Back to Work: Wind & Snow

December 12, 2006

I still feel a bit under the weather today, but after looking at the weather maps I just couldn’t stay away!  Plus Andy is sick too so that leaves no one to cover me tonight.  What a team player eh?

First for tonight…nice pacific system moving onshore.  Looks like a good slug of heavy rain briefly overnight then back to shower tomorrow.  Deep low moving towards Queen Charlotte Islands.   A windy/rainy night but nothing too unusual for mid December.  By the way, don’t forget that today is the anniversary of the Dec. 12, 1995 windstorm.

Speaking of windstorms, all of our eyes are obviously scanning every single possible map/model for clues as to who is going to get hammered.  Of course as I write this there is no 00z model guidance available yet so I’ll post again later with my thoughts on 00z info.  It is pretty clear that a low is going to develop explosively and land probably on the NW Washington coast…they sure like to go up there don’t they?   You may recall that after November’s storms I decided the NAM-WRF is no longer my friend, so I’m leaning heavily on the GFS this time (that includes the UW-MM5 GFS).  As some of you have discussed at great length below…by the way, are you all employed?…there is a heck of a gradient to the south of the low as it moves onshore.  My 37 year old eyes could barely see the isobar packing between Portland & Eugene.  But I get 20-22 millibars from EUG-OLM!  The old rule of 3.15 x EUG/OLM gradient = 60-70 mph gusts in the metro area.  If so it’ll be a big windstorm from Eugene to Kelso.  But of course only a slight deviation in track to the north or a weaker cyclone could just give us the usual 45-50 mph.  Timing isn’t much of a debate…looks to be between 7pm-midnight Thursday evening.  I am impressived by the insistence through several runs of the GFS that there will be an "elongated" low with the big isobar packing over us.  It’ll be real interesting to see if it really sets up that way.

Now behind that storm a much colder airmass comes in.  Looks like a 1,500′ snow level at the lowest during the daytime Friday since it’s such strong onshore flow.  Remember that this is immediately following the gusty southwest wind and it’ll still be windy/breezy the rest of the day Friday.  I doubt we can get snow down to or below 1000′ in that pattern.  Then a quick shutoff of showers overnight Friday night and into Saturday morning when it’s finally cold enough for everyone to see snow.  With weak ridging then until sometime early Monday (via the ECMWF & 18z GFS), I just see a partly cloudy and chilly weekend.  Next system arrives from the northwest on Monday and pulls up southerly breezes again.  I see that as very similar to the late November one where the cold air was gone in a snap since the low is going by to the north.  For these reasons I’m downplaying the snow threat quite a bit.  Too warm Friday, too dry Saturday/Sunday, too warm Monday w/ precip…I’ll update later when 00z models arrive…Mark

11PM UPDATE: 00z models not too much different, landfall near the NW tip of Washington Thursday evening.  Notable again is the tight packing of isobars between 7-midnight over our region.  Hmm, could be a GREAT windstorm, but we’ll see.  It’ll be fast, over by early morning.