Tuesday, January 31, 2012

Wayward La Nina


This has been a La Nina winter, but you might not know it.  In fact, the La Nina has been intensifying as indicated by the cooling waters of the tropical Pacific, as shown by the plot of the sea surface temperatures Nina 3.4 area of the tropical Pacific seen below.  The figure actually snows SST anomalies...differences from normal...which are now more than 1C cooler than normal.

La Ninas are usually associated with wetter than normal fall and winter over the Northwest, but so far we have been a bit drier than normal (see plot for Seattle):
And snowfall in the mountains, which should be above normal, particularly after January 1, is near normal over Washington and about 60-70% of normal over Oregon, even after all the snow of late January.   The latest forecasts for the next week suggests a VERY dry situation after we get past the rain tonight and tomorrow AM.  The National Weather Service long range forecasts for the entire winter have been for typical La Nina conditions:  wetter and colder than normal, but except for two weeks in late January, this has not materialized.

So what is going on?  The answer is that the typical La Nina circulation has not set up consistently so far this winter.   Why is that?  I can't tell you and I am not sure anyone can.
Typically, La Ninas are associated with major ridging (high pressure) over the Aleutians and troughing (low pressure) over the Northwest.  This brings cool northwesterly flow towards our area and troughing is associated with precipitation:  thus,cold and wet.  Here is a figure showing the typical configuration aloft for La Nina (500 hPa, around 18,000 ft).  This figure actually gives you the difference from climatology.  The classic La Nina pattern is evident.

But this year the pattern has been different.  Yes, the ridge is there, but it has moved much farther east, leaving us in a much drier position.  Only for a few weeks in January has a La Nina pattern been observed.   This figure illustrates the evolution of the upper level pattern for the last two months to show you what I mean (colors give the anomalies from climatology).


Now here is the interesting part.  The next week should be dominated by a huge ridge over the West coast and we have some confidence in this because nearly all the forecasts, ensembles and others, and showing it.  Just to give you a taste from the UW modeling system from Thursday to Sunday.   And the ridging continues in the following week (although I don't know if I can believe it that far out).



Seattle winter really ends in the beginning of March...greatly reduced chances of major windstorms, floods, snowstorms.  So we are running out of time for major lowland action.

And did I say what the models are suggesting for next winter?  No more La Nina and a move to neutral conditions.  Although infrequent, the biggest and baddest storms occur in neutral years.  Something to look forward to.

14 comments:

raja said...

I know there is no way to tell for certain, but had the ridging been "as expected", would we have been SLAMMED with all of the stuff that has been hitting Alaska (although moderated by local conditions)....?

richard583 said...

Interesting. — My own general impression and theory broader ENSO related, is that from this point forward, through until a peak centered generally between 2015 and 2017, things will move toward steadily more warm, annually, where considering the fuller span of the main equatorial Pacific, both sea-surface and above it. This, with both main higher latitudes greater regions, North and South, looked at more over-all, cooling correspondingly. — With this idea considered along with that that next year things will be shifting toward more neutral, both greater stores of cold north, together with a greater potential for basic moisture generation / production south - resulting, would certainly tend to lend to the idea of more intense storms.

ILoveWinter! said...

Sure hoping this nuetral time period will bring us a real upcoming summer, fall, winter, and spring. Especially a real fall and winter! I love stormy weather but have been so dissapointed with the last few winters around here! (and springs, and summers, and falls!)

Ben F said...

As a geologist, I can't imagine looking forward to the next big earthquake or landslide. Even though it's interesting to study, seems a bit short-sighted considering all the negative effects to property and personal safety.

I love the blog, just never quite understand the "looking forward to storms" mentality

wanne1 said...

I'm glad there will be a few dry days to deal with all the branches that came down during the ice storm. Any update on Leah?

blackcap said...

Well, I can't call this winter as a bust, myself, because most of us in western Washington did get a pretty good couple of lowland snow events (and an ice storm) out of this winter. And if you lived in Olympia or Chehalis, it was more than "pretty good": "epic" is more like it for those locations.

For Portland and southward, however, it's definitely been a complete dud of a La NiƱa. Most of the time it was snowing or icing here, it was raining and in the 50s in the Willamette Valley. The whining from extreme weather fans on Mark Nelson's blog is getting deafening.

Seeingred said...

And the same was predicted last year, La Nina transitioning to a neutral year. I think I'll wait until Nov/Dec for that prediction.

Lance said...

I'm just hoping that this La Nina doesn't give us a repeat of last spring, that was dreadful.

Unknown said...

I wouldn't count on any prediction for ENSO conditions for next winter. Historically, accurate predictions do not happen until after the "Spring barrier". In fact, last year at this time, MANY of the models were calling for an El Nino event. Obviously wrong.

Klaus Wolter, who knows more about these events then anyone, points out that there have been 10 times in recorded history (since 1900) where there were two straight Nina winters. What happened the following winters? 4 times there was a 3rd Nina, 6 times there was a Nino, and there has yet to be a neutral year after two straight Nina's.
http://www.esrl.noaa.gov/psd/enso/mei/mei.html

Buddy said...

Deja vu, CPC does it again (although not as extreme). It amazes me having 98 percent confidence that the first 14 days of Feb. will be completely dry and warm, yet they still put EC for the month.

I'm actually ok with that. But on Dec 1st, they didn't remove the above precip and below temps under the exact same scenerio for that month.

Hindu said...

Great post. There are factors missing, which I'm sure is always the case with weather. The easy stamp would be global warming.

TreeTimer said...

On a different topic but a current one, the freezing weather storm in Europe was named/sponsored by the Mini Cooper mfr. The BBC article said the university that names these "vortices" is the only one outside the US to do so. Where in the US is this done? This is not just assigning a first name to a hurricane. This is a monetary sponsorship that helps fund a university in Germany. Is it also a university in the US? or a commercial venture?

jamiem said...

Cliff Mass will you talk about sunshine? Do weather models suggest we will get any amount of warm sunny days this summer? Last summer seemed so mild, cold even, and not very sunny. Thanks, ps we love your blog !

Linda Khandro said...

Cliff...I wonder if there is a typo in this phrase from the beginning of your post? "With an upper level ridge overhead and the associated high pressure to the west of us..." Should that be "to the east of us"?

Love the blog, thanks so much!