Regions
Northwest Inland.
The March 09 persistent weakness is very sensitive to human triggering and is producing frighteningly large avalanches. Stay conservative in your approach to the mountains this weekend.
Confidence
Poor - Due to limited field observations
Weather Forecast
Synopsis: The pattern over the next five days starts out cool, convective and gusty. It will gradually turn milder, more stable and less windy towards SaturdayFriday: Freezing Level: Valley Bottom. Precip: No significant precip expected. Wind: Light, North.Saturday: Freezing Level: 600m Precip: No significant precip expected. Wind: Light, NWSunday: Freezing Level: 600m Precip: No significant precip expected. Wind: Light, South
Avalanche Summary
Wednesday's storm kicked off a natural cycle to size 3. Skiers are remote triggering large destructive avalanches (size 2.5) from as far as 800m away. This adds to the numerous avalanches that are reported to have failed on this layer over the last few days. I expect the trend to continue through the weekend.
Snowpack Summary
The region picked up 15 - 25 cm of new snow out Wednesdays storm which adds to the 20-40 cm snow that the region has received over the last few days. This 35 - 65 cm of recent snow rests on a variety of old snow surfaces, including crusts, previous wind slabs and surface hoar (buried March 9th). Warmer temperatures and recent winds have now set this new snow into a reactive slab. The March 9th surface hoar layer is reported to be very touchy and appears to exist at all elevations and aspects. It seams to be most electric on south through west facing slopes. I suspect cornices have become well-developed and could easily become unstable on slopes receiving direct sun. The mid snowpack is generally well settled and strong.
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.
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.