There comes a time at the end of these cold east wind events where the airmass pouring out of the Gorge becomes so thin that parts of the metro area "pop out" into the milder air above. I've seen it happen each time.
That appears to be happening in the higher elevations of the metro area right now. Chehalem Mountain is up to 37 degrees. Top of Mt. Scott from 28 at noon to 32 now (still rising), Larch Mtn. Washington has jumped to 38 with a south wind (and rising). These areas are all near the 1,000' elevation. Fascinating meteorologically because up until early afternoon these were the COLDEST spots in the metro area. That's because they were higher up in the cold westward flowing air from eastern Oregon/Washington. Folks, this brief cold/ice/snow episode is just hours away from finishing...Once it warms in the hills around town the game is just about over.
Notice ALL metro temps are at/above 30 degrees now. The only 20s are left in the western Gorge, around Corbett and east of Washougal.
Don't get me wrong, at 30-32 degrees ice can still accumulate on trees and powerlines = bad. But it can't last much longer now. The snow level is up around 5,000' this evening in the "warm" airmass overhead, that's why we're seeing liquid raindrops falling through this thin cold layer and freezing on contact (in spots) instead of snow.
The pressure gradient is 7-8 millibars easterly through the Gorge, and the wind is still blowing hard out there, confined to a layer less than 2,000' thick. That goes to zero around 9-10am. In fact a westerly surge works through the Gorge later tomorrow afternoon = much warmer!
So we've got a few more hours of icing, then not much rain at all after 2am as this system moves off to the east. It'll be mainly dry for the morning commute. As mentioned in the previous blog post, I expect a southerly surge of wind up the valley after 4am as a surface low pressure tracks by to the north. You can see the switch and temperature jump into the 40s sometime after 7am in Portland from our GRAF model
- Expect a bit of additional icing the next few hours mainly east of I-205 and into the Gorge. Still a bit more in higher elevations of SW Portland & the West Hills, but most of forecast ice glazing on graphics below has already happened. We should be more dry than wet after 2am and through the morning commute.
- Temperatures hover between 30-34 in most of metro area through 6am, then jump into the low-mid 40s between 6-10am. Expect quick thawing by late morning. Lots of water all over the place...
- 6-10" total snow in the Gorge through morning with temps below freezing until noon or so. But even there a westerly wind should push all of you up into the 30s by dinnertime and beyond.
- The rest of tomorrow and this week will be uneventful with lighter showers Tuesday, dry Wednesday, then some cool/wet soakers into next weekend. Up to 2 feet more snow will fall in the Cascades these next two days. Oregon will be back to normal snowpack-wise within the next few days! Nice La Niña catch-up.
I'll be on TV at 10 & 11pm tonight...Chief Meteorologist Mark Nelsen