Avalanche Forecast
Issued: Dec 11th, 2019 10:15AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs.
NWAC,
Northwest Avalanche Center
A potent winter storm will bring heavy snowfall and strong southerly winds Wednesday night and Thursday. Expect dangerous avalanche conditions near and above treeline. Give the storm snow time to stabilize, and seek out low-angle, supported terrain away from overhead hazard.
Summary
Discussion
So far this season, avalanche activity has been minor and infrequent due to low snow. Over the next 24 hours, this storm will bring rapid change. Slab avalanches may become easily triggered and widespread on upper elevation slopes. Snow levels will be near 3500ft, and 2ft+ of new snow is expected above 4500ft by late afternoon Thursday. Avalanche danger, along with snow totals, will increase sharply as you gain elevation.
Don’t let the excitement of this first major winter storm distract you from making informed and conservative decisions. Be very cautious if you decide to venture out during the storm. Ease into terrain slowly and gather information along the way. Getting caught in even a small avalanche would be a rough ride with high consequences in these early season conditions. Expect to encounter shallowly buried objects and challenging travel conditions.
The few inches of new snow that we received in the past 24 hours has already formed shallow slabs reactive to skier traffic. Northwest aspect at 5500ft near Bearpaw/Church Lake in the Hwy 542 Corridor. 12/11/19. Photo: Pete Durr.
Snowpack Discussion
Regional Synopsis Coming Thursday, December 12, 2019
Problems
Storm Slabs
Heavy snowfall will build fresh storm slabs over the next 24 hours. Large natural and human triggered avalanches are most likely where new snow falls on upper elevation slopes with pre-existing snow cover. Wind-loaded terrain will develop thicker and more reactive slabs. The new snow is not expected to bond well to firm and variable old snow surfaces, and mid-storm layers may be reactive as well. Watch for shooting cracks, collapses, and recent avalanches, and avoid avalanche terrain at upper elevations during periods of intense precipitation.
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: Dec 12th, 2019 10:15AM
