Snow Tonight? No, Unlikely In Lowlands

February 23, 2018

10am Friday

Last night was COLD!  Lots of mid/upper teens in the coldest part of the metro area.  I had a 15 at my house which was the coldest of the winter.  But it’s late February and daytime temps rise quickly.  Most of us are around 32-35 degrees at 11am.  We’re headed for high temps around 40 by 4pm.

There is talk of another snow evening this evening and overnight in the lowest elevations.  But as mentioned in my previous post, IT’S A NON-EVENT THIS EVENING AND TONIGHT

KEY POINTS

  1. THE THREAT FOR SNOW STICKING ON ROADS HAS PASSED FOR THIS EVENT, THROUGH AT LEAST SUNDAY EVENING
  2. Temperatures will likely stay ABOVE FREEZING from now through Sunday evening for almost all the metro area and lowland locations
  3. Light snow showers or rain/snow mix WILL develop this evening for most of us, then quickly change to rain showers between 7-10pm below 1,500′
  4. Near/above 1,000′ there could be a brief accumulation on non-road surfaces in the metro area between 4-7pm, that’s a big IF moisture arrives as anything other than light flurries.  Best spot for an inch or so (before warming in the late evening) might be north Clark county & Columbia county hills well above 500′.
  5. By 10pm, snow will only be sticking near/above 2,000′.  Late tonight the snow level drops back down to around 1,500′ after a cold front passes, but that’s it.

 

TO SUMMARIZE  You can go about your normal lives now through the weekend; it’s unlikely weather would affect your plans…except for rain of course

 


Why don’t I think we’ll see sticking snow this evening?  It’s because this IS the setup that DOESN’T give us snow.  This isn’t a “BC Slider”.  It’s a weather system sliding by to the north with a cold front passing through in the middle of the night.

NO COLD EAST WIND OUT OF THE GORGE

We don’t have any supply of cold & dry air to keep things cool like with our typical snowstorms.  In fact it’ll be a breezy west wind by morning out there.

WARMING ATMOSPHERE OVERHEAD WITH SOUTHERLY FLOW

Check out the WRF-GFS at 4pm.  That’s cold enough to bring snow (at least in the air) down to sea level

The temperature contour is up around 2,500′.  Note the 2-3 millibars southerly flow from Eugene to Portland.   Then 10pm…

Wow, that is a classic southerly warm-up signature.  Above freezing west of the Cascades up to over the 2,000′ elevation!  About 6 millibars surface pressure gradient from Eugene to Olympia.  This will give us a south wind in the valley/metro area 10-20 mph with gusts to 30!  It doesn’t snow here in that setup.  I’ve also checked cross-sections and soundings from models.  All show the same thing.  I will be home here this evening at 1,000′ in the Cascade Foothills.  I’d be surprised if I get more than a dusting even up here.

NO MODEL GIVES US SNOW

Here’s the WRF and ECMWF…not even a hint of sticking snow at lowest elevations

 

I didn’t mention surface temperatures, which will be well above freezing through the evening for all lowland locations.  We should top out around 38-40 this evening, then temperatures hold steady in the mid-upper 30s through the night.  We may actually pop up to 40 or beyond after 10pm.

I’ll be off until Sunday, time for a weekend!

Chief Meteorologist Mark Nelsen