Mountain Weather Forecast

Weather Synopsis for Wednesday & Monday

A deep trough offfshore of the Alaskan panhandle is moving south Wednesday as it combines with several closed low circulations off the California coast which are currently impacting California with plentiful moisture. The combined trough and associated developing S-SW flow aloft over our region will tap into some of this moisture and mild air and will bringing it over the forecast area, particularly overnight and Thursday morning ahead of a surface frontal feature currently aligned SW-NE offshore that will swing toward the coast. 

On Wednesday afternoon, bands of light to briefly moderate showers are moving north across the South Cascades and Hood and will arrive in the central Cascades by late afternoon. Rain and snow shower activity will increase overnight and Thursday morning ahead of the front as it approaches.  Snow levels will peak during the morning hours on Thursday, changing snow to rain at the Mt. Baker base during the morning areas and for a few hours at Washington Pass during the mid-day hours before cooling by 2PM changes most locations above pass level back to snow. The cooling is associated with the sharp cold front, which reaches our forecast area oriented N-S, arriving on the Oregon coast Thursday morning around 8 AM, Hood and the Olympics by 11 AM and it should pass through the Washington Cascades by around 2PM. Precipitation will decrease behind the front on Thursday afternoon. The frontal passage will coincide with a period of elevated wind speeds in the moderate to occasional strong range at Crest level. It will also be associated with a shift from easterly to westerly flow in the passes, although the overall flow will only re-orient slightly from S-SW to SW.

Thursday and Thursday night the upper trough will spin about a stationary low pressure centered SW of the Queen Charlotte Islands.

Thursday night the flow aloft will once again become more southerly with a SE wind component at lower levels. Snow showers will increase in some areas Thursday night as a band of energy associated with the broad upper trough moves over the region, temporarily increasing wind speeds.

In general, the Cascade volcanoes will receive the most moisture from this system, followed by the east slopes of the Cascades the Cascade passes will receive less moisture.