Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
A ridge of high pressure drifts into the area Saturday evening driving overnight temperatures into the mid minus teens. On Sunday morning high clouds steam into the region ahead of the approaching mass of warm air. Light precipitation should begin after lunch, but I'm only expecting 5 - 10cm max for the day. The bigger story with the warm front is the rise in freezing levels which could go as high as 1500 m. Winds build to moderate/strong values out of the SW Sunday. A weak cold front affects the area Monday afternoon bringing another shot of light precipitation & lowering temps/freezing levels.
Avalanche Summary
Numerous avalanches from size 1 - 2 have been observed at all 3 elevation bands (BTL, TL, ALP), with failures occurring within the recent storm snow in the last 72 hours. Interesting to note that a size 3 was observed below treeline in the region Thursday, I suspect the mid December Surface Hoar was to blame.
Snowpack Summary
70-100 cm of total storm snow has fallen since Christmas. Winds have redistributed the storm snow into wind slabs that are widespread in the alpine. Wind slabs can also be found in wind exposed areas at and below treeline. The mid December surface hoar/facet/crust interface is buried anywhere from 80-100cm deep and remains a concern for backcountry users. Avalanche activity on this layer has slowed, but it remains a concern as incremental loading gradually adds more weight to this weak layer. Test profiles continue to show easy shears on this layer & there are reports of "whomphing" which is a collapse of this weakness. Slopes that have not avalanched in the last week are of particular concern for this persistent weakness. The lower snowpack is generally strong and well settled.
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.