Tuesday, December 23, 2008
Stunning Pic and Snow
Last night didn't get quite as cold as expected because of the development of low clouds during the evening...but still cold enough to turn everything to ice and keep it that way. There is a stunning picture this morning, which I have attached. This is a high-resolution visible image from the NWS geostationary weather satellite at 35,000 km above the surface. According to aircraft reports this cloud has a base around 5000 ft and a top at 7000 ft. You can see the major mountains sticking throught it...like Rainier, Adams, and Baker....and this are clear shadows from the mountains on the cloud below. Would be wonderful to fly out and see this....assuming the plane was able to take off!
Other than roadway ice...not much happening today. The computer models are consistent on the approach of a Pacific system (see satellite picture)...which should bring snow to our region after midnight. There should be an inch or two by the end of the Wed. morning commute.
At this point it looks like temperatures will warm up enough by midday that that the snow might turn very wet or even to rain at the lowest elevations...but we are right on the edge. And then later in the day another system moves in--a stronger one associated with a Pacific occluded front. Now this storm will have lots of precipitation and if it were snow...then we would have a very major event. Right now, the models are suggesting the most of the precipitation from it will be rain at low elevations (below 500 ft)...but just barely. If the models are off or some of the model physics is error (like its tendency to mix out cold air too quickly) then we could have a major event. So right now...best estimate at lower elevations is snow starting midnight to 4 AM and continuing until midmorning...leaving a few inches. Then warming a bit and a let up in the precip, with the change to wet snow or rain miday. Then later in the afternoon the precip will pick up and probably turn to rain at low elevations and wet snow above roughly 500ft. But there is uncertainty in this. And knowing about uncertainty is in itself valuable information. Meteorologists like myself sometimes are very sure about the forecast, and other times we know there is substantial uncertainty...or a wide range of possible outcomes. A major challenge is learning how to quantify this uncertainty and then communicate to users like yourself....we have a major project to do this at the UW...including meteorologists, statisticians, psychologists, and others. The grant challenge in weather for the next ten years or so.
Getting back to the forecast.... on Thursday...another system... a tight, low pressure center moves southeastward....but the latest runs are suggesting that it will go far enough south to spare the Puget Sound region. Portand will not be so lucky. Will have to watch it. And on the weekend a warmer, wetter system is on tap.
Posted by Cliff Mass at 9:01 AM