Forecast snowfall amounts could vary across the region. Southern and western parts of the region could see considerably less snow, potentially resulting in lower avalanche danger. Be sure to make careful local observations.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
Tonight and Tuesday: A warm front moves through tonight bringing generally light precipitation, followed by the trailing cold front on Tuesday with stronger precipitation. Expect accumulations of up to 20 cm in some areas. The freezing level is around 900-1100 m and winds are strong to extreme from the SW-W.Wednesday: Precipitation should taper off with gradual clearing throughout the day. Temperatures drop with the freezing level returning to valley bottom by evening. Winds ease to light or moderate from the NW. Thursday: Mainly sunny and cooler. The freezing level should be at valley bottom with moderate northerly winds.
Avalanche Summary
Parts of the region reported a fairly large natural avalanche cycle late Saturday through Sunday morning, with several avalanches up to Size 3. Skier testing also produced a few avalanches up to Size 2, primarily in wind loaded terrain or on very steep convex rolls.
Snowpack Summary
Although recent accumulations have been highly variable, up to 60cm of snow now overlies the weak faceted crystals or small surface hoar which formed during the last cold snap. Rising temperatures are reported to have enhanced slab properties creating a more reactive "upside-down" snowpack, especially at lower elevations. Moderate to strong southwest winds have created dense wind slabs in exposed high elevation terrain.As of late there has been no reported activity on the late-November interface which consists of sun crusts on steep south facing slopes and surface hoar in sheltered areas. This layer, buried between 60-80cm below the surface, is generally considered to be "stubborn" to trigger; however, avalanches at this interface could have nasty consequences.
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.
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.