Avalanche Forecast

What a difference a day makes as we quickly transition from mild and wet to cool and showery weather on Friday. Snow levels will slowly lower Thursday night and lower further during the day on Friday. Showers should decrease overnight but then increase again by mid-day Friday as a low pressure system passes to our north. Snow showers may become especially heavy in the Mt. Baker area Friday afternoon. W-SW winds will be moderate to occasionally strong Thursday night and Friday. 

After a period of wild weather Wednesday night and Thursday that closed major highways and limited observations, there is a higher than normal amount of uncertainty about the snowpack heading into Friday. Account for the uncertainty by choosing more conservative travel plans than you might otherwise given the same danger rating.

Moderate to occasionally strong W-SW winds will transport new and recent snow onto lee slopes near and above treeline. Wind slab may build down into the below treeline band on Friday. Easterly aspects will be identified in the elevation/aspect diagram but watch for firmer wind transported snow on a variety of aspects.   

Despite the cooling trend, new storm slab instabilities may develop during periods of intense showers. Storm slab instabilities are likely to develop in the Mt. Baker area in the afternoon.  

For areas west of the Cascade crest including Mt. Baker, Crystal and Mt. Rainier, wet slabs will be listed as unlikely due to the cooling trend. However, avoid travel below unsupported slopes, especially near and below treeline, with the low likelihood/high consequence of large wet slab avalanches in mind. Wet slab releases are hard to predict and can happen a day or two after peak warming and rainfall.   

Weather and Snowpack

A strong storm cycle was seen Friday through Monday with about 3-5 feet of snow recorded along the Cascade west slopes. A period of brief warming on Saturday created a weak crust layer that has now been found both at Stevens and Snoqualmie down at least 3 feet. 

A strong plume of moisture brought heavy rain to the west slopes of the Cascades (Mt. Baker, Crystal and Paradise) Wednesday evening through Thursday with a mix of snow, freezing rain, and rain seen in the Cascade Passes. A strong cold front swept through the Cascades mid-day. Bands of light to moderate showers in SW flow followed the front. A switch to westerly flow brought a bump up in temperatures in the Cascade Passes Thursday afternoon while areas further west were already beginning a slow cooling trend.  

Precipitation totals through 4 pm Thursday: 

Recent Observations

North

No observations Thursday. 

Central

NWAC pro-observer Jeremy Allyn was in the Henry Creek drainage below Jim Hill on Wednesday and reported that wind transport was underway due to the incoming storm. Quick tests of the near surface snow did not show significant results and ECT and PST tests on the 2/4 interface at 75 cm down did not indicate propagation. NWAC pro-observers Jeff Ward at Skyline at Stevens and Ian Nicholson near Alpental on Wednesday did find significant signs of instability.

Stevens Pass pro-patrol and DOT reported a natural avalanche cycle Thursday morning with major paths running D2 - D3. The pro patrol also observed some natural activity off Skyline Ridge and heard an unusual report of a path running to the Nordic road in Mill Valley.

On Thursday, Alpental pro-patrol reported a breakable freezing rain crust (i.e. less stout than the 1/17 IFrc) that made for tough ski conditions. Cornices along ridgelines weakened during the warming with some cornice breaks observed in the early afternoon. The cornice failures triggered some D1-D2 storm slabs below ridges and occurred post freezing rain as there was not an ice coating on the debris.  

South

Crystal patrol observed several loose wet slides up to size D2, all aspects, within the ski area Thursday. No large slab releases were produced with explosives Thursday afternoon. Wet slabs estimated to be about 1 ft deep were observed from the ski area in Pickhandle Basin.