Forecast snowfall amounts are highly variable throughout the region with the south expecting the highest accumulations. If overnight snowfall amounts are greater than 20cm, the actual avalanche danger may be higher than posted.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Overview: A series of disturbances are embedded in a west/southwesterly flow which will bring continued snowfall to the region. There is some model disagreement in the track of the systems; however, southern parts of the interior are generally expected to see the highest accumulations.Monday night: Up to 20cm of snow / Strong southwest winds / Freezing level at surfaceTuesday: Light snowfall / Moderate to strong westerly winds / Freezing level at about 700mWednesday: Up to 20cm of snow / Moderate southwest winds / Freezing level at about 1100mThursday: Light flurries / Moderate to strong southwest winds / Freezing level at about 1100m
Avalanche Summary
In the Dogtooth Range on Friday, skiers initiated a cornice fall which triggered a size 2.5 slab avalanche on the slope below. In the same area on Saturday a size 2 slab was rider triggered from a ridge crest. A size 2 natural slab avalanche was observed on Saturday further south in the region. The February 10th interface is thought to have been the culprit in all of these events.I would expect fairly widespread storm slab avalanche activity with ongoing snowfall and wind.
Snowpack Summary
In some areas over 40cm of new snow is expected to overlie weak surface hoar in sheltered areas, a sun crust on solar aspects and thin wind slabs in exposed terrain. Initially, these new accumulations are expected to react as a wind slab in exposed terrain. As the new slab deepens and gains cohesion by wind and warming, more widespread storm slab activity can be anticipated.There is ongoing concern for a mix of weak surfaces which were buried on February 10th. This persistent interface lies between 50 and 120cm below the surface, and includes surface hoar, well developed facets and a mix of hard surfaces which remain widespread at all aspects and elevations. Although natural avalanche activity has tapered-off at this interface, destructive avalanches are still a very real concern with ongoing reports of human triggering, whumpfing and sudden/easy snowpack test results. The mid and lower snowpack are generally strong and well consolidated. Weak basal facets exist in many areas, but triggering has now become unlikely.
Problems
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.