The freezing level is forecast to rise in conjunction with snow and/or rain. This could be enough make any of the deeper buried weak layers reactive again in the coming days.
Confidence
Moderate - Freezing levels are uncertain on Tuesday
Weather Forecast
TUESDAY: Periods of snow, accumulation 10-15cm / Light to moderate south wind / Alpine temperature 0 / Freezing level 2000m WEDNESDAY: Flurries, accumulation 5-10cm / Light to moderate southwest wind / Alpine temperature -3 / Freezing level 1500mTHURSDAY: Flurries, accumulation 5-10cm / moderate to strong south wind / Alpine temperature -4 / Freezing level 1300m
Avalanche Summary
Recent reports indicate both natural and human triggered wind slab avalanches in alpine and tree line lee terrain to size 1.5. Earlier last weekend, explosive control and ski cutting produced numerous small storm slabs (size 1-1.5) and two size 2 storm slabs up to 50 cm deep. Most failed within the storm snow, but a few on the mid-March rain crust.On Tuesday, wind slabs may remain reactive in human triggers and at upper elevations the deeper mid-February weak layer continues to present a low likelihood of triggering yet would produce a large avalanche and thus a high consequence if triggered.
Snowpack Summary
Expect an additional 10-15cm of new snow through the day today to add to the 30 cm of storm snow from last weekend, which sits above a widespread rain crust up to 2200m. Thicker wind slabs and large cornices likely exist in alpine terrain. Reports suggest the storm snow is generally well bonded to the crust, and cooling temperatures should help stabilize the upper snowpack. The mid-February crust/facet layer is now 80-120 cm deep and may be up to 200 cm deep in wind loaded terrain. This layer was reactive prior to recent warming events, but now there's some uncertainty as to how long it will remain reactive.
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.