Avalanche Forecast

Snow levels will slowly lower Thursday night and lower further during the day on Friday. Showers, heaviest near the crest, should decrease overnight but then increase again by mid-day Friday as a low pressure system passes to our north. Snow showers may become locally heavy in the Washington Pass area Friday afternoon. W-SW transport 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 Washington Pass area in the afternoon. Storm slab sensitivity combined with the persistent W-SW transport winds may tip the scales toward High danger above treeline in the Washington Pass zone on Friday. 

For the southeast zone, be aware of the possibility of wet slabs even with the cooling trend. 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.   

Potential persistent slab layers should have received a good test during this avalanche cycle. We will wait for more information regarding PWL sensitivity and distribution in areas with a shallower snowpack and on isolated north facing aspects in the Washington Pass area before re-listing persistent slab.    

Weather and Snowpack

A strong storm cycle was seen Friday through Monday with 2-3 feet of snow reported along the Cascade east slopes on average with lesser amounts at lower elevations and in the Mission Ridge/Blewett area. A slow warming trend affected all areas Saturday afternoon. A nice day on Tuesday allowed for snowpack settlement and stabilization of the deep recent storm snow.

A strong plume of moisture brought heavy snow to the east slopes of the Cascades Wednesday night. A mix of snow, freezing rain, and rain was seen Thursday for the central and southeast Cascades while the northeast Cascades experienced a warming trend aloft but likely stayed mostly snow.  A strong cold front swept through the Cascades mid-day. Bands of light to moderate showers in SW flow followed the front. 

Precipitation totals through 4 pm Thursday: 

Recent Observations

North

A 5 cm layer of facets roughly 10 cm below the 1/17 crust may still be found in the Washington Pass zone and in areas further east. This reactive PWL has only been found in isolated locations in cold non-wind affected north facing terrain. No avalanche activity has been observed on this layer. 

Reports of gradually settling storm snow from the Washington Pass area are providing excellent conditions on mid angled terrain as of Tuesday. However The NCHG report a 1 m X 100 m natural slab avalanche on a run near Harts Pass known as Dogs Bowl that possibly released Monday or Monday night on a faceted layer below the recent storm snow. Details are lacking regarding aspect or elevation.

Central

No observations since Sunday.

South

A report via the NWAC Observation page for Umptanum Ridge for Tuesday indicates a shallow 70 cm snow pack with whumpfing due to buried surface hoar at 47 cm below the surface.