no snow for you today

11am Wednesday…

So far things are going about as planned weatherwise.  Temps dropped to below freezing for most of us last night.  As of 11am all parts of the Willamette Valley up into Kelso/Longview are above freezing, a gusty east (cold) wind is blowing out of the Gorge, and a bit of “downsloping” southeasterly wind has arrived in the Cascade foothills, central Willamette Valley, and Clark county.

Now the first band of snow and rain is passing overhead.  I’ve seen reports of snow in St. Johns, McMinnville, but just rain in central Portland.  A mix in Beaverton too.  Looks like McMinnville was able to get a dusting as that passed overhead:

mcminnville

WHAT’S HAPPENING AS OF MIDDAY?

At 4am the balloon sounding over Salem said “all snow”; the air was below freezing all the way up through the atmosphere.  But that has changed; there is a huge storm that has developed off the coastline.

satellite

We are on the east side of that storm, which means strong south and southeast wind developing in the lowest few thousand feet of the atmosphere.  The air just above the surface up to around 3,000′ is warming quickly.  That continues until a cold front passes overhead around sunset (the sharp back edge to the cloud cover).  So for the next couple of hours it’ll be a rain/snow mix until temps get a bit warmer overhead.  As you can see the temperatures down here at ground level are too warm to allow snow to stick and we’ll remain above freezing through tonight.

web_metrotemps (1)

All the mesoscale models (with better terrain and resolution) say no sticking snow in metro area tonight, including Clark county.   The WRF-GFS model was perfect showing temperatures rising up to around 40 or higher in a weird sort of southeasterly “downslope” wind flow up there.  Here’s the snow forecast through 4am

wrf_snow4am

and the NAM-NEST model is similar, this is ending at 1am

namnest_1amsnow

The mixed precipitation should change to all rain as the main cold front band passes overhead 3-7pm.  After that it’s frequent showers tonight.

SUMMARY FOR LOWLANDS WEST OF THE CASCADES

  • Mixed rain/snow continues at times through early afternoon, changing to mainly rain.  Although a mix likely continues up in northern Clark County and maybe Columbia County around Scappoose and St. Helens.
  • Mainly rain showers tonight, although mixing with snow on hills.
  • Could see a trace to 1″ eastern metro hills up around 1,000′ and above.  1-3″ above 1,000′ possible any of the Cascade foothills (east of Battle Ground, Camas, Sandy, Silverton etc…)
  • Freezing is unlikely in metro area tonight.  But just like the last few nights, there could be spots where breaks in clouds allow some local freezing.  If it happens most likely it’ll be west metro areas.
  • Scattered light showers Thursday, still mixing with snow at/above 1,000′

COLUMBIA RIVER GORGE

A bit more complicated here because a shallow layer of cold air isn’t going anywhere.  This isn’t quite the typical situation since the real cold air is only about 2,000′ thick.  But since it’s not a real warm atmosphere overhead there should be no problem keeping precipitation type as snow from Bonneville Dam eastward.  There’s a very narrow area at the west end of Gorge that will see freezing rain late this afternoon/evening.  That’s from near Corbett/Cape Horn east to about Multnomah Falls.  Then back to a snow/rain mix later tonight in those areas.  So east of Multnomah Falls or Bonneville, expect a Trace to 4″ in the Gorge.  The trace would be out near The Dalles…just not that much precip to work with.

 Chief Meteorologist Mark Nelsen

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