Wednesday Evening Update: Snow into edge of metro area

8:45pm Wednesday…

Today turned out pretty much as expected, with a few last minute twists & turns.

1. We saw a rain/snow mix which changed to mainly rain as the cold front moved through during the evening commute
2. Clark county warmed up to around 40 as our “mesoscale” models showed; no snow for most of you up there.
3. No measurable snow for almost all of us.

What was different than expected?

1. Cold Gorge wind was very persistent (surprise!).  Although quite a bit more reasonable compared to a few hours ago, it is still transporting cold continental air westward into the eastern edges of the metro area.  Temperatures are hovering just above freezing in a narrow area along the Columbia River east of I-205
2. Due to that, plus the cooling air overhead, snow has been falling for several hours in the western Gorge, all the way into Camas and Washougal.  Just got a report that two inches have fallen in Bridal Veil, that’s where we should have only seen freezing rain.

Take a look at current temps, only the numbers below 34 degrees plotted below. (click for a better view)

Areas to the right of the yellow line are generally seeing snow.  Mainly or all rain to the left.  Yet in general the snow level west of the Cascades is around 1,500 to 2,000′ right now.  Then how is it snowing down to the Columbia River in Clark and Multnomah counties?  What would typically be about a 1,500′ snow level right near the Gorge and into Camas/Washougal has become “sea level snow” since the last 1,000′ or so are near/below freezing due to that east wind; snowflakes are coming down much lower than one would expect in this pattern.   Due to this, and more precipitation on the way, the NWS has upgraded the western & central Columbia River Gorge to a Winter Storm Warning.  3-6″ likely in these areas.  The pressure difference through the Gorge does continue to weaken and it’s possible at some point Camas/Washougal/Troutdale lose the easterly wind.  If so temps will rise a few degrees.  They sure won’t go down any lower through tomorrow morning.

Through the rest of tonight we’ll see waves of showers moving onshore behind this evening’s cold front.  In general the snow level will remain above 1,000′ through tomorrow morning.  But anyone at/above that elevation in the metro area could see a skiff of snow on the lawn/barkdust/car.  Same setup again tomorrow night and Friday morning.  Beyond that time we’re headed back to a milder weather pattern for the last 1/3 of January.

Chief Meteorologist Mark Nelsen

First Snow & Rain Moving Through At Midday

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:

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.

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.

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

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

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.