Mountain Weather Forecast

Weather disturbances moving into the west coast from the eastern Pacific are running into a full latitude split in the westerlies with a large area of very weak upper level flow extending from the Yukon to Baja. This split is significantly weakening, slowing and stretching incoming weather systems, with any weakened storm remants that actually reach the Northwest moving with sloth-like speed across the area. With very little wind to mix the atmosphere and move recent lower and mid level moisture out of the area and a weak upper trough only slowly exiting the area into southeast WA early Monday morning, only very slowly decreasing clouds occurred in most areas Monday morning, mainly along the Cascade west slopes, with a weak east to southeasterly flow helping to lift lingering moisture and maintain mostly cloudy skies east of the Cascade crest mid-day. 

The next incoming weather system currently about 120 miles offshore should significantly stretch and split during the afternoon as it encounters the strongly difluent flow over the region, with most of its energy and the associated upper low expected to head mostly south into California overnight into Tuesday. This should leave the NW under the influence of a very weak split ridge for the rest of Monday, with a very slow decrease in clouds expected mid-day and Monday afternoon as the surface and upper level flow gradually turn weakly east to southeasterly and daytime heating helps develop some cumulus and scattered flurries.

However, by late Monday some return flow circulation around the southward sinking upper low offshore should spread some increase in clouds and light showers northward into the Mt Hood area and southern WA Cascades overnight into early Tuesday. As the low sinks further southward, the clouds and showers should retreat southward with it, producing generally decreasing clouds and some sun breaks on Tuesday in a continuing weak split ridge over the region. The very weak northern part of the sheared CA low should move across southern BC and extreme northern WA late Tuesday. This should produce little more than some increase in clouds and a chance of light showers, mainly in the north Tuesday night.