Drew & I just spent the last 1/2 hour doing some serious surgery on the forecasts…any forecast page that involved the time between 7am and noon tomorrow needed some bandaging or maybe even total replacement. Some of those forecasts were on life-support anyway.
Up until the 00z model runs, it sure looked like the cold air wasn't going to stick around long, plus the precipitation arrived at the same time the good southerly wind arrives. Here's what I see now that makes me think a widespread snow is likely in the morning here in the metro area:
1. Nice dry airmass over us…great for evaporational cooling.
2. On several mesoscale models, including our RPM, they show the sudden evaporative cooling in the north Valley and Metro area sometime around 8-10am producing a "meso-high" pressure right over us. This thing was there just a bit on one 12z model, but now I see it on 3 models. This would imply for a couple hours there may be no or little southerly wind at the surface here in Portland. That's a big one considering the combination with #3.
3. A nice burst of moderate precipitation at the same time as #2.
4. In general it just looks good to my weather eyes for a quick morning snowfall.
One big kink in the plan is that several of the models show warming well up there, maybe above 2,000'. This may give us ice pellets and/or freezing rain (less likely) at the same time. My gut feeling is that it'll be all snow, but I thought that once with a system that turned out to be all freezing rain too! So Drew and I threw some ice pellets or freezing rain pockets in as well.
I still like the idea of gusty southerly wind and rapid warming to around 40 degrees beginning around noon. I also notice a nice westerly surge through the Gorge at the same time. This will be the first time The Dalles has been above 35 in about 2 weeks!
Gotta go! Mark Nelsen