A few showers will continue to fall over the region today, with another couple of inches of snow forecast in the Oregon Cascades by late afternoon. After midnight tomorrow and into Wednesday, a blast of colder air will descend from the north, bringing the possibility of further light snow with it.
Predictions for the next system, which is likely to arrive early Thursday into Friday, are for temperatures to decrease somewhat while bringing another wave of precipitation before the New Year weekend.
As of late this morning, shower coverage has lessened, with the most extensive coverage being off the southern WA coast near the surface low that is being fed by cold offshore air.
As they go farther inland, the rains become much weaker. This may continue over the next couple of hours, although the shower coverage will be reduced as a result of the loss of the cold air input.
The southerly breezes that have been blowing up through the Willamette valley into the low have enabled temperatures to rise slightly above anticipated levels.
High-resolution models may be catching up on this, as multiple areas of increased shower coverage are being seen this afternoon, reaching into the Oregon Cascades and beyond. This will very certainly result in another 1-3 inches of extra accumulation in that area.
The Pacific Northwest will be hit by a frigid arctic blast tonight, thanks to a shortwave that is falling out of Canada's Alberta province. Another bout of mostly light snow will fall throughout the region as a result of this.
In addition, this surge will strengthen easterly winds in the Columbia River Gorge and the Cascade Mountains late tomorrow and into Wednesday. The Gorge will see the greatest winds, particularly early in the morning tomorrow, with gusts reaching 30 to 40 mph in the western section. Some of the harsher gusts may reach as far east as the Portland-Metro region, bringing wind chill values down to the low teens.
In terms of the next weather system, which is expected to arrive Thursday morning and continue through the day, the cold arctic air that has been pushed in from the north may remain in place for a longer period inland than what the models are indicating before the warmer air from the west moves in.
This might result in a brief period of mixed precipitation (snow, sleet, freezing rain) before the airmass warms up enough to produce rain at lower altitudes due to southerly breezes warming the airmass enough to produce rain there.
The risk for freezing rain seems to be limited to isolated valleys in the Coast Range and Willapa Hills, as well as into the Washington I-5 corridor and the Portland-Metro region reaching into the western end of the Gorge, according to the latest information.
However, there is just a 10-20 percent possibility of seeing it, and it would only be visible for a very little period, maybe between the early morning hours of Thursday morning through the early afternoon.
And even if this were to occur, the accumulations would be quite little.