Weather 12-17-19

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The ridge of high pressure that’s been in place the last few days is beginning to shift east this morning in response to a splitting weather system in the eastern Pacific. For today, we will see some isolated areas of fog and low clouds this morning mainly for the Okanogan valley and the Cascade valleys with light south to southeast surface winds. Temperatures in these places will struggle to get into the low 30’s this afternoon. Otherwise afternoon highs in the mid to upper 30’s under variable high clouds.

Wednesday and Wednesday night, that splitting trough of low pressure will then move through the region early on Wednesday with a second trough setting up off the coast. Moisture will be on the increase through the day Wednesday and Wednesday night as the flow turns southwesterly and taps into the beginning of an Atmospheric River of moisture. The chances for light precipitation will be on the increase from west to east late in the day Wednesday then all areas will have a chance for precipitation Wednesday night. There is a 30% chance of snow in the Wenatchee Valley during the day with a 50% chance of snow by Wednesday night, highs in the lower 30’s. Snow levels will be low enough that all precipitation will be as snow. Model guidance is showing a low end chance of freezing rain Wednesday night around Mattawa, Royal City, and Othello.

Through Wednesday night snow accumulations will be an inch or less for most of the lower elevations with 2-3 inches in the northeast Washington mountains and 3-6 inches near the crest of the Cascades. But this will just be the beginning as much more precipitation is expected Thursday and Friday.

The huge weather system really kicks into gear on Thursday with cloudy skies and an 80% chance of snow at first changing over to a rain/snow mix late in the day with highs Thursday in the mid 30’s.

Wet and warmer on Friday with an 80% chance of rain and afternoon high temperatures in the upper 30’s to lower 40’s. Hydro issues may creep up in the mix from about late Thursday night through Saturday night with rises on rivers such as the Stehekin in Chelan County. Mountain passes could pick up as much as 36 inches of snow over the next 3 days.

Rain is likely on Saturday too with highs remaining on the mild side near 40 degrees. Drier on Sunday and Monday with partly cloudy skies and highs in the mid to upper 30’s.