Saturday, November 21, 2009

An Intense Low and SNOW!!!

November 21, 2009
1:38 P.M.

Look at the graphic above. It shows the track of the vigorous low I was talking about in earlier posts. This low looks like it will not bring high winds to our area, but the coast and southwest interior could get slammed.

Usually we don't see winds as strong as forecasted (gusts to 70 miles per hour) with lows this deep (this low is only 990 millibars). Winds, however, are not determined by the absolute barometric minimum of the low. Rather, they are determined by the gradient of low pressure. This is a small-scale, surface low pressure system that will still be in the development phase when it comes ashore. All these factors combine to make a very steep pressure gradient. I would not be surprised in the slightest to see a gust to 90 miles per hour in one particular spot - Naselle Ridge in the SW coastal mountains. This place commonly receives high winds, and a similar (albeit much stronger) event on November 3, 1958 gave it a 161 mile per hour gust. Go to for more information on this storm. The Seattle area should not see strong winds from this storm.
Another aspect of this storm is that it will bring tons of snow to the mountains! Take a look at the 4km mm5-gfs mesoscale model. Amounts of 30-40 inches are seen throughout the Olympics and amounts of 2-3 feet are seen in the Cascades, with even even higher amounts at higher elevations like Mt. Baker and Mt. Rainier.
Even Seattle will see a fair amount of rain from from this storm. From 4 P.M. Saturday to 4 P.M. Sunday, I'd expect an inch of rain here in Seattle, and the rain will be heavy at times tonight. The coast will see higher amounts, with local amounts up to 4 inches possible.
After this, we will get into a MUCH more benign weather pattern with only a few weak systems approaching the NW. One will clip the area Monday and showers will persist through Thursday. After that, Thanksgiving weekend looks completely dry! I'm not too happy about that but I bet a lot of other people are. After getting all the new snow we should pick up in the next day and the additional stuff during mid-week, the weekend should make for some fantastic skiing in the mountains. I'm definitely going to try to check that out. :)

Have a good weekend,


  1. Wind advisory posted for the puget sound region! It would sure be nice to end this crazy weather with a high wind warning, maybe we will get lucky? Next week sure looks boring, there is pretty much nothing of interest in the models.

  2. yeah i agree
    i have to say i wasn't expecting a wind advisory.
    This is a time when a coastal radar would really help... a slight difference in track of the low could bring high winds here. I guess we will find out soon :)