Mountain Weather Forecast

Weather Synopsis

It feels almost tropical for the first day of December with mountain temps in the 40s and 50s and some 60s in the valleys and lowlands. The last in a series of atmospheric river events that have occurred over the last week will come to an end tonight as the frontal boundary finally shifts south from British Columbia towards the north Cascades, but loses its sub-tropical moisture tap in the process. The frontal boundary will hang up over the north/central Cascades with snow levels slowly lowering to 4500-6000' Wednesday night.  A few inches of snow may accumulate above these levels, particularly in the Mt Baker area down to the Mtn Loop highway through Thursday morning. While leftover showers will decrease along the west slopes of the Cascades during the day Thursday, low-level clouds will stick around for the central Cascades.  Other areas will be dry, but with periods of high clouds.  The strong westerly ridgeline winds and extreme alpine winds experienced in many areas since Tuesday will slowly start to decrease Wednesday into Thursday. 

The jet-stream positioning will largely stay unchanged through Friday over southern British Columbia with zonal westerly flow aloft. The relative cooling that does occur Wednesday night will struggle to push south and the result will be an exaggerated N-S freezing level gradient with the warmest freezing levels down near Mt Hood through the short term.  A developing frontal system offshore will merge with a broad upper trough swinging south from the Gulf of Alaska later Friday. While Friday will be a dry day overall, high and mid clouds will stream over the area and there is a chance that some precipitation will work its way into the central/northwest Cascades by Friday afternoon.