There is much uncertainty surrounding the March 10 Surface Hoar and how it will respond to Wednesdays storm. Hedge your bet and stick to simple terrain free of overhead hazard.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period
Weather Forecast
Synopsis: A low pressure system approaches from the SW which should deliver strong wind and significant precip. A trailing cold front in it’s wake will bring the freezing levels down to valley bottom on Thursday. Wednesday: Freezing Level: 1500m. Precipitation: 15 /20mm – 30/40cm Wind: Strong SWWednesday night: Precipitation: 10/15mm – 20 – 30cm.Thursday: Freezing Level: Valley Bottom. Precipitation: Isolated convective flurries. Wind: Moderate to strong NW.Friday: Freezing Level: Valley Bottom. Precipitation: Isolated convective flurries. Wind: Moderate NW.
Avalanche Summary
No new avalanche was reported Sunday. A natural avalanche cycle to size 2.5 took place in response to new snow loading on Saturday night.
Snowpack Summary
Generally moderate amounts of new snow fell on Saturday night and Sunday and have have been distributed by strong northerly winds into deeper windslabs in lee terrain. Depending on elevation, these recent accumulations may overlie a thick rain crust. Up to 1m below the surface is a layer surface hoar or a sun crust buried on March 10th. I expect another round of natural activity on this layer as the coming storm adds a significant new load on Wednesday. At lower elevations where last week's heavy rain saturated the snowpack, subsequent cooling has dramatically strengthened the snow.Weaknesses lower in the snowpack have become unlikely to trigger.Widespread cornice development has also taken place, and cornices are reported to be very large and weak.
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.
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.