Regions
Northwest Inland.
Confidence
Poor - Due to limited field observations
Weather Forecast
Synopsis: A strong low pressure system today with wind and mild temperatures is followed by a cool and unsettled air mass through Friday. Conditions will become gradually less windy and less convective but stay generally cooler than normal for the period. Saturday and Sunday the cool north/northwesterly flow will dry out as a ridge of high pressure is very slowly approaching the regions.Wednesday Night: Freezing Level: Valley Bottom. Precip: 2/5mm – 4/10cm Wind: Light gusting Strong NWThursday: Freezing Level: Valley Bottom. Precip: 3/6mm – 5/10cm Wind: Moderate W gusting Strong/Extreme W Friday: Freezing Level: Valley Bottom. No significant precip expected. Wind: Light North.Saturday: Freezing Level: 500m No significant precip expected. Wind: Light, SE
Avalanche Summary
A report of a recent natural cycle trickled into the office Wednesday. The cycle reportedly occurred in both tree line and alpine elevation bands but poor visibility limited observations. The March 09 Surface Hoar continues to be sensitive to human triggering, a skier triggered a size 2 avalanche at 1400m on the surface hoar Tuesday. 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 10 - 20 cm of new snow out of Wednesdays storm which adds to the 20-40 cm snow that the region has received over the last few days. This 30 - 60 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 on a variety of aspects. I suspect cornices have become well-developed and could easily become unstable with daytime heating. 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.