Avalanche Forecast
Issued: Feb 2nd, 2016 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Storm Slabs.
NWAC,
Northwest Avalanche Center
Expect increasing avalanche danger Wednesday afternoon and evening with shallow new storm and wind slabs developing. Change your travel plans if storm hazards deteriorate more quickly than forecast.
Summary
Detailed Forecast
New and shallow storm and wind slab should begin building Wednesday afternoon and evening as a Pacific frontal system approaches from the west.
New snow may initially bond poorly to a variety of snow surfaces Wednesday with a thin sun crust on solar aspects and low density snow and/or surface hoar on shaded and non-wind affected terrain.
Change your travel plans if storm hazards deteriorate more quickly than forecast.
Additional snowfall and wind loading Wednesday night will increase the storm related avalanche hazard on Thursday.
Snowpack Discussion
Weather and Snowpack
Two fair weather periods earlier this month allowed surface hoar and near surface faceting to occur. These persistent weak layers were buried intact on January 3rd and 11th throughout the Cascades. Two heavy rain events, one about January 21st and another January 27-28th have eliminated the January persistent weak layers and formed crusts in the upper snowpack along the west slope zones.
A strong occluded front with strong winds crossed the Northwest on Friday. NWAC stations along the west slopes had about 1-1.5 feet of new snow by Saturday morning. Light amounts of snow followed at the tail end of the storm by Sunday morning. The most recent snowfall fell on top of the rain crust from late last week. Cool and benign weather followed Sunday through Tuesday. Varying amounts of sunshine Tuesday along the west slopes likely formed a sun crust on steeper solar aspects.
Recent Observations
Three NWAC pro-observers visited the Stevens Pass and Paradise areas on Sunday and generally reported possible wind slab on previous lee slopes and possible storm slab in storm snow in the near and above treeline as the main avalanche problems.
NWAC pro-observer Lee Lazzara was in the Mt Baker area on Monday and reported small wind slab varying in depth from 20-40 cm over slightly lower density snow but lacking clean shears. Skiers were also triggering loose dry avalanches on steep 45 degree slopes. Lee reported similar conditions in the Baker backcountry on Tuesday with the rain crust 50-80 cm down.
Pro-observers Ian and Dallas were on Snoqualmie Mt Tuesday and generally found low density snowfall above the most recent rain crust providing good skiing conditions with minimal wind effects. The most recent snowfall was not cohesive enough to form a storm slab in their specific area.
NWAC observer Jeff Ward was in the Stevens Pass area Tuesday. He generally found a stable upper snowpack, but observed new surface hoar growth most prominent in Highland Bowl near ridgecrest.
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
Expected Size
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
Expected Size
Valid until: Feb 3rd, 2016 10:00AM
