



By 10 AM on Wednesday, cold air is entrenched over the Northwest, with a very strong north-south pressure gradient that will create strong northerly and northeasterly winds.

It is now becoming clear that a major cold period will occur next week, cold enough that if you lack enough refrigeration foryou holiday meal, you can simply put the food outside.Highs will only rise to the upper 30sF on the western side of Cascades and there will be substantial snow in the mountains. But will there be lowland snow? That I will explore later.The models are now consistent in bringing cold air southward, as illustrated by the WRF model forecasts shown below, which present sea level pressure (solid lines) and temperature about 3000 ft above the surface (color shading). Next Tuesday at 1 PM, cold air (blue colors) is entering the region, pushed southward by high pressure in Canada and a low pressure area off the northern Oregon coast).The cold is "in the bag", based on lnsemble predictions in which the models are run many times. The forecast temperatures at Sea Tac, based on the European model, indicates highs in he low 50s this weekend (pretty typical), but then the "cold turkey" comes in Wednesday and Thursday.The cold wave will be initiated by the movement southward of an upper trough (see below for 7 PM Tuesday), but it is too broad and offshore to provide western WA with lowland show--perhaps a few flurries. There is a bigger risk for PortlandThe WRF snow accumulation forecast though 4 AM Thursday shows snow on the slopes of the Cascades, but very little over the Puget Sound lowlands....Portland has a better chance.I know some of you love lowland snow (or fear it), but November is early for the lowlands. We need colder air, with an upper level shortwave and its surface reflection that would result in easterly flow over the Cascades, which tends to cause drying over the lowlands. But the situation is still well out in time and things can change. Stay tuned.