Avalanche Forecast
Issued: Jan 31st, 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
The greatest avalanche problem should be wind slab on lee slopes near and above treeline mainly NW-N-SE facing slopes. Watch for signs of firmer wind transported snow.
Summary
Detailed Forecast
Light winds, cloudy weather, a few light snow showers and cool temperatures should be seen along the west slopes on Monday.
This weather should bring a further gradually decreasing avalanche danger on Monday.
The greatest avalanche problem should be wind slab on lee slopes near and above treeline mainly NW-N-SE facing slopes. Watch for signs of firmer wind transported snow.
Watch for storm slab in areas that had rapidly accumulating snowfall. Storm layers that may exist above the new crust will slowly settle but could remain reactive to human triggers mainly near and above treeline.
Continue to evaluate snow and terrain carefully on Monday.
Avoid ridges where cornices may be present and slopes below cornices. Cornices can always be sensitive to human triggers.
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.
Two heavy rain events, one about January 21st and one last Wednesday-Thursday have likely eliminated the January persistent weak layers and they have been removed as an avalanche problem from 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. Some further light amounts of snow except for about 7 inches at Mt Baker followed at the tail end by Sunday morning
Some areas have reported a strong bond of the new snow to the new crust and some a poor bond depending on if the new snow arrived after cooling began. There have also been sensitive storm layers reported within the new snow which will take a bit of time to gradually stabilize.
Recent Observations
NWAC pro-observer Simon Trautman ventured into the white out in the Mt Baker back country Friday afternoon. New sensitive wind slabs were quickly forming on a variety of exposed aspects near treeline during heavy snowfall and very strong westerly winds. Drifts were 8-18 inches and increasing. There was an intact layer of low density stellar crystals just above the crust forming the weak layer and reactive to skis on wind loaded terrain.
New sensitive wind slabs forming in the Mt Baker back country Friday afternoon January 29th. Photo by Simon Trautman.
The Crystal pro-patrol on Saturday reported isolated 6-8 storm slab via ski cuts on varied aspects. The Alpental pro-patrol reported no significant avalanches and that new snow was not cohesive.
NWAC pro-observer Dallas Glass was at Paradise on Saturday and noted wind transport near and above treeline, a poor bond of the new snow to the new crust and some consistent weak storm layers via shovel tilt tests.
A couple of observations are available via the NWAC Observations page. A skier triggered a 7-10 inch wind slab at Stevens Pass on a lee northeast slope Saturday. Generally stable conditions were seen at Stevens on a trip to Lake Valhalla.
Less activity is reported so far today. The Crystal Mountain pro-patrol reported a lack of wind, some unconsolidated snow and no avalanches.
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 1st, 2016 10:00AM
