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Archived

Avalanche Forecast

Dec 2nd, 2017–Dec 3rd, 2017
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Cascades - South West.

Avoid avalanche terrain in the Mt. Baker Area until new storm slabs stabilize. 

Elsewhere watch for sensitive wind slabs on Saturday. Approach ridges cautiously and watch for firmer wind-transported snow. Storm slabs should be less reactive than Friday, but will still be possible to trigger in steeper terrain. Take a more conservative approach Saturday to enjoy the new snow safely.

Detailed Forecast

Generally light and scattered showers Saturday morning should transition to more widespread shower activity in the afternoon. See the NWAC mountain weather forecast tab for more details. 

Mt. Baker received the heaviest new snow by Saturday morning with approximately 20 inches. It will be best to avoid avalanche terrain in the Mt. Baker Area until this new snow stabilizes. 

Throughout the west slopes, expect sensitive wind slabs on Saturday.  Approach ridges cautiously and watch for firmer wind-transported snow. Storm slabs should be less reactive than Friday, but will still be possible to trigger in steeper terrain. Take a more conservative approach Saturday to enjoy the new snow safely.  

Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.

Snowpack Discussion

Warm, wet weather before Thanksgiving caused wet snow and glide avalanches as well as significant snowpack consolidation. There are no snowpack concerns below the Thanksgiving crust and in general new snow received post-Thanksgiving has reportedly bonded well throughout the range. 

During the week, a series of frontal systems have generally produced light amounts of the new snow for the west slopes of the Cascades. The exception is in the Mt. Baker area who received about 3 feet of snow this week including roughly a foot during the day on Friday. No significant avalanche activity has been observed outside of the Mt. Baker zone. 

Observations

North

Update: On Saturday morning, the Mt. Baker Ski Area reports widespread 10-14" touchy ski-triggered storm slab on all aspects along with a couple similarly sized natural avalanches. 

Central

Wednesday in the Alpental backcountry, NWAC observer Ian Nicholson found areas of unreactive wind slab on some east facing terrain features near ridges. Daytime solar warming had allowed surface snow to consolidate and form shallow storm slabs, but no avalanches were observed or triggered. 

On Thursday, NWAC observer Jeff Ward found about 40 cm of settled snow well bonded to the Thanksgiving Day crust in the Stevens Pass backcountry. With good visibility, no avalanche activity was noted in the surrounding terrain.  

South

On Thursday in the Crystal backcountry, NWAC pro-observer Dallas Glass found 25 cm (10") of this week's storm snow bonding well to the stout and fully supportable Thanksgiving rain crust. Shallow wind slab averaging 10-15 cm (4-6 cm) thick was found below ridges on W-N-E aspects, but was isolated in distribution. Total snow depth in this area peaked at about 1 meter at 6000' and above.  NWAC pro-observer Jeremy Allyn found similar conditions on Friday and noted the lack of cornice formation along ridges. 

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: Possible

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