Avalanches are expected today with snowfall and wind loading weak layers. Avalanches have been running fast and far onto avalanche fans. Minimize your exposure to avalanche terrain, including while traveling across paths in the valley bottom.
Weather Forecast
We should get 10cm of snow today (on top of the 8cm that fell overnight), with strong SW winds gusting to extreme. Freezing levels may rise to 1500m. On Friday, another 10cm of snow is forecast with strong SW winds. Over the weekend, snowfall and the winds should taper off and we may see some sunny breaks.
Snowpack Summary
30cm of settled snow sits on a weak layer of large snowflakes which are reactive in tests. The Dec 8 PWL, which is surface hoar at lower elevations and facets and variable wind slabs at higher elevations, is down ~80cm. This layer is becoming less reactive in tests. The Nov 28 surface hoar, down ~1m, is still reactive in some locations.
Avalanche Summary
No new avalanches were observed yesterday. Recent avalanche activity has been triggered by wind-loading, with avalanches to size 2.5 running into avalanche fans. As the storm builds, winds are forecast to increase as well. With lots of snow available for transport, wind loading will magnify precipitation rates and natural avalanches are expected.
Confidence
Intensity of incoming weather systems is uncertain
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.
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.