Cold & Snow Update: Sunday Morning

December 1, 2013

It’s time to prepare (if you haven’t already) for our coldest weather in 3-4 years; only about 2 days away now.  But if you want snow, that’s likely not going to happen at the lowest elevations.  At least in the next few days.

Highlights

  • Very mild with light rain at times today.  South wind gusts 30-40 mph possible through this evening.  Rain will be heaviest from 5-10pm.
  • Ski areas have been washed out by rain, 2-3″ overnight!  Meadows and Timberline are just operating a beginner lift each…it’s pouring up there!
  • Light showers Monday…all rain, since sticking snow stays well above 1,500.
  • Showers end soon after sunset Monday.  Snow level at that point may be as low as 1,000-1,500′.  Those areas could get a dusting.
  • Dry from that point all the way until at least Friday.  This means no snow in the lowest elevations from Longview to Eugene is a very good bet.
  • Colder east wind arrives Tuesday morning as cold arctic air pours into the Pacific Northwest.
  • Coldest days Wednesday-Friday with highs near or slightly above freezing for the western lowlands of Oregon and Washington.  We haven’t seen that since a few days in November 2010 and during a cold spell in December 2009.  When the wind drops later in the week, we’ll see low temps well down into the teens, maybe even an 8, 9, or 10 in the coldest spots.  Our 7 Day forecast summarizes high temps and lows (in the city) well.
  • There are hints of some moisture returning this Friday or Saturday, if so, it would be cold enough for snow…all is not lost yet if you want some white stuff!

This graphic summarizes the snow (or no snow) situation well:

snow

Details for the hardcore weather fans…

I was in Reno from Wednesday afternoon until late last night.  It’s interesting to come back and compare what I wrote 4.5 days ago with the maps right now.  Actually they aren’t much different!  I always see comments complaining about how the models are always flip-flopping and the GFS is horrible (partly true), but the big picture hasn’t changed at all.  A wet and warm system just ahead of a cold upper-level trough for Sunday, then cool showers Monday, then dry northerly flow Tuesday and beyond.  Sure, we’ve seen swings between just a “regular” cold spell and a huge arctic blast, but for the average Mr. Public,  they would barely notice the difference between a high of 25 and 35.  I did check in on models and maps off/on the past few days, and I did notice the ensembles of the models have often been colder than the operational runs.  I wonder if they have been misleading a bit?  Possibly, and I don’t know why.  But last night’s 00z ECMWF and this morning’s 12z GFS ensembles are a bit closer to the operation runs; by Wednesday afternoon only one or two ensemble members from each model shows anything colder than a -10 degrees at 850mb.  Finally a little better agreement:

tseries_850t_000-360_Portland tseries_850t_000-384_Portland

They predict a nice blast of cold and dry air, but not a huge event like 1998, or 1989, or 1990.  That said, it WILL be our first real hard freeze since Thanksgiving 2010.  That one lasted only 2 days or so.  So I’d say this will be more like December 2009.  The cold/dry air begins moving in Monday night and by daybreak Tuesday we’ll see dewpoints falling dramatically and a breezy east wind.  Right now the east wind doesn’t look too wild through mid-late week.  But I sure wouldn’t want to go up there to “experience the wind” now.  You thought a 45 degree wind was cold?  Try 25-30!

Now let’s talk snow.  There is an unfortunate disconnect between the onshore-flow showers Monday and the colder air coming down from the north.  A classic case of the moisture and cold air not lining up properly here in the lowlands of Western Oregon/Washington.  Snow levels through 4pm tomorrow are at best flirting with 1,500′.  Then soon after that time the dry northerly flow takes over.  If temps are still well up in the 30s to around 40 in the lowest elevations, that doesn’t do us much good.  Far more likely are wet areas freezing up tomorrow evening and lots of icy spots for the Tuesday morning commute.  I live at 1,000′ and think it’ll be real tough to get anything other than a dusting here.  You can see the WRF-GFS from the UW doesn’t even have hints of hilltop snow that we sometimes see in marginal situations:

or_snow48.48.0000

But at least 6-10″ in the Cascades to push the sputtering ski season along.  This should be enough to get Meadows and Timberline to open another lift or two; although today’s rain sure isn’t helpful!

Too bad, it would be nice to get something out of this cold air.  There have been hints of a shortwave dropping down in the northerly flow and possibly spinning up some moisture for snow later this week.  This was the 00z ECMWF, showing some snow for Friday night & Saturday morning (the snowflake on our 7 Day forecast):

ecmwf_apcp_f156_nw

The 12z ECMWF is coming out right now and it shows (I waited 15 minutes for it to arrive in this spot)….well, well, well, still a little system for later Friday.  A colder shot of air behind it this weekend too!  Note the digging upper level heights coming down the Canadian coast:

500vty_f132_bg_NA

Then the surface map showing precipitation spreading over Western Oregon and the cold offshore flow…that’s a great setup for snow.

ecmwf_apcp_f132_nw

Then an even colder airmass right behind it on Saturday…brrr!

ecmwf_apcp_f144_nw

Great…now that I’m back I’ll be model riding too.

Enjoy the warm rain today, and get those hose bibs covered!

Chief Meteorologist Mark Nelsen