Winter Storm Warnings Issued

December 7, 2016

4pm…

I haven’t changed my thinking for this evening, but made the TV graphics to support the forecast from the previous post.  Midday models looked the same:

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Tomorrow’s Snow & Ice: Looking Better! Not as Snowy/Icy

December 7, 2016

11am Wednesday…

I’ve taken a look at all the overnight/morning maps and models.  Several things stick out:

  1. There is good agreement now that moisture doesn’t arrive until midday tomorrow (11am-1pm) in the metro area.
  2. Precipitation forecast is quite a bit lighter than what we were expecting 24 hours ago.
  3. I would hate to be a school administrator in this situation
  4. THERE IS A DECENT CHANCE THIS WILL NOT BE A CRIPPLING METRO-WIDE SNOW/ICE STORM

 

I’ve gotta tell you, this system coming in tomorrow has a bit of a “bust” potential.  By that I mean there are several signs (as mentioned above and more below) pointing to a lower impact event for our metro area roads and there is also a decent chance some of us in the metro get very little snow OR freezing rain.  Don’t get me wrong, there should still be plenty of icy roads tomorrow and I think freezing rain could be a big issue by tomorrow evening for some areas, but not the “frozen hellish metro area” that I was thinking 24 hours ago.

THE FORECAST

WINTER STORM WATCH continues from the NWS.  A Watch means conditions are favorable for an event.  This could be converted to either a Winter Storm Warning or Winter Weather Advisory (not as big a deal) later today

Dry and turning extremely windy tonight and Thursday.  Peak gusts 70-80 mph in western Gorge by morning and 40-50 mph eastern metro plus west slopes of West Hills.  The rest of us see gusts 20-35 mph.

Snow arrives in metro area sometime between 11am-1pm.  It could immediately change to an ice pellet or freezing rain mix.

Metro Snow:  Nothing to a dusting far south & southeast metro to 1-3″ way out west of Hillsboro or close to the Gorge.  The rest of us should be in-between.  From Clark County to Longview…similar totals Trace to 3″.

Willamette Valley Snow:  Nothing to 1″ along I-5 Woodburn to Eugene.  A little more west valley, quite possibly no snow east of I-5 (Molalla/Silverton/Lebanon)

Gorge:  Snow arrives midday.  6-10″ possible central/east end, lighter west end.  Lots of freezing rain west end tomorrow evening through Friday AM.  Finally warming late Friday afternoon/evening

Coast Snow:  A little too warm for snow, although could be a brief dusting up around Astoria/Seaside midday…maybe

Metro Freezing Rain:  Regardless of the impact to roads (whether it’s warm enough or not), I think freezing rain will continue on the hills in the metro area and near/in the west end of the Gorge well into Thursday night. It might be just on trees and powerlines as temps hang right around or just below freezing, but that can shut down MAX and cause power outages

 

There are 3 big reasons I’ve pulled back on the forecast quite a bit:

  1. The “freezer door” is open for the next 24 hours (Columbia River Gorge transporting cold/dry air west of the Cascades), but the freezer dial isn’t set that cold.  I know, this blog posting appears to have just run right off the tracks and into a ravine…but hang on.  We’re starting with a warmer atmosphere than we’ve seen in past big events (January 2016, February 2014, December 2008)
  2.  Midday arrival means roads have a chance to warm up a few degrees.  With the strong wind blowing tonight, we’ll barely get down to freezing, then roads will warm to mainly above freezing by midday.  When the precipitation arrives, temperatures will fall back to around 30-32 for most of the metro area, but not much lower.   It’ll be “tough” to get roads to freeze again.  Sure, snow will accumulate on them.  But once we change to freezing rain, temperatures need to be 30 degrees or below to keep a road frozen.  Got it?  As a result I don’t think every single road will be frozen, like we saw back in early January this year and the February 2014 snow/ice events.  In fact it’s even POSSIBLE that many roads stay clear tomorrow afternoon away from the Gorge and in the central/south metro area
  3. Precipitation intensity is far lighter now on all models.  Lighter precipitation (either snow or freezing rain) means a bit less cooling of the atmosphere due to the dry air overhead.  Less accumulation on roads = fewer travel impacts  Check out the ECMWF total precipitation forecast through tomorrow evening at 10pm:

ecmwf_precip_24_portland_7

Wow…Less than 1/2″ precip.  That means even if all snow fell and it all sticks, at most you get 2-4″ in the metro area.  This is through 10pm as well.  The last 6 hours there’s no way it’ll be in the form of snow.  Then take a look at the ECMWF snow forecast:

ecmwf_snow_24_portland_9

Notice the WRF-GFS is very similar:

or_snow24-48-0000

You see the light totals as well.  Your next question may be…why no snow on the east side of the valley and very little in Clark County?  That’s due to temperatures warming in the afternoon up around 2,000-3,000′.  Yes, the fabled warm tongue of air pushing north along the west slopes of the Cascades. Yep, it could be a total snow shutout if you live in Molalla/Oregon City/Silverton/Battle Ground.  It starts too late to stick much midday, but by that time it’s already warming overhead and you miss out on the snow!  Quite possible.

East wind will be very strong tomorrow and it appears it’ll continue through tomorrow night in the Gorge and east metro area. Check out the WRF-GFS for 4am Friday…that easterly flow will still be going near/in the Gorge

slp-48-0000

As a result I don’t expect a sudden warmup in the metro area until early Friday.  Luckily we aren’t starting out extremely cold so by the Friday morning commute it’s likely roads away from the West Hills and Gorge should be just fine.

I know it’s a long post so let’s wrap it up with a few questions…

  1. WILL SCHOOL GET CANCELLED TOMORROW?  Wow, that’s an extremely tough call.  If administrators don’t cancel and snow covers many roads and/or ice at 3pm that’s a problem.  If they DO cancel and most roads remain wet at 3pm…they don’t win either.  Sorry folks, no good answer on this one
  2. WILL THERE BE POWER OUTAGES TOMORROW EVENING/NIGHT?  Possibly in the hills and east metro area (especially east of I-205) with ice accumulating on trees/powerlines, definitely in the Gorge, but they all have generators out there!
  3. IS THERE A BIG FREEZE AHEAD?  No, this morning PDX dropped to 27 and it’ll only drop to around freezing or upper 20s in outlying areas tonight.

Chief Meteorologist Mark Nelsen