7:30pm Sunday...

Well, well...here we are, heading into mid-February and suddenly my app is full of snow. Our FOX12 OREGON app looks like this on my phone

appforecast.jpg

7 to 13" of snow late this week and below freezing temps for at least two days? That would shut the city down wouldn't it?

Notice our "official" 7 day forecast below which is also on the app. Cold temps here too, but no specific snow accumulation forecast. There's good reason for that. As I've mentioned in the past, weather app forecasts are just output from complicated numerical simulations of future weather (the models). No human is touching that app above, but of course we put much more thought into what you see below.

Forecast 7 Day.png

It seems increasingly likely that SOMETHING is in the works along the I-5 corridor for late this week.   Some sort of snow/ice/cold “event” is on the way for some part of the corridor between Seattle and Eugene. Maybe even out to portions of the coastline.

It’s still too far out (4 days) to know how things will play out in detail, but at this point it’s fair to make these statements:

  1. Some, or maybe a large, part of western Oregon and/or western Washington lowlands will get a significant snowfall (2-4″+) within the next 7 days.
  2. The chance for a widespread "arctic freeze" is low right now in our viewing area west of the Cascades. At this point widespread temps below 20 degrees appear unlikely.
  3. A snowstorm is very possible Thursday-Saturday in the Columbia River Gorge, possibly freezing rain too.
  4. Start planning aheadWhat if there is some sort of significant snow/ice event Thursday-Saturday?  How would you deal with it if that’s the case?  It's best to have a plan, even if it all stays up in Western Washington in the end.
  5. There is still plenty of time for this to "fall apart" and nothing happens since it's still 4+ days away. You may remember a year ago (January 2020), a similar "big event" like this was in the forecast. We pulled out of it (#SnowstormCancel) just 2-3 days ahead of time. Nothing happened.
  6. STAY TUNED THIS WEEK AS I'LL BE BLOGGING EACH DAY; AND OF COURSE ON TV EACH EVENING. Follow me on Facebook @marknelsenweather and Twitter @MarkNelsenKPTV for more frequent updates.

At this point, we can't make statements like this until we get closer to the event.

  •  I expect 6-10" snowfall over the Portland metro area Thursday through Saturday morning"
  • Portland will be a frozen hellish white mess Thursday through Sunday
  • 3" will fall over Sheridan but 12" in Molalla"

This graphic summarizes it well

Snow Look Ahead General Info.png

TECHNICAL INFO

There is a lot of cold air just to our north. Most of Montana east of the Rockies is below zero. Very cold in central/northern British Columbia too.

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Over the past few days, models have been grappling with how far south to bring that cold air into the Pacific Northwest the latter half of this week. The problem is that we've got two converging flows of air in the upper atmosphere to keep an eye on. Right now up around 18,000'...

7pm500mb.gif

Cold arctic air is bottled up generally along the northern arrow. Then a moist and mild flow cutting in to our south. Jump forward to Thursday morning. That southern stream is pushing a bit farther north. One would think it's not an issue right? A bit warmer high up in the atmosphere...mild.

4amThursday500mb.gif

Correct, mild weather likely through Wednesday night or early Thursday IS the forecast. But then look at what's happening down where we live near sea level. An approaching low pressure center from that "southern stream" pulls cold arctic air south through Washington, and through the Columbia River Gorge on Thursday. If this were to happen, temperatures would DROP on Thursday and rain changes over to widespread snow in the metro area and all other points north and east. Remember this is just one model of many.

wrf_thursdaypm.PNG

That IS the perfect setup for a major snow or ice storm for the Portland area. This is the WRF-GFS model, which is based on the USA's GFS model but the ECMWF model is similar. You can see why it's such an issue to make a detailed forecast this far out! Wow, east wind + blowing snow and 20s in Portland, but mild south wind and 40s south of here in the Willamette Valley. Actually there would be an area on the boundary between the two that gets ice pellets and freezing rain. REMEMBER THIS IS ONLY ONE MODEL RUN FROM ONE MODEL. This isn't my forecast.

ECMWF Clouds Rain Snow.png

As always, placement of that surface low approaching the coastline will be critical in determining who gets snow Thursday and early Friday. East wind = cold, south wind = mild. We have lots more information nowadays that can be helpful. Check out this Thursday afternoon forecast from 51 different ECMWF ensemble members. It shows the low center (and depth) for each

ecmwf-ensemble-avg-nw-mslp_with_low_locs-3088000.png
  • If the low stays south of ~Tillamook, we get something frozen (snow or freezing rain) in the metro area.
  • If it goes farther north, Portland would only get some brief snow or nothing with a milder south wind. Snowstorm is up in Puget Sound and Chehalis in that case.
  • BUT, if it goes farther south, like several of those lows in the graphic down around Coos Bay? That's a snowstorm all the way from Longview to Eugene. Possibly out along the coastline too!

Hopefully you get the idea...there's far too much up in the air 4 days ahead of time to make an educated guess at this point. In the next two days models will come together and we'll have a better idea. Lots of twists and turns ahead! Plus we'll have to figure out late Friday through early Sunday when ANOTHER LOW approaches the coastline.

I've ignored the extremely cold GEM (Canadian model) for now. It's the only one thinking a lobe of the polar vortex in the upper atmosphere will rotate down over the Pacific Northwest! It would be an all-time cold spell for late winter in that case.

Chief Meteorologist Mark Nelsen

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