Avalanche Forecast

A period of moderate rain and snow at rising freezing levels is expected Wednesday night along with strong S-SW  ridgetop winds. Showers should taper quickly Thursday morning. A modest cooling trend is expected by early Thursday, however, the new storm related danger will continue through Thursday due to strong southwest winds loading lee slopes during showers Wednesday night. 

Storm slab instabilities should be stabilizing, but may still be sensitive Thursday. Wind slabs will continue to build Wednesday night on lee slopes, facing generally NW-NE.  Earlier formed wind slabs may still be reactive Thursday and may add to the increasingly complex snow structure, by Thursday.

Conservative terrain selection will be essential near and above treeline to avoid wind loaded terrain and features. Choose moderately angled terrain and avoid wind loaded slopes, saving those steeper lines for another day.

Non-avalanche hazard: Despite our seasonally healthy snowpack, many creeks are open and difficult to cross due to the periodic warm temperatures and rain events.  

Weather and Snowpack

Very mild weather a week ago allowed for the formation of a strong melt-freeze crust, especially thick on solar slopes in most areas by Friday.

A Pacific frontal system blew through the Cascades mid-day Sunday. The most significant transport winds were from the W-SW and seen early Sunday afternoon with gusts in the 40s or 50s below or near treeline with much stronger winds above treeline. By Monday morning, 4-12 inches of new snow had accumulated along the west slopes accompanied by a cooling trend. 

A warm front quickly dropped up to 10 inches of new snow early Tuesday morning at NWAC stations before snow either eased off mid-morning or changed to rain outside the Cascade Passes. Precipitation rates increased again in the afternoon as the cold front approached. In the Mt. Baker area, precipitation rates increased later in the morning with the snow level rising above 5000 ft during the day. This caused a natural avalanche cycle late Tuesday in many areas, evidenced by many field observers Wednesday morning.

Additional precipitation late Tuesday through Wednesday morning with cooling deposited an additional 6-15 inches of snow. Surface snow layers are a mix of varying density dry or moist snow all well bonded to a forming rain crust or old moist to wet snow.   

The mid and lower snow pack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

NWAC observer Tom Curtis was out on Jove Peak Monday. Jove Peak is NE of Stevens Pass and often overlaps snowpack characteristics of both the east and west slopes of the Cascades. Tom noted few instabilities in the upper snowpack until he observed a large natural wind slab avalanche (R2-D2) on the north side of Jove Peak that probably released Sunday night. The wind slab was 40 cm in depth and stepped down to a 2 mm buried surface hoar layer at 50 cm. The buried surface hoar was rounding, but clearly still sensitive to new loading. 

A stormy day on Tuesday limited observations, but one observation submitted via the NWAC observation page from behind Windy Ridge near Stevens Pass reported increasing instability and sensitivity to triggering with a large soft slab avalanche on a WNW aspect running well and entraining moist snow lower in the path. 

By Wednesday sunshine and daytime warming caused numerous natural point release, Loose-Wet avalanches on steep solar aspects seen in the Alpental Valley and the Mt Baker backcountry.

Control work at Alpental produced widespread wind slab releases in the upper elevations where wind transport was more significant.