Avalanche Forecast
Regions: Cascades - East.
The avalanche danger will be increasing Wednesday. Fresh wind slabs should become sensitive and widespread. Cautious routefinding and conservative decision-making is essential. Evaluate the snow and terrain carefully and avoid steep terrain where wind deposited snow is evident.
Detailed Forecast
An approaching disturbance should bring renewed light to occasionally moderate snow at low snow levels with strong ridgetop winds overnight Tuesday and early Wednesday.
This should build new unstable wind slabs in exposed terrain, near and above treeline and some isolated features below treeline. Wind slabs should build on primarily on NW-NE-SEÂ facing slopes, but may build on a variety of terrain features.
Expect dangerous avalanche conditions Wednesday, especially at higher wind exposed elevations. Evaluate the snow and terrain carefully and change your mindset accordingly to more conservative choices.Â
Snowpack Discussion
Weather and Snowpack
The most recent warm and wet SW storm arrived on Valentines Day 2/14 and formed the uppermost strong rain crust in our snowpack in the Central-East and Southeast Cascades while only a thin freezing rain crust was observed in the Washington Pass area.Â
A slightly unstable weather pattern last week caused a mix of sun and light snow showers with sun crusts forming on solar aspects.
A period of increasing westerly ridgetop winds Saturday afternoon was noted at the Mission Ridge and Dirty Face Peak weather stations and by guides in the Washington Pass area.Â
Cool NW flow over the past several days has combined with weak disturbances to deposit varying amounts of low density new snow. Recent storm snow amounts vary from about 6-8 inches in the central and south to 14-18 inches in the north zone as of Tuesday evening, 2/28. Most of this snow has fallen at cold temperatures and with light winds, creating low cohesion surface snow.
Ridgetop winds increased Tuesday ahead of an approaching storm and thus beginning to build fresh wind slabs in exposed terrain. The cold low density surface snow will be very susceptible to wind transport with the arriving storm.Â
Recent Observations
North
Recent reports around the Washington Pass area and near Harts Pass over the past few days continue to indicate excellent quality snow conditions. The primary avalanche problem noted, were shallow wind slabs formed late Saturday in isolated areas above treeline due to moderate W-NW alpine winds.
A public observation received via the NWAC observation page Saturday indicated a small natural loose dry avalanche, possibly cornice triggered, that hit a skier on the Silver Star glacier.   Â
Central
No recent observations. Â
South
No recent observations.Â
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, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1