Regions
Northwest Coastal.
Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Moderate-heavy amounts of snowfall are expected Tuesday night into Wednesday morning. Accumulations 15-25cm tonight, 15-20cm on Wednesday. Ridgetop winds from the West near 75km/hr overnight, tapering off to 40km/hr from the NW on Wednesday. Thursday may bring some flurries, but mainly dry, cooler conditions with the associated ridge. Freezing levels will remain at valley bottom. Friday brings light snowfall, and changing moderate outflow winds from the East.
Avalanche Summary
One natural size 2.5-3 was reported from Mt. Rainy occurred in the evening with additional precipitation and warming. One size 1 skier triggered avalanche occurred on a SW aspect @ 1400m. Crown depth was 5-10cm, the width 20m, running 20m.This ran in the current storm snow. Reports of natural sluffing on steep terrain features. With forecast wind and snow, avalanche activity may increase.
Snowpack Summary
Generally, up to 35 cm of new snow sits over a strong melt freeze crust that exists below 1000m on all aspects, and over wind-pressed powder on shaded alpine features. Facets and surface hoar have been found sandwiched between the newer snow and the old surfaces at treeline and below. This surface hoar seems to be more predominant in inland areas. Where it exists, this layer has started to become reactive under the new load and slab development. I suspect this will continue as the forecast snow and wind continues. Check out our Forecaster's Blog for some insight on incremental loading. The mid and lower snowpack is generally well settled and strong.
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.
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.