Mountain Weather Forecast

Weather Synopsis

Showers and the associated convective clouds have fired up over the mountains this afternoon thanks to the combination of a cold upper trough over the region and daytime heating. Scattered showers will drift from the SE to NW through early this evening and generally are more intense for areas near and south of I-90.  We'll see a mixed bag of cloud cover Tuesday night as showers wind down with a better chance of partial clearing west of the Cascade crest. Low-level easterly flow will lead to more cloud cover and a continued chance of light snow along the east slopes of the Cascades overnight.  We'll also see E-SE ridgeline winds tick up a notch into the moderate range for most areas. 

On Wednesday, we'll see a similar setup with a cold unstable air mass overhead and showers increasing in the afternoon. An upper-level feature extending from the upper trough offshore should help provide additional lift and lead to increased shower activity near the Mt Hood area in the morning and for the south Washington Cascades in the afternoon. With the increased offshore flow and easterly winds leading to downslope warming, look for the mildest temperatures and freezing levels west of the Cascade crest from I-90 to the Canadian border. Cloudier and cooler conditions will continue along the east slopes of the Cascades. More intense showers may contain graupel. 

On Thursday, a developing low pressure system will ramp up the offshore flow and E-SE wind during the day, with ridgeline winds becoming strong by Thursday afternoon. Warm frontal precipitation will approach the Washington and Oregon coast in the morning and may reach the Mt Hood area and south Washington Cascades with steadier light snow by the afternoon. Light upslope snows along the east slopes of the Cascades will likely increase during the day as well on Thursday.