Tomorrow brings a nice shot of winter back to much of the Northwest with an upper level low sliding across Oregon tomorrow afternoon and evening. Snow levels have been holding around 2000 feet tonight and should stay that way through tomorrow. Here’s a picture of the low at 500 mb at 10p Tue night.
Temps at 500 mb are between -34 C and -38 C which is pretty darn cold air! It’s very densely packed as well which could aid in bursting showers below it. In fact, here’s what the precip map looks like at this same time:
Some good looking showers bursting through the area at the same time as well. So here’s the thing: Heavy showers can pull the snow level lower than it currently “sits” at because as rain falls some of it evaporates (virga) while some of it hits the ground. The droplets that evaporate cool the air surrounding the drop as it “dries”. It’s a process called “Evaporative Cooling”. It takes a lot of heat to evaporate water and so when drops evaporate they use up the heat in the surrounding space between drops which cools that tiny parcel of air. Well, if you’re drying millions of water droplets in a small space (relatively), you’ll cool the overall temperature of that air. That’s how when we have very cold systems in the winter here in Oregon, we can see rain showers mix some wet snow flakes in with the rain, especially when the rain really intensifies.
So do we see snow below 2000 feet? Likely, but it’ll be very brief, maybe down to 1500-1000 feet and much of that in the higher hills around the valley won’t stick. But just to peek, here’s the snow output for that same time:
Looks like some nice snow showers for folks in Vida, Blue River, maybe even a light inch or so near Oakridge. Passes should see 2-5″ when it’s all said and done too. Here on the valley floor, we’ll just be cold and damp Wednesday morning, but with lows likely near 29-30 degrees, slick and frosty as well.
~ Justin Stapleton
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