Friday, January 28, 2011
The Real Deal about La Nina and The Upcoming Weather
There has been a lot of bad information distributed by some media outlets about La Nina and this winter (e.g., "Where is La Nina", "No Show La Nina", "Winter is Over") and some talk about snow on Sunday over the lowlands. I would like to deal with this by going into more depth about what La Nina does to our weather. I will also vent about the media.
Well, I hate to complain, but I was entirely misquoted on the front page of the Seattle Times today. They claim I said:
"Meanwhile, University of Washington meteorologist Cliff Mass says his projections show there’s little chance the Puget Sound area will see another big snowstorm or flooding this season"
This is NOT what I told them and is not what is stated in the interior article.
What I DID say is that it is rare to get MAJOR windstorms and flooding events in our region after the third week of February. That the really big snowstorms and cold waves tended to be before then and that we can get moderate snow events (several inches to say a half-foot) into the first week in March. After the first week in March, it is exceedingly rare to get more than an inch or two over the lowlands.
This is a La Nina year and our chances of getting snow during the next month--in the lowlands or in the mountains--- is ENHANCED compared to normal. But there are no guarantees. La Nina is like weighting the dice ...you increase the odds of a certain throw, but there are other possibilities.
I deal with the media quite a bit and I have to admit some frustration about how often bad information gets in print or on-air. I ask myself, if the information about something I know about is in error quite frequently, can I believe what I don't know about? Reporters have less and less time to do their stories and editors jump for a dramatic, but perhaps inaccurate headline. Even leading newspapers like the NY Times are doing some bad things (like hyping the connection between Siberian snow and east coast cold waves) or reporting...and providing headlines...for unrefereed junk science (like the suggestion that China dust was causing intensified Pacific storms). Just frustrating. We need more science reporters with the time to get the story right.
Current computer runs for the next several days show NO major snowstorms, windstorms, floods are anything else that would send KING TV's Jim Forman rushing out to get his famous parka (which I expect will be in the Smithsonian one day). But we will get colder for a few days, Fraser River outflow will hit Bellingham and NW Washington, winds will accelerate in the Columbia Gorge, and there could be an highly isolated snowshower on Sunday. And we will see a complete dry out starting Sunday that will last a long time.
So lets state some facts. We are in a moderate La Nina year and will be for the remainder of the winter. La Nina years are frequently associated over the NW with above average precipitation for the fall and winter, colder than normal temps after January 1, and greater than normal snowpack and lowland snow after New Years. La Nina years usually have higher than normal pressure and upper level ridging over the eastern Pacific, with enhanced northwesterly flow coming into our region.
None of this is guaranteed...just a higher probability that we will see it during a La Nina year.
Well....have we seen signs of La Nina? You bet we have. Time and time again ridging in the eastern Pacific has developed, as has NW flow over us. I could show you plenty of historical examples this winter, but how about 4 PM this afternoon?
Or 4 PM on Monday?
Here is a plot of the difference in sea level pressure between La Nina years and all years (the anomalies from climatology in weather talk). Note the positive anomalies in the eastern Pacific (red and yellow), and the negative anomalies (blue) just inland
And here is this year from Nov 1- Jan 26th. You can see the La Nina influence--with the positive anomalies (higher pressure than normal) south of the Aleutians. Similar to the typical La Nina year, but with small differences that have lessened the chances for snow (like weak troughing--lower pressure than normal--off our coast).
And has precipitation been above normal this winter so far, as it should for a well-behaved La Nina? Yes, it has. Here is the proof for Sea-Tac over the past 12-weeks (red is observed).
So those claiming that La Nina has been a no show are not quite right. But what about the snow??
First, the winter is NOT over yet and we could still make up the mountain snowpack and get ahead of normal. Would not surprise me in the least. And to get lowland snow around here is REALLY tricky--you need the hard to secure combination of cold and wet. Consider this weekend....we will be close in some respects. Colder air is coming up, particularly late Sunday and into Monday. But the precipitation will be over then. No cigar. Yes, there could be a few snow showers as the last precipitation leaves, but this should not get any mayor gassing up the salt trucks.
Posted by Cliff Mass at 8:38 PM