Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 12th, 2015–Dec 13th, 2015

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Stevens Pass.

The strong storm Saturday should have created widespread new storm layers and new unstable wind slab on lee slopes near ridges by Sunday with further snowfall and winds expected during the day Sunday. Travel conservatively by staying off or below steeper slopes and avoid wind loaded north and east facing terrain.

Detailed Forecast

Snow showers will continue Sunday with moderate ridge top winds. Temperatures should remain cool.

Recent storm and wind slabs may continue to build and storm layers from Saturday and Saturday night will not have settled or stabilized by Sunday. 

Either wind or storm slabs should remain sensitive and likely to trigger. North to east facing lee slopes will continue to be loaded throughout the day as well.  

Dangerous avalanche conditions are expected near and above treeline requiring conservative decision-making and cautious routefinding.

Travel conservatively by staying off, or below steeper slopes and avoiding the wind loaded terrain near and above treeline.

Be aware of early season hazards below treeline. The heavy rains from last week have left many creeks open at lower elevations. 

Snowpack Discussion

Snowfall over the west slopes the first week of December ranged from 1-4 feet. An atmospheric river arrived early in the week and heavy rain fell over the west slopes, with water amounts ranging from about 5 to 8.5 inches in just 2 days ending Wednesday morning!  Since Wednesday, 10-20 inches of new snow has fallen along the west slopes through Saturday afternoon. 

Avalanche and Snowpack Observations

The warming and rain or heavy wet snowfall a week ago did cause avalanches and some very close calls with slides releasing on persistent weak layers above the mid-November crust. 

The now positive effect of all that rain earlier this week was to really stress the snowpack, removing lingering problem layers. Persistent weak layers in the Stevens and Snoqualmie zones should have been eliminated and as a result, the persistent slab problem has been removed from the forecast problems.  

Reports Friday by NWAC observers in the Stevens Pass and Baker backcountry reported no natural or skier triggered avalanches within the new snow with a generally right-side up layered upper snowpack near and below treeline and a favorable bond to the newly formed crust. Crystal patrol reported significant loading from the SE winds near and above treeline Thursday, but little instability in the way of control results Friday AM. 

Reports coming through the Crystal patrol Saturday afternoon from backcountry skiers returning from the Crystal south backcountry, indicated increasingly sensitive triggered soft slab releases up to 8 inches within the new storm snow. No specifics were reported. 

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.