Noon Wednesday

I've heard the grocery stores are getting crazy now? Folks...this is a 2 day event at most for the vast majority of us west of the Cascades. You aren't going to be locked in your homes for a week... Although it's a different story in the Gorge. Read on...

KEY POINTS

Temperatures should remain above freezing tomorrow until after sunset west of the Cascades. Roads will most likely be just fine until sometime after dark. But since we don't know EXACTLY when it'll freeze in your neighborhood, MAKE PLANS ASSUMING ROADS COULD BE FROZEN AFTER 5PM. Either turning icy from freezing rain or snowy (especially north/east metro)

All of the metro area freezes tomorrow night. We should wake up to pockets of glaze (south metro) on roads Friday morning or snowy roads (all other parts of town). Enough for sledding central/north metro.

Expect a Trace (south metro) to 3" snow out of the "first wave" ending Friday morning

Roads remain partially frozen during the daytime Friday as temperatures remain at/below freezing.

An additional 3-8" snow could fall later Friday through Saturday morning with a "second wave" of precipitation. Heaviest will be north and east metro. From Newberg to Wilsonville to Molalla to Sandy there may be no snow, just pockets of freezing rain

This may be it for snow in the metro area, giving us a storm total of a Trace to 12" in the metro! Very little snow south, but Scappoose, Longview, Clark County, & East Portland get a lot.

The 3rd wave (Sunday) should be mainly freezing rain Saturday evening through Sunday morning and only near Columbia River in central/east Portland. This is the usual freezing rain area during typical wintertime events. You aren't getting out of this until Monday morning if you live around Camas, Troutdale, & Gresham.

Expect some thawing Saturday afternoon south/west metro, much better roads. Then substantially more thawing on roads everywhere except near Columbia River and Gorge Sunday.

For the majority of the metro area, most of the "action" (falling snow & freezing rain) will be done by Saturday afternoon.

TECHNICAL DETAILS

I know I've always been a bit biased with regard to the ECMWF model, but it has been leading the way for days with this event. It's been best tracking systems farther north than other models Thursday through Sunday and that continues this morning. It has been much more reasonable not only with upper-level temps but low-level cold air too. Remember just 2-3 days ago when it was alone NOT forecasting a major wave of cold arctic air?

Luckily the WRF-GFS, typically a stellar performer, and morning 12z run of Euro, are now in pretty good agreement. An arctic boundary (stationary front) will be sitting across extreme NW Oregon from tomorrow evening through at least midday Saturday as several waves of moisture move overhead. Precipitation type (rain, snow, ice pellets, freezing rain) in any one location will be dependent on how thick that cold layer is over your part of the region. Generally the farther north you go, you're deeper into the cold air = more snow. Farther south, very thin layer below freezing means you get freezing rain. Of course if that thin cold layer is only down to 33-35 degrees, you get normal liquid rain. Unfortunately 2.5 million people live in the metro area directly under that thin dome of cold air pouring out of the Gorge these next three days.

BTW, The only difference between freezing rain and regular rain is that the temperature is below freezing in the first case and that liquid freezes on contact.

The first surface low moves toward the central Oregon coastline tomorrow morning, pulling cold air out of the Gorge. It's going to take until after dark for most of us in the metro area to drop to freezing, so I'd be surprised if roads freeze up before the evening commute is finished. Here's the progression of things based on the WRF-GFS model. Euro is similar...

7amThursday.gif

By 7am Friday morning the low has dissipated, cozying up to the central Oregon coastline. East wind is raging through the Gorge and cold air is everywhere north of Salem and Tillamook

7amFriday.gif

Precipitation is turning showery Friday am & midday. Snow total through this time from WRF seems reasonable. Although precip seems a little light up in Clark County

wrf_snowthroughfriday7am.gif

By late Friday the "second wave" is approaching, a bit farther north

4pmFriday.gif

And by Saturday morning we've seen a ton of precipitation, but with the low farther north a warming southerly wind has arrived on the coastline and (overhead) in the central Willamette Valley

7amSaturdayWRF.gif

That's why I don't expect snow out of the 2nd wave south of metro area. This system knocks down the cold surface high quite a bit as well. By Saturday 4pm it looks like this...cold air is just barely hanging on in the metro area.

4pmSaturday.gif

By this point, the ECMWF snow forecast looks good...this is total snow all the way through 7pm Saturday. A lot of snow on the ground from north Portland into Clark, Columbia, Cowlitz counties. And the Gorge has been buried by 12-24" at this point. Maybe more

eurosnow_7pmSaturday.png

WRF-GFS has slightly different placement, but the same general idea... very little snow on the coast out of this event (some up north), and from Salem south.

wrf_snowthroughsaturday4pm.gif

We may get a significant ice storm southwest and south metro down into the western part of the Willamette Valley. We will see, but these numbers are likely far too heavy.

euro_freezingrainbySaturdayPM.png

Now check out 1pm Sunday...here comes the "third wave" with a low farther north. One last pull of cold air through the Gorge Sunday morning/midday. It's unlikely anywhere west of the West Hills or south of Lake Oswego to Clackamas would get freezing rain out of this. It's really becoming a "gorge-centric" event by this time. Lots of freezing rain later Sunday in and near western Gorge.

1pmSunday.gif

Why will this event end so quickly? Because it's not a case where a surface low is swinging by offshore. This time it just plows right across southern Canada since the upper-level pattern is becoming very progressive. A relatively strong and "warm" west wind is blowing in the Gorge Monday. #RIP_FEB2021_SNOWSTORM

10ammonday.gif

So that's the plan for now. 3 more important notes:

  • 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!
  • We will be recording a FOX12WEATHER podcast with all four meteorologists early this afternoon and it should drop into your Apple Podcasts this evening
  • Make sure you are following me on Facebook at @MARKNELSENWEATHER and Twitter @MARKNELSENKPTV

Chief Meteorologist Mark Nelsen

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