Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
Warm air enters the region late Sunday persisting through mid-day Monday. Freezing levels are forecast to be between 1500 - 2000 m & winds in the alpine will be ripping out of SW @ 55 -95 k/hr A cold front moves in after lunch Monday lowering freezing levels and bringing light snowfall, 5 cm or so are expected Monday night. A weak ridge builds in Tuesday AM before a more organized low moves in Tuesday afternoon into Wednesday. We can expect 15 - 20 cm before the system exits to the east Wednesday afternoon.
Avalanche Summary
Storm snow avalanche activity has greatly diminished. Continued NW winds are driving wind slab formation in exposed areas. A size 2.5 avalanche was reported from the region on a steep unsupported SE facing slope New Years Eve. While activity on the surface hoar has slowed down, I'm still very suspect of this persistent weakness at all elevation bands.
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 both the alpine and treeline. Wind slabs can also be found in wind exposed areas below treeline. The mid December surface hoar/facet/crust interface is buried anywhere from 80-100cm deep. While avalanche activity on this layer has slowed, 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. Obvious signs of instability (whoomphing, shooting cracks, etc.) are lessening. However, 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.