The next Pacific storm is forecast to start bringing precipitation to the Columbia Basin and Yakima Valley late in the day Tuesday. A few light snow showers are possible as early as 17:00 but the main show begins later in the evening for Yakima and overnight in the Tri-Cities.
The first band of snow, associated with the warm front, will end early Wednesday morning though showers will likely continue. The next phase comes early afternoon as the cold front moves through. The cold front is expected to bring a mixture of snow, sleet, and freezing rain depending on the location.
A winter weather advisory is in effect for the Tri-Cities, Yakima, and Walla Walla for 16:00 Tuesday to 19:00 Wednesday where two to four inches (5-10 cm) of snow and a glaze of ice are forecast. In Grant and Adams Counties, the same amount of snow is expected without the ice. Hermiston can expect up to an inch (2 cm) of snow and a tenth of an inch (2 mm) of ice.
The strength of the cold pool settled in the Columbia Basin makes for a difficult forecast. Warm air aloft brought by the warm front is not going to scour out low elevation cold because warm air is less dense than cold air. As a result, the warm layer will just skim across the top of the cold instead of mixing down to the basin floor.
While this system is warmer than what has been observed over the last few days, it isn’t that warm. The warm layer may not reach above freezing north of a line stretching from about Toppenish to Eltopia. Precipitation should be just snow in this region.
Between that line and the Horse Heaven Hills it’s not clear what form precipitation will take. Freezing rain is possible once the warm layer is in place overhead before sunrise, but cold air north of the hills may be deep enough for sleet instead.
South of the Horse Heaven Hills the cold pool won’t be as deep and freezing rain is favored. Areas around and west of Boardman might briefly transition to rain before precipitation ends Wednesday evening.
Travel will be difficult during this time period with heavy snow forecast in area mountains and up toward Spokane. Portland and Seattle are forecast to experience a significant freezing rain event Tuesday night, which I cover in this article from Sunday.
Another storm reaches the Pacific Northwest on Thursday for a shot of winter precipitation through Friday. It looks like this will come with a warm layer passing overhead but we’re still a bit out for firm details.
The active weather pattern continues beyond Friday as a series of storms aims this way. The storm track turns more southerly into the weekend for warmer temperatures to essentially end chances of lowland snow for now.
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