Avalanche Forecast

On Friday, a frontal system should stall over the Olympics and north Cascades before finally sagging south in the late afternoon and evening. Alpine winds generally out of the SW will increase late Thursday night and stay elevated through Friday. New and generally shallow storm snow instabilities may develop in the Mt. Baker zone on Friday. However, fresh wind slab may build at higher elevations in all zones during the day. 

Wind slab is the most likely avalanche problem to encounter on Friday, with deeper and potentially more sensitive slabs possible in the Mt. Baker area. Use caution and watch for firmer wind-transported snow on lee slopes near ridges, generally northwest through southeast aspects, but expect wind deposited snow on a variety of aspects in areas of more complex terrain.

Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.

The great start to the 2017/18 PNW Winter lasted through mid November. Warm, wet weather before Thanksgiving caused wet snow and glide avalanches and snowpack consolidation with total snow depths decreasing by 50% or more from their mid-November peak depths. The old wet snow continues to slowly refreeze and from a crust of variable strength along the west slopes of the Cascades including the Passes.

A series of fast moving frontal systems have brought several inches of snow to the west slopes of the Cascades this week. Mt. Baker has received the most snow since Monday, about 2 feet. 

This graph shows new snowfall received at 5 different NWAC stations during the week. 24 hr snowboards are manually cleared by ski areas/DOT operations each morning. 

Observations

North

On Thursday, Mt. Baker pro-patrol triggered isolated pockets of wind slab about 20 cm (8") deep during control work.  Also on Thursday, guides in the Mt. Baker area reported about 85 cm of recent storm snow above the Thanksgiving crust bonding well to the crust and within recent storm layers. However, active wind loading was occurring on north facing aspects around 5000'. 

Central

Wednesday in the Alpental backcountry, NWAC observer Ian Nicholson found areas of unreactive wind slab on some east facing terrain features near ridges. Daytime solar warming had allowed surface snow to consolidate and form shallow storm slabs, but no avalanches were observed or triggered. 

South

On Thursday in the Crystal backcountry, NWAC pro-observer Dallas Glass found 25 cm (10") of this week's storm snow bonding well to the stout and fully supportable Thanksgiving rain crust. Shallow wind slab averaging 10-15 cm (4-6 cm) thick was found below ridges on W-N-E aspects, but was isolated in distribution. Total snow depth in this area peaked at about 1 meter at 6000' and above.