A Winter Wonderland New Year’s Morning? Mainly In The Hills

December 31, 2016

11am Saturday…

As mentioned in the previous posting, a very weak weather system moves over the Pacific Northwest tonight and New Year’s morning.  During much of the system’s passage, temperatures will be too warm at the lowest elevations for snow to stick.  But near the end, as showers are tapering off, snow may stick in spots all the way down to the valley floor.

METRO AREA HIGHLIGHTS

  • Your New Year’s Eve plans are safe  There won’t be any snow on roads in the lowlands through at least 2-3am.
  • But any of us could see snow mixed in with the rain during the overnight hours.
  • Near/above 1,000′ (top of the West Hills), some accumulation is possible, but even then it may be a degree or two too warm for sticking snow.
  • 4am-10am a dusting to 1/2″ is possible anywhere, but I’d lean towards a dusting and not that half inch.  Many of us get nothing tomorrow morning.
  • The rest of tomorrow we’ll be above freezing, at least through 3pm, so I think roads will be clear.
  • An arctic front passes through the area tomorrow evening; that means a sudden arrival of cold east wind and all wet areas will freeze.  At that time we’ll be dry, or just a few flurries maybe.

CASCADE FOOTHILLS AND COAST RANGE

  • Rain or rain/snow showers change to mainly snow showers above 500′ by midnight.  At that time some roads will start getting snow-covered above 1,000′.
  • Anytime after midnight and through Sunday any road in the Coast Range and above 500-1,000′ west slopes of the Cascades could get snow-covered.  That includes Sandy, Estacada, Beavercreek, Mill City etc…
  • Expect 1-3″ in these areas, more above 1,500′.

 

The NWS is going for a Portland snowstorm tonight and Sunday morning, but I think it’s unlikely.  They are forecasting 1-3″ in the metro area (3″ on hills) and have a winter weather advisory up starting at 10pm.

I feel that’s way overdone for several reasons.  The biggest is that we’re in mild onshore flow through around sunrise Sunday.  In fact southwest wind picks up this evening and continues until almost day break.  Freezing levels are above 1,000′ through 7am tomorrow, when almost all of the moisture will be falling out of the sky.  I’ve seen this many times here in Portland.  We’ll be too warm down at the valley floor until sometime after 4am to even think about snow sticking down here.  There is excellent model agreement on this as well.  That southwesterly breeze is a real killer (for snow) UNLESS the atmosphere is colder than what we’re expecting now.   Take a look at model snow forecasts from the ECMWF, WRF-GFS, & RPM and they agree.  Note the RPM snow is mainly after 4am:

rpm_4amsnow1km ecmwf_snow_18z rpm_snow_12z-1

 

None of those inspire a lot of confidence for a sledding day Sunday in Portland do they?

Now during the day on Sunday cooler air gradually filters in from the north, but we’ll be battling daytime heating (a little) too.  Leftover snow showers could dump a dusting anywhere during the day, but most areas will be slightly too warm still for stickage.  So we should stay above freezing through 3pm, then we plunge into a frozen abyss.  Okay, that’s a bit dramatic, but I don’t know when we’ll go above freezing again…maybe about 6 days from now?  We’ll see about that.

To wrap it up, I think many of us will wake up to a white dusting, but a frozen city with snow all over the roads like we had with the big fiasco in mid-December is unlikely.

Happy New Year!

Chief Meteorologist Mark Nelsen