The coldest night of the winter for many of us westside is in progress right now. Yes, some places were colder earlier in the winter, but it’ll be close. Still waiting for the north wind in the Valley and east wind in the Gorge to completely decouple from the surface. With dewpoints around 10 many areas, it should be easy to get down into the teens.
So we’ve got moisture moving in tomorrow night, cold air in place, and a perfect setup for a brief snowfall? That forecast above is the 72 hour period ending Monday afternoon. Note it shows possibly a dusting (spotty) in the Valley. Possibly, but I see two things working against it (and mesoscale models seem to agree) getting more than a dusting:
1. Moisture is very slow to move in and quite light from late Saturday evening through daybreak Sunday…just a few hundreths of an inch. Not the best if you want really good evaporational cooling. That moisture dropping into the cold air and evaporating, thus taking “heat” out of the airmass. Temps cool as that occurs.
2. Onshore flow commences by sunset tomorrow, picking up, and by Sunday morning we’ll have a breezy southwest wind blowing up the Valley and THROUGH the Gorge too. Not a real warm airmass, but should be enough to lift the snow level up to 1,000′ or so.
Once we get past that, the threat for widespread snow in the LOWEST elevations is over, but it’ll be close off/on through the next 7 Days. If you think of a late-winter La Nina weather pattern, this would be it. Many feet of snow in the Cascades and even down into the foothills through the first week of March. Models show 2-3ft. of snow just from Sunday midday through Monday afternoon! It’s unusually cool westerly flow through the whole 7-10 day period. Looks like Monday night the snow level is back down around 1,000′ again (briefly).
Chief Meteorologist Mark Nelsen