that is "Inactive Atlantic".

My questions, do you see any change in the pattern in February? Such as establishing a high pressure to the east of the Atlantic or Western Europe, Since we are having a major SSW?

I hope to hear from you,
Thanks Very Much for your amazing analysis and posts,

JordanWeather Forecasters Team said...
This comment has been removed by the author.
Ed Berry said...

Hi Mohammed,

Thank you for the post! I am flattered to be getting a comment all the way from the Middle East.

I wish I could be more optimistic about precipitation chances since this is your wet season. The SSW is actually favoring the regions you mentioned for precipitation.

As the higher latitude ridge retrogrades across the Atlantic into Canada, that may allow a full latitude trough across much of western and central Europe. This may be too far west for you. However, the South Pacific Ocean remains active and westerly wind flow is being added to the subtropics from it. That may allow some systems to impact the Middle East ~later week-2 and/or week-3.

Please stay in touch!

JordanWeather Forecasters Team said...

Hi Ed,

Thanks very much for your reply.

I just want to make sure of your point, that SSW calls for wet spell over central and western Europe, and also in north-west Africa?

I am noticing that the NWP models, especially the ECMWF are stregnthening the upper-level lows during the second week of February, and this strenght not for Europe, its arround the NH, so is this because of the SSW??

My last question, can you help me with any analogs for the coming month you suggest? even if your post title is indicating that there no analogs!

I want to inform you, that Persian Gulf is receiving very heavy rain amounts, since there is a strong ridge over Jordan and Eastern Europe, sending for them unusual storms and rain. Snow fell in UAE for the second time since 2004, and it was the heaviest on record. In general, they are experiencing very rare conditions for this year sometime with arctic (Siberian) blasts, and other with wet upper-level lows systems.
I will keep you in touch,

Ed Berry said...

Hello Mohammed,

That is simply amazing weather!
Since I focus on the dynamics of weather-climate linkage within our GSDM framework, I have not directly looked at any possible signals involving the stratosphere. In fact, as you point out, the sample size is limited.

In general, observationally, SSWs suggest an increased probability of polar latitude tropospheric blocking leading to regional southward shifted storm tracks including the possibility of anomalously intense lows. For the current situation, the retrogression I offered leading to western and central European troughs appears likely. Whether or not the latter is a consistent response particularly with La-Nina is unclear.

Eastward progression of closed lows toward the Middle East later week-2 and perhaps week-3 may be reasonable given the Southwest Pacific Ocean forcing (for instance). Some models are trying to suggest that (ex., ECMWF).


JordanWeather Forecasters Team said...

Thanks Ed,

I will keep you in touch next week with latest observations and forecasts.

Greg said...

Hello Ed,

I am loving these updates.

From what I have gathered the unexpected SSW's will cause the -NAO over the next 10 days. Combined with a -PNA and a possible -EPO with a split flow (Euro + GFS 8-10 day) there is a good shot for an overrunning event across the eastern CONUS.

Also, if the easterly winds at 200mb across the northern Hemisphere persist, would the high latitude blocking across the Northern Atlantic and Eastern Canada persist as well?

If they were to diminish in intensity would that cause the tropopheric blocking to weaken?

Ed Berry said...

Hello Greg,

I think there will influences on the troposphere from the SSW for the next several weeks. These will generally "dribble" downward, given the slow time scales in the stratosphere. That suggests anomalous polar latitude easterly wind flow and blocking structures. Weakening of the easterlies may weaken any blocking patterns.

Given the current upper tropospheric/stratospheric wavenumber 2 pattern, loosely there should be ridges across the oceans and troughs over land. While there does appear to be a retrogressive transient, anticyclonic wind anomalies may persist from the North Pacific through Canada into the North Atlantic Ocean. Again, these influences are in the presence of other processes tied to La-Nina/GWO and tropical forcing.


Greg said...

Thank you for your response Ed.

Captain Climate said...

Wow!!! We live in interesting climatic times.

Ed, "Thank you" is not a strong enough expression to quantify the gratitude I have for how you share your passion for understanding the big picture of the climate.

The SSW has me very excited because of how long and strong it is. It has also been difficult to find a precedent for it.

Do you think that last year's eruption of Kasatochi (Alaska) is playing a role in enhancing high latitude blocking opportunities?

I also have begun to wonder if there are 2 types of La Nina's. One driven by tropical oceanic influences ("bottom-up") leading to the stereotypical result of US west coast troughs and east coast ridges. The 2nd type being driven "top-down", a version that would be a side effect of atmospheric circulation (AAM).

What do you think?


Ed Berry said...

Hi Dean,

Thank you for the comment and support! There are no good responses to the questions you ask. I had not heard there was a volcanic eruption in AK last year. I have read that there may be one currently on the verge.

In any case, eruptions have to be quite large to impact the global weather. The SSW started nearly a month ago from upward energy propagation from the troposphere responsible for the PNA ridge.

The ENSO "cycle" is a global coupled evolution involving the ocean, land and atmosphere. Everyone of these is different, and given our sample size, the unknowns far exceed what we think is understood. That is one reason why people run many models with lots of assumptions to gain some understanding.

Take care,

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