Updated Forecast

Friday, December 11, 2009

1:09 A.M. (yes, you heard that right. I took a huge nap this afternoon so I’m wide awake now)
The models are still in very, very little consensus on what is going to happen. Scott Sistek of Komo4 said he wished that there was a question mark icon for the forecast because if there was he would put it up there in a heartbeat. I’m not exaggerating. Meteorologists around the city have little to no clue as to what to expect. Models are completely all over the map, and even the same models have wildly different runs by the quarter day.
Let’s take a review of what happened today (or technically yesterday). Yesterday started off very, VERY cold because of excellent radiational cooling in the atmosphere. Light winds, low humidity, and clear skies allowed the low in Seattle to reach a bone-chilling 16 degrees. That is very cold, colder than any time last year (even though last year had more snow). There is a little pond up by my house that I have been able to walk on because it has been so cold! However, I only walk on it with supervision and very carefully and because the pond is only about 3 feet deep at its deepest. I do not encourage walking on ponds unless you are sure of the thickness of the ice. It should be at least 4 inches before you walk on it. The ice on the pond by my house is around 2 inches or less but I can still walk on it, probably because it is very strong ice (it is completely clear, which I’m assuming means it is strong). The high got above freezing today as temperatures warmed 2-6 degrees from yesterday as some warmer air drifted into the region, but tomorrow will be perhaps a little cooler simply because some clouds will prevent the sun from heating anything up too much.
Another thing of interest, which Cliff Mass mentioned on his blog this afternoon and I saw this morning as my dad drove me to school, was the steam rising off the lake. The lake is around 50 degrees and the air was around 20 in most places by sunrise, so the relatively warm, moist air rising off the lake was visible as it condensed in the very cold temperatures. There was also very little wind so it was very visible. I really don’t like to steal and I hope Professor Mass does not consider this plaigarism, as I did get this picture from his blog, but this is what I saw this morning and I was absolutely amazed. Check out his blog at cliffmass.blogspot.com for more (and better) weather forecasts and a note about the steam fog.
Anyways, models are showing a decent shot of snow to the south of us Friday night through Saturday as a low pressure system spins some moisture up north, but it probably won’t quite reach us. At the same time, a weak disturbance will drop out of the north, bringing snow to perhaps as far south as Everett, but probably not all the way to Seattle. We will have to see though – Seattle may very well not be in the gap between storms, and we could see a couple flurries here and there, but I’m not expecting any accumulations over a 1/2 inch.

The bigger chances for snow are Sunday and late Monday night, and these events are the ones the models are having so much trouble with. The one on Sunday doesn’t look to cause much in the way of snow right now, as it is pegged a little further east than optimal and is relatively dry. The NAM, another American model, gives it more juice, which could give us a more widespread snow, but that doesn’t look likely. The GFS puts a convergence zone in north Seattle, which could drop some snow there while leaving the Seattle proper area dry, or the zone could be a little further north or south than forecasted. Anyways, you get the point – difficult forecast. But as you can see, even the drier mm5-gfs does show some snow over the region.

The next shot (Monday night) also gives us a chance for snow. The moisture will be there, but will the temperatures be cold enough? The Euro says no. The GFS used to call for a major snow event (see previous post). The GFS now calls for snow north, perhaps spreading southward. Your guess is as good as mine, but I’d go with the Euro in this situation, as it has been the most consistent. But I’d happily be proven wrong. The above graphic is what the GFS is predicting – see the snow north of Seattle but rain southward.

In any event, we will see heavy rain next week and get back to rainy weather. Remember what that stuff is like?

Stay warm!
Charlie
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