Mountain Weather Forecast

Weather Synopsis

The parade of fronts on a moist SSW flow continues with the main event arriving Tuesday through Wednesday morning.

Monday evening light snow showers decrease across the northern Cascades. Attention shifts to the southern Cascades where a weak warm front lifting northward brings moderate rain and snow to the southern Cascade Volcanoes with moderate E flow enabling plenty of spillover onto the east slopes of the Cascades. The front peters out once it reaches the central Washington Cascades overnight.

An atmospheric river arrives with a warm front moving into the area on Tuesday. This will bring light precipitation with snow levels around 3000-4000 ft west of the Cascades and at valley bottoms east of the Cascades and through the mountain gaps. As the day progresses, precipitation becomes moderate to heavy throughout the central and southern Cascades, and particularly the Olympics. The precipitation also reaches the northern Cascades in the afternoon. SSW flow will bring significant warming, initially to the Olympics and southern Cascades during the afternoon hours with snow levels rising to near the Cascade Crest in these areas late in the day. The timing of the warmup remains an area of significant uncertainty.

Moderate to heavy rain, snow, and freezing rain continue as warm air rides over the cold air entrenched east of the Cascades and through the mountain gaps. Expect around 50% of the precipitation falling around Snoqualmie Pass, Stevens Pass, and areas further east to be in the form of freezing rain Tuesday night. That means rain will fall in a layer above these freezing temperatures.

A cold front moves through Wednesday morning, shifting winds from SSW to W and bringing an end to the steady precipitation. Temperatures gradually cool with snow levels lowering to 3500-5500 ft in the afternoon after topping out around 7500 ft Tuesday night.