Sunday Morning: First Snow Sighting Of Winter For Many of Us

January 21, 2021

6pm Thursday…

If you haven’t left the lowlands this winter, most likely you also haven’t seen a single snowflake. February is less than 10 days away! That’s unusual in our climate. Typically we have a close call or two, if not real sticking snow, by this point in the winter. Not this year, it’s been very mild. But if you are up before 10am Sunday, it appears there’s a decent chance you will at least SEE snowflakes in the air. Sledding in the lowlands? Unlikely.

For the short attention span (TLDR) folks…

Winter Weather Highlights

  • Between 4-8am Sunday, precipitation arrives across NW Oregon and SW Washington. Most likely it’ll be a rain/snow mix in the lowest elevations (where most of us live)
  • There’s a decent chance it falls as mainly snow for at least a few hours 7am-10am, even in the lowest elevations. It could get very exciting weather-wise for a few hours!
  • Temperatures remain ABOVE freezing Saturday night and Sunday = little or no sticking. If it falls heavily enough, it might briefly accumulate on cars/barkdust etc…
  • IF you live up around 1,000′ and above, there’s a better chance your neighborhood turns totally white for a few hours.
  • IF you live around 1,500′ and above, expect 1-3″ Sunday morning through midday. There are no spots in the metro area that low.
  • Highways/roads will remain snow-free Sunday in the metro area, except at/above 1,000′ where they could briefly turn snow covered.

THIS SHOULD BE A “CONVERSATIONAL SNOW” EVENT FOR THE LOWEST ELEVATIONS. That means everyone will be talking about it; plus posting Instagram/Facebook pictures of their dog/cat/pig/chicken/duck running wildly about outside, but it won’t affect our lives otherwise.


TECHNICAL DETAILS

A cool upper-level trough (the first of several) is sliding down north to south along the West Coast. This system is headed for California and far enough offshore that we’re seeing almost no showers inland. A mainly dry and cool airmass settles over us Friday & Saturday. Drier air filtering in from Canada gives us LOTS of sunshine Saturday; enjoy that day after a cold start. We’re not getting a “cold blast of air” by any means, just a bit colder.

By Saturday night another cold upper-level trough is sliding south along the BC coastline. A cold front then moves inland midday Sunday. Here’s a loop from the ECMWF model showing the movement from 1am to 7pm Sunday. Not exactly a “storm” eh? All models have been showing this scenario for several days and all agree on the timing; pretty good for 3-5 days ahead of time.

Freezing levels Sunday morning will be up around 2,000′ or so with this system, which typically means we might see snowflakes down to maybe 1,000′ and just a rainy Sunday morning in the lowlands. But a few things are different Sunday morning which should bring those flakes lower:

  1. Overnight cooling, while minimal, means this system comes in at the coldest time of day
  2. No significant “warming” onshore wind. There’s no cold/dry wind blowing out of the Gorge, but there’s no push of warmer air before 10am either. It should be mainly calm Sunday morning, at least for a few hours.
  3. There are signs we get a burst of heavier precipitation between 7-10am. Heavier precip = better chance for flakes to survive a longer fall through the atmosphere

These all point to a setup where snowflakes may survive falling all the way down to the valley floors west of the Cascades (less likely along the coastline) for a few hours Sunday morning. The reliable WRF-GFS model from UW shows the above freezing temps through Saturday night. At 4am it’s in the mid-upper 30s in Portland. This isn’t a setup where precipitation arrives at sunrise after a frozen night.

But as precipitation starts falling, look how surface temp drops to 33-36 degree range

Then 10am

That’s pretty much a snow sounding; at/below freezing except for the lowest 500′ or so. By 1pm Sunday, the cold front has passed, mixing (warming) the lowest layer of the atmosphere with a southwest or westerly wind. At that point we’ll just see rain or mixed rain/snow showers. It appears we have .25 to .50″ precipitation to work with, enough for 1-3″ in higher elevations where this falls as snow and sticks.

Models ALWAYS struggle with predicting snow totals in these marginal events. This morning’s ECMWF model continues the “little or no sticking snow” idea; you need to be up/above 1,000′ (or 1,500′) to make a snowman this time around

Note the coarse resolution here. I’ve purposely left it “unsmoothed” so you can see the model resolution. It doesn’t see the West Hills or Chehalem Mtn. at this 9 kilometer resolution. It also doesn’t “see” the Columbia River gap between Woodland and Longview, thus painting a bunch of snow for Kalama, Rainier, Longview, & St. Helens. It “thinks” the hills of Columbia county OR just merge into the hills above Kalama & Woodland. Higher resolution models (4km & lower) DO show those features, but we don’t have those today. They run just 72 hours out in time and only cover to 4am Sunday.

Alright, so that’s your first “big snow chance” for this season. That was a joke, it’s not a big snow chance. We MIGHT be close again early next week (either Monday morning or Tuesday night), but we can discuss later.

I still want to be clear that this is the not the beginning of a cold/snowy weather pattern. Sure, we’ll be getting more regular frost and overnight freezing. But no sign of an arctic blast through at least the first few days of February.

I probably won’t post tomorrow considering how minor this event will be; time to get out and enjoy the wintry outdoors. I’ll definitely be back with an update Saturday.

Chief Meteorologist Mark Nelsen