At the same time it is raining and in the upper 30s and lower 40s in much of the rest of the area. How can this be? The National Weather Service has been spotlighting this possibility for a while and the local high resolution models were going for this snow for days (see forecast from yesterday below-24h snowfall ending 4 PM) for forecast initialized 4 PM yesterday.
The key to this is southeasterly flow and the cooling influence of melting. A strong low is approaching the coast (see graphic) and that has forced strong southeasterly flow over
When strong flow approaches the Olympics it is forced to rise, producing enhanced precipitation rates. To see this, here is the latest Camano Island radar image (it can't see southern side of the Olympics well, but you get the idea). You can see the impact of the Olympics, with heavier precip on the eastern side of the barrier.
So southeasterly flow causes upslope on the mountains, which causes a heavier precipitation rate, which causes more melting and cooling, which results in the snow level coming down to the surface. This effect can also happen in other areas of enhanced precipitation, such as the Puget Sound convergence zone.
You pull the tail of a tiger and it is going to snap at you! On Tuesday, my blog noted that a ST writer was making fun of forecasters for changing their predictions in time. And on Wednesday, I complained about the big headline of MEGASTORM in the ST that day, when the latest forecasts were only for 3-6 inches over Seattle.
Well, the ST began with reporter Nick Provenza in an article "Forecasts Change, Right? Professor Mass" in which he pointed at my earlier speculation that a heavy snow was possible (my forecast subsequently changed with new model output). Sort of like suggesting that I was the meteorological version of Newt Gingrich, calling for moral purity while he was playing around with multiple women. But I only gave one forecast at a time! Monographical prediction.
And today they brought out the heavy artillery: ST humorist Ron Judd, who suggested an "about-face forecasting retreat on Tuesday." As if holding to a failing forecast is the route to victory!
Now a bit of good-natured ribbing is fine, but this correspondence shows that many, including some ST folks, don't appreciate the essential nature of forecasting, and particularly that forecasts change in time, and generally improve as you get closer. My profession needs to find a way to communicate the evolving forecast without losing the confidence of the media and the public. Polls change in time and people don't seem to get upset and make fun of pollsters. We need the same for meteorologists!
By the way, there is a pretty good story today in the ST on the ice-storm forecast by reporters who took the time to understand the problem.
Finally, a fun parody of the local snowstorm coverage is now available:
http://www.youtube.com/watch?v=hHqcf0jcPRk
