Spring Showers?

March 2, 2009

003 I've been real busy today with a midday school visit in SW Portland and then a 2 hour visit to a PCC Meteorology class this evening.  Lots of fun talking to the adults about the pros/cons of the business.  Today definitely felt like the start of the "springtime" convective season.  As I came out of the first school around 1pm, a very nice CB had developed over the middle of the area with a dark base and hail/big rain drops…big stuff for March 2nd in Portland.  Just a sign of things to come in April and May, hopefully.

Of course we really just care about the cold upper-level troughs forecast to drop down over us (or just to the east) later Thursday-Friday and again on Sunday.  There was a dramatic difference between the 12z ECMWF and 12z GFS.  GFS was cold and showery with a good chance for snow to low elevations both periods.  ECMWF pushed the trough much farther east with mild springlike weather.  Drew and I (we collaborate on the forecast) went for a middle of the road approach.  That leaves snowflakes out of the 7 Day forecast, but chilly weather from Thursday forward through early next week.  The 00z GFS seems to have confirmed that now; a slight shift eastward with the Thursday trough and slightly warmer 850mb temps.  I see it barely touches -7, about the time preciptation ends.  So I'm glad we made that move.   Sunday is still in play, but I wouldn't be surprised if/when the GFS backs off on cold air.

I could really use a nice big ridge with a few 70 degree days, but that's probably a bit much to ask in early March, especially in a La Nina year.  One thing is still certain about the 7-10 day outlook;  it's going to remain drier than average in this first half of March.  A ridge well offshore with troughs dropping south along the coastline is not a very wet pattern…just some light rain at times…Mark Nelsen