One More Sunny Day, Then An Ice Storm For Many of Us

January 5, 2017

3pm Thursday…

The sunshine has been beautiful and the lack of wind (for most of us) has been nice.  But check out those low temps this morning.  It was the coldest temp in Portland in over 3 years:

plot_lows_metro

A cold airmass is sitting over the Pacific Northwest and is going to only partially loosen its grip over the next week.   What????  “I thought it was going to warm up?” that’s you are thinking right?  By “partially” I mean for many parts of the Pacific Northwest east of the Cascades and in the Gorge, this crazy snow/icy winter continues through next week.  More on you folks farther down.  West of the Cascades we have a “transition event” on the way this weekend.  We’re transitioning back into mild & wet weather, but it’s going to be an icy mess before we get into the “warmer” weather Monday.

markwarnings_winter-wx-advisory

HIGHLIGHTS

  • Winter Storm Watch is up for much of the Willamette Valley for Saturday afternoon
  • Clear and cold continues tonight and Friday.  One last sunny day, but reasonable high temps in the mid-upper 30s
  • Strong east wind returns tomorrow night and Saturday in the metro area
  • Moisture arrives Saturday morning in the south valley and central coast and moves north; similar to previous systems.  Precipitation arrival time (it’s still 2 days out)  can only be pinned down to sometime in the afternoon.  We’ll refine that timing tomorrow.
  • Most likely it’ll start as snow, then at some point after sunset transition to freezing rain for most areas west of the Cascades.  I see a Trace to 2″ for most of us in the metro area.
  • Heavier freezing rain (ice glaze accumulating on objects and roads) continues through Saturday night and into Sunday morning for the entire metro area
  • For much of the metro area, this means an ice storm begins Saturday evening and continues through Sunday evening as the cold east wind continues to blow
  • Warming southerly wind to finish the event won’t arrive until Sunday night; although some parts of west and south metro, as well as the Willamette Valley may warm a bit above freezing Sunday PM.
  • There is a possibility the central/eastern Columbia River Gorge doesn’t get much above freezing until later next week.  More on that below.

IMPORTANT NOTES

  1. Finish your traveling and errands (anything else that involves moving around on roads) by midday Saturday
  2. It may briefly be wet on roads when it starts Saturday PM, then freeze up after dark
  3. Plan on staying home Sunday

 

The downtime has been nice today and tomorrow will be a slow weather day as well…just sunny & chilly.   But the weather action picks up again on Saturday and seems to continue through next week.

Cold air is firmly entrenched over the Pacific Northwest with high pressure centered east of the Cascades.  The high is quite a bit weaker than 24 hours ago so easterly wind through the Gorge has backed off.  Check out the 3pm temps though!

plot_temps_orwa

East of the Cascades most areas didn’t even make it to 20, and some only in the single digits.  That’s because ALL of eastern Oregon and Washington is covered in snow:

jan5_snowcover

This plays a large part in the forecast for the upcoming week.  As low pressure approaches the coastline Friday night and Saturday, pressures lower west of the Cascades and the strong easterly flow returns.  With such a cold low-level airmass pouring into the metro area and north Willamette Valley, we’re going to have trouble getting above freezing Saturday, especially with thickening cloud cover.  The moisture arrives, now a bit earlier on models, at some point Saturday afternoon.  I think we’ll see a snow start for most of us based on the depth of the cold air and lack of a warm push higher up until after 4pm.  But during the evening the snow level jumps up to around 4-5,000′ west of the Cascades.  That’ll turn our precipitation to freezing rain for any spot west of the Cascades that is below freezing (most areas).

From Saturday evening through Sunday evening precipitation in the Portland metro area and maybe as far south as Salem will be in the form of liquid rain, with temperatures below freezing.  The reason I lowered high temps to around freezing Sunday is due to all models showing the “freezer door” being wide open during that period.  That low-level cold air from the snow-covered terrain east of the mountains will be funneled through the Columbia River Gorge…actually more like “blasted through”.  Unfortunately this means we have an ice storm on the way, potentially as destructive as what we saw one month ago on the east side of the metro area.  Thickest glazing will be on the hills and central/east metro area where temperatures will be coldest, due to that easterly wind continuing.

When do we warm up above freezing?

For the metro area, that should occur Sunday evening/night as a cold front moves by overhead, greatly weakening the easterly pressure gradient and possibly evening turning it light westerly in the Gorge.  At the same time a mild southerly wind should move up the valley.  This should end the freezing rain threat WEST of the Cascades.  But I’m doubtful the cold air totally scours out of the Gorge.  That leads to a 2nd storm coming Tuesday.  This one is a very wet soaker with a surface low pressure that tracks right up into Oregon.  In this case the gusty east wind returns and could give at least the central/eastern Gorge a 2nd even bigger snow/ice storm.  The WRF-GFS and ECMWF are both hinting at 1.5 to 2.5 feet of snow in the Gorge between the two storms!  Lots could change before that time of course, but it’s possible winter is going to get tougher the next week east of the mountains and in the Gorge.

Enjoy the bright sunshine Friday, and use the calm weather to prep if you live in the Gorge or hills (generator, gas, firewood, chains, etc…)

Chief Meteorologist Mark Nelsen