11am Thursday...

Things have sure changed this morning haven't they? It's a cold and icy day...forget about the 45 degree sunshine. A cold east wind has spread out of the Gorge and throughout the metro area. Temperatures are below freezing now through the Gorge with snow falling at the east end and freezing rain west end. It has begun...

In the metro area temperatures are holding steady due to the midday "heating". In the hills and close to the Gorge some areas have dropped below freezing which means freezing rain to start this event. That's because the "real snow level" is up around 3,000' west of the Cascades. Until the depth of cold air pouring out of the Gorge is deep enough to meet that, precipitation stays liquid. I think that will happen by 4pm at the latest. In general, the forecast is on track. Road temperatures (due to midday heating) are remaining above freezing in most areas, but that will change as we near sunset. Cold air pouring out of the Gorge is battling the strengthening February sun energy. 11am temps...

web_temperature_ORWA (8).jpg

KEY POINTS

A major snow & ice storm will gradually ramp up this afternoon from the Portland metro area north and continues through Saturday midday. This could be our biggest February storm on record and should be our most serious (widespread) event since December 2008. I think this will go down with January 1998, January 2004, & December 2008 as one of "the big ones" that meteorologists remember. The only difference? This is so late in the season that it'll be much easier to warm up early next week.

Expect a changeover to mainly snow for most of metro sometime after 1pm, for sure by 7pm. Some areas south metro may stay as liquid rain, which means freezing rain after 5pm as temperatures drop

  • ASSUME THE EVENING COMMUTE WILL BE ICY WITH ROADS FREEZING UP. DON'T GET STUCK OUT ON THE ROADS! In some areas there will be ice from freezing rain first before a changeover to snow = slippery.
  • Roads will generally be icy/snowy from this evening through at least Sunday morning. Some improvement is possible Saturday daytime if precipitation tapers off, especially west and south metro
  • Expect a Trace-1" (south metro) to 4″ snow out of this “first wave” ending tomorrow morning
  • An additional 2-10″ snow could fall tomorrow night through Saturday midday with a “second wave” of precipitation. Heaviest will be across the middle of the metro area and north. From Newberg to Wilsonville to Molalla to Sandy there may be very little snow with more freezing rain
  • The vast majority of snow will fall by midday Saturday. Giving us a storm total of a 2 to 14″ in the metro! The low number will be south metro , but anyone in a line from Hillsboro to Gresham and north gets nailed with the deep stuff.
  • The 3rd wave should be mainly freezing rain Sunday afternoon/evening through Monday morning. This might be mainly near Columbia River in central/east Portland. This is the usual freezing rain area during typical wintertime events.
  • Expect some partial thawing Saturday afternoon south/west metro; better roads. Then more thawing on roads everywhere except near Columbia River and Gorge Sunday. But it doesn't matter if we really get 8-12" snow widespread. That's obviously not going to get plowed off many roads.
  • For the much of the metro area, most of the “action” (falling snow & freezing rain) will be done by Saturday afternoon. Quite a storm!
  • THERE WILL NOT BE WIDESPREAD WARMING AND MELTING UNTIL SUNDAY NIGHT OR MONDAY MORNING WHEN OUR WIND TURNS SOUTHERLY ACROSS ALL OF THE METRO AREA

TECHNICAL INFO

Nice to see models/maps looking almost the same today!

1st wave of precipitation arriving this afternoon/evening. Not very heavy. Surface low pressure right up against central coast tonight and tomorrow morning, drawing arctic air through the Gorge

wrf_4amfriday.gif

Total snowfall on WRF looks good for this first event. Enough for some sledding in spots tomorrow morning, but not exactly a huge storm at this point. We're frozen in tomorrow morning; 20s in metro area.

wrf_snow_10amfriday.gif

That low dissipates, but a 2nd stronger one is rapidly approaching tomorrow afternoon and evening. Pressure gradients tighten tomorrow evening, giving a massive 12-14 millibar gradient through Gorge and heavier precipitation arrives...here we go!

Inkedwrf_10pmfriday.gif

By 10am Saturday that low has moved right up against Astoria. If we didn't already have cold air in place, this wouldn't be a snow setup for us...low is a bit too far north. But we've got a deep cold layer pouring out of the Gorge; we're still frozen.

wrf_10amSaturday.gif

After this point we're into a typical post-frontal showery airmass = not much more accumulation midday Saturday through midday Sunday. Total precipitation so far? Over an inch in parts of metro area

precip_bysundayam.gif

Notice some spots get less (parts of Clark County?). So our forecast of 8-14" in the areas that remain snow through this entire event looks good. Total snow by midday Saturday from ECMWF model (a bit "wetter/whiter" compared to 24 hours ago). THIS GENERAL SETUP HASN'T CHANGED FOR DAYS FROM THE EURO MODEL. Quite a line across south metro to little/no snow. Wow!

ecmwf_totalssnow_final forecast.png

That low Saturday is far enough north that would typically get a light southerly breeze in the valley south of Portland. But cold air is too entrenched, that seems unlikely. So we'll stay frozen Saturday, but any sunbreaks and a stoppage of precipitation should let roads improve a bit. Same for Sunday.

12z WRF-GFS snowfall map is similar, ending Saturday afternoon.

wrf_totalsnowbysaturdaypm.gif

As mentioned, I expect a damaging ice storm south/southwest metro tomorrow night through Saturday morning due to thinner layer of cold air. This includes south of Hwy 26 westide over to Lake Oswego to Oregon City. A messy mix of snow and freezing rain.

By Sunday 10am the 3rd wave is approaching, once again drawing cold air back out across far NW Oregon and SW Washington.

Inkedwrf_10amSunday.gif

This one could begin as snow Sunday afternoon/evening, but would likely change to freezing rain Sunday night as warmer air finally arrives overhead. By Monday morning, we're in mild onshore flow and southerly wind for ALL areas west of the Cascades. That's the end of the event, except that we've got 8-14" snow to melt off roads and ice damage all over south and southwest metro...next week will be cleanup time

Inkedwrf_10ammonday.gif

That's it for now...

  • We will have specific forecasts for the Coastline, Valley, Longview/Kelso, The Gorge & Cascades all through our evening shows. We are on FOX12 for an hour at 4pm, 5pm, 6pm, 10pm, & a half hour at 11pm. Also two hours on FOX12PLUS 8pm & 9pm. Find me and the weather team there!
  • Make sure you are following me on Facebook at @MARKNELSENWEATHER and Twitter @MARKNELSENKPTV

Chief Meteorologist Mark Nelsen

Copyright 2021 KPTV-KPDX Broadcasting Corporation. All rights reserved. 

Recommended for you

Load comments