Cold Front Signals Big Weather Change

November 11, 2011

A nice cold front has been moving through the Metro area the past hour.  We often don’t see a signficant change as a cold front passes here in the Pacific Northwest.  The “weather waters are muddied” a bit due to the modifying effects of the mild Pacific Ocean.  But this time around we’ve seen a sharp shift in wind from south to northwest (gust to 33 mph at PDX) along with a sharp jump in pressure.  That’s a satisfying conclusion to a day that started with sun (or fog, depending on where you were), and gradually clouded up.  Speaking of a pressure rise, a 6 millibar westerly gradient has suddenly developed through the Gorge…expect strong wind there in the next couple hours! 

Looking ahead, another system moves inland tomorrow afternoon, then another on Monday afternoon & evening.  Both of these will be juicy systems with plenty of mountain snow.

Things get far more interesting the 2nd half of next week.  Both the GFS and ECMWF are in general agreement on a pattern similar to what you see in the graphic above.  Very chilly air sweeping south out of Alaska, over the Pacific, and right in over us.  This is a good setup for heavy Cascade snow and snow to quite low elevations.  Since this is still 6-8 days away, details are lacking and change with each model and model run.

For example, the 12z ECMWF has thicknesses down to around 522dm from Thursday morning onward, cold enough with onshore flow to bring sticking snow down to at least 1,000′.  Then it shows cold easterly flow and a low pressure system approaching from the southwest on Sunday; possibly a setup for a brief snow or ice event, especially in the Gorge.  The 12z/18z  GFS was similar with snow in the hills Thursday and beyond.  It also showed some sort of clash between cold easterly flow and Pacific moisture around a week from Monday…only 10 days away!  Lots of fun to speculate, but for now the only thing I’m confident about is the snow levels down to at least 1,500′ late next week.  We’ll see how the rest pans out.   I guess I can also confidently say I’m done with my outdoor chores for the season.  I’ve built the shell of a greenhouse (for the next La Nina spring?) and just have to put in the windows when I get a break in the weather…maybe in February?

Stay warm and dry this weekend!

Chief Meteorologist Mark Nelsen