More Musings on Cold and Snow

What a change a day makes. Last night's 00z models were somewhat disappointing for us here in the Pacific Northwest, sliding the brunt of the cold (and all chances of snow) off to the east. The 12z Euro reinforced that idea.

But some magic has been happening in model land today, and the clear trend in the ensemble mean couldn't paint a better picture. In the four runs since and including the 00z GFS, the coldest 850mb temperatures for the ensemble mean in Portland have been -7C, -9C, -10C, and on the latest 18z ensembles, as shown above, -12C. That is an incredible ensemble mean for a time period less than 5 days out. Seattle, likewise, has trended, respectively, from -9C, -13C, -13C, -16C. Wow!

With the further west solution, the 18z GFS produces another area of low pressure along the coast after the initial cold surge Sunday night. As this drops southeastward, moisture associated with the low dumps quite a bit of snow in the northern and north-central Willamette Valley. This is just one run and specifics will change before all is said and done, but our chances for snow on Monday are now much higher than they seemed 24 hours ago.

Tuesday and Wednesday will likely be dry with a ridge building in, but should still be cold with east winds through the Gorge (and a remaining cold airmass over Seattle). There's no agreement on how or when we transition out of the cold. It could just be a gradual warm up with dry conditions, could be a messy overrunning snow or ice storm, or somewhere in between (moderating, then just rain?).



In the closer-range, it appears there is an outside chance that someone in Northwest Oregon or Southwest Washington could see a band of snow set up Saturday night. A band of moisture swinging around the low offshore could stall out in the area, and with heavy enough precipitation rates and a cold airmass, not to mention light offshore flow in the Portland area, we could see the same type of "surprise" we saw last night, where snow levels were a good 1,500 feet below predicted in the heavier bands of precipitation. Except this time, that would take the snow level all the way down below 500 feet... possibly near the surface. It would be a very borderline thing, but the potential is there.