Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain on Saturday
Weather Forecast
A surface ridge moves into the region Friday keeping the area dry while northwesterly flow aloft keeps scattered clouds in place. Ridgetop winds will be at strong values out of the W near ridgetop Friday & temps will remain cool; Expect a daytime High of -5 and an overnight Low of -12 @ 1500 m. Things begin to change a bit Saturday as the ridge breaks down allowing moist flow in from the pacific. The first storm associated with the new pattern enters the region Saturday night, sticking around through Sunday. Freezing levels are expected to rise to 1300 m Saturday night and storm totals from 20 - 40 cm are forecast at this time.
Avalanche Summary
A widespread natural avalanche cycle occurred yesterday on all aspects at and above treeline. There were several avalanches to size 2 and a few to size 2.5 & 3 on all aspects.
Snowpack Summary
An additional 20 - 40 cm of new snow from Tues & Weds sits just above the weekend's 30 - 70 cm, making for a meter plus of storm snow. Shears within the new snow have been short lived. The big story is the wind; winds associated with the Tues/Weds storm were strong gusting to extreme out of the W & SW. These winds left widespread wind damage at all elevation bands & set the stage for a large and widespread avalanche cycle Wednesday that produced several avalanches to size 3 with crown depths near 100 cm. These winds also created large cornices in the region which much be treated with respect.Many folks have been concerned about the January 20th facets that were created with the outbreak of Arctic air. We often think of super cold temperatures as driving faceting, and that's right, but the faceting mechanism actually occurs much slower at very cold temperatures like the ones we experienced last week. There's been limited activity down at this interface suggesting that problems associated with this layer will be short lived.This load has also been a good test for the January 13th SH/FC layer which is now buried 110 - 150 cm in depth. It hasn't produced much activity either. Its distribution is spotty though, and backcountry users need to factor this layer into their thinking for the weekend, especially in areas where the snowpack is thin.A surface hoar layer buried in mid-December is gaining strength, but professionals are still treating it with caution as the consequences of an avalanche on this layer would be high. Occasional hard, planar results have been reported on this layer in snowpack tests. It's now down about 200cm in the snowpack.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.