Mountain Weather Forecast

Weather Synopsis

A strong upper and surface low stationed off the northern California Coastline  has cut off from the jetstream, leaving our region under split flow on Tuesday afternoon. A weak high over southern British Columbia influences the regional weather through Wednesday morning, leaving most areas under clear skies. However, some slight influence from the California low has produced some weak instability as far north as Yakima on Tuesday afternoon. Light ENE winds are taking isolated convective cells toward the Cascades. These cells should dissipate overnight without the influence of the sun's surface heating and as the California low continues to drift southward. E and NE winds across the region should remain light through mid-morning on Wednesday. However, these winds may remain in the moderate range through Tuesday night in the Mt. Hood area, driven by a slightly stronger pressure gradient across the Oregon Cascades. Although most areas will be mild overnight, expect slightly cooler temperatures E of the Cascades, through the mountain gaps, and in deep valley locations where cold air pools.

Temperatures warm during the day on Wednesday, but expect increasing clouds in the afternoon and a shift to W winds as a weak shortwave trough approaches. Some light rain and snow develops late in the day for the Olympics, Southern Washington Cascades, and Mt. Hood in the afternoon.

Mostly light rain and snow focus on the west slopes of the Cascades with very light spillover Wednesday night. There exists a possibility for locally moderate precipitation at times for the southern Volcanoes and in a convergence band aimed NE from the Olympic Mountains. Snow levels should be around 3500-4500 ft. Winds shift gradually to the SW ahead of a cold upper low dropping down the coastline from the Gulf of Alaska.

Thursday's system comes with a strong upper-level cooling trend and snow levels lowering to around 2000-2500 ft. A front passes through the region on Thursday at the leading edge of the upper low. Expect moderate SSW winds in advance of the front (strongest at Mt. Baker) along with light to moderate rain/snow showers and convergence. Winds shift W behind the front focusing post-frontal showers.