Avalanche Forecast
Regions: Cascades - East.
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 with more conservative travel plans than you might otherwise given the same danger rating.
Detailed 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.Â
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. Â Â
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.Â
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.  Â
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.   Â
Snowpack Discussion
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.Â
Precipitation totals through 4 pm Thursday:Â
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.Â
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.
Avalanche Problems
Wind Slabs
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East, South.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1