Inversimageddon Almost Finished; Freezing Rain On The Way

January 21, 2013

I know, it’s not a real word, but the past 7-10 days have been quite interesting considering we’ve been near/under a dry upper level ridge!  50s, 60s, and even some 70s in the higher elevations and 30s down below; a very strong inversion.   You folks in the central and southern Willamette Valley have been stuck in the muck (fog and cold air) for about 10 days!  Check out Salem’s numbers:

MarkTemperature_SalemColdTemps

Andrew from Silverton noted earlier that if Salem stays below freezing again tomorrow, it’ll be tied with 1979 for 6 days at/below 32.  And the most 32 or lower days since that time; yet no record low temps.  It has just been consistently cold, but not “arctic cold”.  We’ve definitely had much colder weather in the past 30 years, but it lasts just a few days each time.

Absolutely nothing changes in our weather through Tuesday night, so another day of sun here in the metro area and fog/clouds in the Valley.  But, there is relief in sight…a weather system gives us a mild southerly wind along with some rain very late Tuesday night and the first part of Wednesday.  That means Wednesday afternoon we’ll see the usual showers and sunbreaks…get the sunglasses ready Salem, it might be blinding!

The transition from the current cold weather at the lower elevations to mild temps and moisture is an issue though.  As I said, nothing will change through late tomorrow night.  So temps will drop off into the 20′s to around freezing everywhere between the Cascades and the Coast Range below 1,500′.  Above that level up to around 3,000′ temps remain above freezing through Wednesday afternoon.  Uh-oh, I smell freezing rain coming on…

This is what I’m showing at 10pm tonight, it covers the highlights:

MarkFreezingRain_Metro

  • Why freezing rain and not snow?  Much too warm above for snowflakes to survive; we are in a very shallow layer of cold air here at the surface except in the Columbia River Gorge.
  • How long will it last?  Not long, all models show a pretty decent southerly breeze blowing up the valley well before noon; with such a warm airmass overhead it shouldn’t take much to wipe out the thin layer of cold below.
  • How much does it take to make roads icy?  Very quickly…can be 5 minutes.  Freezing rain is liquid rain that freezes on contact, so it happens really fast.  I spent 1976-1982 living in the Mt. Angel area and saw freezing rain just once.  It started sprinkling in the morning at my bus stop and 5 minutes later the bus was starting to slide on the road.  What a downer that we made it to school and they didn’t cancel!  The point is that unlike snow, freezing rain can change road conditions very quickly.
  • Will it affect the Wednesday PM Commute?  No, 40s by midday all areas west of the Cascades and probably even the far western Gorge too.  This isnt’ one of those situations where the cold air takes forever to leave, a south wind should move it out quickly as mentioned above.

What about the Columbia River Gorge?  In one way the forecast is easier here; it’s plenty cold for freezing rain from Troutdale eastward.  In fact east of I-205 is the one part of the metro area where I think freezing rain is just about guaranteed for the Wednesday AM commute, even if the rest of the metro area somehow escapes it.  It is a little tougher with respect ot precipitation type.  I think freezing rain is “a lock” from Troutdale to Bonneville Dam, and it may just be freezing rain all the way to Hood River too.  There is small chance it starts as snow from Cascade Locks to Hood River; tough call.  I’ll have a better idea Tuesday.  There isn’t much moisture at the eastern end of the Gorge so there might not be much of anything east of Hood River.

Enjoy one last real sunny day in the Portland area tomorrow before more typical weather comes back.

By the way, I borrowed the Inversimageddon word from a poster on the Western Wx Forum.  I hope you don’t mind!

Chief Meteorlogist Mark Nelsen


For the Geeks

January 21, 2013

Monday 4pm…

Last night’s monthly ECMWF run maps; Week 2 through Week 4.  That takes us through the 1st half of February:

500za_week2_bg_NA

500za_week3_bg_NA

500za_week4_bg_NA

And the 12z ECMWF 850mb ensemble chart:

tseries_850t_000-360_Portland

Chief Meteorologist Mark Nelsen


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