Avalanche Forecast
Regions: Olympics.
Avalanche danger will increase slightly on Thursday as shallow wind slabs may develop on wind-loaded aspects if sufficient snow accumulates. Continue to use normal safe travel practices and avoid slopes with signs of active or recent wind-loading, including blowing snow or shallow pillows of wind-stiffened snow and avoid such terrain steeper than 35 degrees.
Detailed Forecast
Shallow wind slabs may develop as 1-4" of new snow accumulates Wednesday night through the day on Thursday above 4,000 ft. Moderate to occasionally strong SE through SW winds at ridge-top will transport that snow onto a variety of aspects. Temperatures will drop sharply during the day.
The shallow wind slabs are unlikely to cause a major travel hazard given the anticipated snowfall amounts. Normal precaution in potentially wind-loaded terrain near and above treeline includes watching for active snow transport, plumes of snow, snow pillows with firmer snow, or crusts exposed on ridge-tops. If such conditions are encountered, avoid steeper terrain.
The new snow should bond well to crusts on non-polar aspects due to the relatively warm temperatures.Â
Polar aspects should have mostly dry snow with some thin, unsupportable crusts present.Â
Expect the potential for variable snow surfaces including firm crusts, breakable crusts, and various states of shallow powder.
Cornices are an ongoing hazard in the terrain and if one fails it will entrain up to 6" or more of lower density snow on shaded aspects.Â
Snowpack Discussion
Several days of sunny, spring-like weather should have created a crust on non-polar aspects.
About 2 inches of new snow was reported Monday morning by NPS rangers and sits on a strong crust formed after 4.5" of snow fell late Friday on another strong and supportable crust.
On shaded slopes, a thinner melt-freeze crust formed last weekend. This crust is likely semi-supportable and may be covered by 4-6†of soft snow in some places. Soft snow will be most prevalent on shaded slopes at higher elevations.
Several layers exist within the snowpack. Currently we do not have any information suggesting that any of these layers are a potential problem.
Observations
NPS Rangers, reported 2" of new snow over a strong crust Monday morning.
NPS Rangers, reported 4.5" of new low density snow with no wind effects over a very strong crust Sunday morning.
NPS Rangers found a well settled snowpack on NE aspects around 5500' Thursday 3/15. They did not identify any layers of concern in the upper snowpack. No new or recent avalanches were observed.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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1