Mountain Weather Forecast

Weather Synopsis

The closed low over Northern California continues to wrap moisture around it and northward into the southern half of our forecast region. Mostly light but locally intense convective showers can be seen on the radar on Sunday afternoon, extending southward from the Mt Rainier area. This convection was spawned by gradual cooling aloft combined with divergent upper-level flow.  As the low pressure shifts further east Sunday night, westerly winds flow develops at all levels of the atmosphere over our region. Ridgeline winds ramp up into the moderate range for favored areas near and east of the Cascade Crest. The onshore winds contain enough low-level moisture (as seen by the plentiful low clouds offshore in satellite imagery) to maintain a steady supply of light rain and snow showers along the west slopes of the Cascades from the Canadian border to Mt Hood, with negligible spillover east of the Crest. Models hone in on weak convergence banding forming over the Snoqualmie Pass area Sunday night, which likely lifts northward towards Stevens Pass or the Mountain Loop as the pattern continues on Monday. Snow levels significantly lower from Sunday evening through mid-morning on Monday (from 6000 ft to around 4000-4500 ft, then stabilize). Middle and upper elevations can anticipate a few inches of snow.

A more significant winter-like storm system drops southward down the British Columbia Coastline Monday night, gradually shifting winds more SWerly and focusing the light shower activity more on the northern Cascades as snow levels lower to 3500 ft in the evening and around 3000 ft overnight. Moderate warm-frontal precipitation moves into the northern half of the forecast region on Tuesday morning, with lighter precipitation farther south. Moderate to locally heavy precipitation becomes widespread in the afternoon. This storm is favorable for snow above the 3000-3500 ft snow line. Expect a slight bump in snow levels as a subtle warm sector transits the area. Ridgeline winds increase into the moderate to strong range, peaking at the end of the day.