Cold Blast 4 Days Away…

December 2, 2009

A very cold looking map isn’t it?  00Z models have not backed off at all on the cold airmass coming down from Canada over the weekend and early next week.  The initial surge is a “normal” chilly airmass.  That comes in Friday night and Saturday morning.  Some of the models indicate a little bit of cloud cover and even mountain flurries, but that’s it.  No model shows any sort of significant onshore flow or cloud cover to generate snowfall over us the next 3 days.  By Saturday night a much colder upper-level trough comes down over us from the north.  The map here is for 4pm Sunday afternoon, click on it for a better view.  The upper trough is moving off to our south and at the surface modified arctic air will be pouring in behind it from the north.  So Sunday is the day the really cold air arrives.  I’m assuming models are slightly too cold, so we’ve stayed with high temps Sunday-Tuesday above freezing.  Read literally, the GFS would produce high temps those days closer to 30 degrees (on one side or another), but once again I’m assuming it’s a bit overdone.  I see the WRF-GFS has the airmass around 0 degrees Fahrenheit (-18deg C) by Monday morning at 5,000′ over the North Oregon Cascades…that’s really cold!  Last night and this morning’s ECMWF finally came into much closer agreement on the sequence of events over the weekend and early next week too, so that’s good news.

Seems like we’re aiming towards the middle of next week for a transition back into mild and wet westerly flow again.  It’s way too early to figure out exactly what’s going to happen.  Could be freezing rain or snow.  The GFS has gone several runs showing a quick punch of moisture up into our area on Wednesday.

Basically I feel more confident tonight that we are in for a good blast of cold air, definitely not historic though.  Maybe something similar to January 2007 when highs at PDX were only in the low-mid 30s before that “unscheduled” snowstorm arrived (I was in San Antonio…oops).  But I see nothing to produce snowfall until at least the middle of next week.  Okay, maybe flurries over the mountains Friday night, but that’s it.

Chief Meteorologist Mark Nelsen

Snow, Only on Blog Though

December 2, 2009

Richard Van Dijk sent me a note, he noticed that I can add falling snow to the weather blog for the Christmas season.  Thanks for that…and let me know if it really irritates you.

Speaking of irritation;  forecasts of snow in the next 5 days are a bit annoying.  We have not put it in our forecasts here because we can’t find a model that shows a decent setup for snow here…until later next week maybe?  I’ll have some thoughts later.