Last night there was a burst of light snow, accompanied by strong winds, in the Bellingham, Whatcom County, San Juan Island areas...and some snow reached Port Angeles. The explanation is simple: moisture from a small low circulation rotated into the opposing cold flow of the Fraser and other gaps in the Cascades. Here are some snowfall measurements provided by the National Weather Service:
WHATCOM COUNTY SNOWFALL (INCHES)
BELLINGHAM 1.5(MILES)SW 3.0
BELLINGHAM 2.4 SW 2.3
FERNDALE 2.1 NW 1.5
BELLINGHAM 9.8 NE 1.4
SAN JUAN COUNTY SNOWFALL
WALDRON 1.1 NNE 2.6
LOPEZ ISLAND 3.9 NNE 2.0
ORCAS 0.7 NNW 1.0
FRIDAY HARBOR 6.2 WNW 1.0
PORT ANGELES 8.1 SSW 2.2
PORT ANGELES 2.5 SSW 0.9
Today there was a dramatic transition in much of the lowlands of western Washington as cool, dry northerly flow pushed south. The air above the Puget Sound lowlands is now cold enough for snow. Alas, cold is not enough...we need moisture...and it looks like that will not be forthcoming.
I waited to write this blog until I saw this night's runs, and to look at the probabilistic predictions from National Weather Service and the UW ensembles, as well as the European Center Global Model (the gold standard).
My conclusion, if the models are correct, the central Puget Sound region, including Seattle, will get little or any snow. But we will get extraordinary cold--particularly on Tuesday morning. On the other hand, Portland and Willamette Valley, will see the white stuff.
Here are some graphics regarding the current situation. First the precipitation probabilities from probcast...which uses an ensemble (a collection) of forecasts and then applies sophisticated statistical post-processing. High probabilities of precip (snow) in the Cascades, southern WA, and Oregon. Not much over Seattle and north.
And here is the snow forecast from the high-resolution WRF model for the 24h ending 4 PM Sunday. The Cascades and SW Washington get some light snow.
And here is for the next 24h. Forget most of western Washington for snow.
The models would really have to be in error for Seattle and the northern lowlands to get significant snow..which has happened. And there is still some uncertainty to the solution. But lets be honest, snow lovers will probably be highly disappointed. The cold is serious business though...anytime it gets below 20F around here, there is trouble. I expect large areas of the lowlands away from the water to get below 25F and a number of colder spots in the teens.
There is one group, of course, that likes supercold weather...plumbers. Freezing pipes are good for business. A few years ago, weather.com (the weather channel) was going for a crazy cold wave....a plumber called me up all excited...should he bring on more people to handle all the business? You can lessen their income by making sure your outside faucet don't freeze up and that you insure that pipes in crawl spaces are insulated or heated.
Finally, I should make things clear...making a good forecast is more than looking at a few model simulation plots. To do it right, takes not only a physical understanding of the situations that have produced snow, but judgment about which models are doing well, have done well in similar situations, the consistency in time of each model and between models, and today a careful study of the new technology of ensemble predictions. A good forecast takes quite a while to do.