The snowpack is complex and quite variable right now. Buried weak layers remain reactive and conservative terrain selection remains critical.Extra caution is required during the heat of the day, especially on sun exposed slopes and around cornices.
Confidence
Low - Due to the number and quality of field observations
Weather Forecast
A mix of sun and cloud is expected for Friday with moderate southwest winds in the alpine. A temperature inversion is expected with a layer of above-freezing air sitting around 2000m elevation and colder temperatures in the valleys. A weak storm pulse is expected to bring 5-10cm to the region on Saturday morning. Alpine winds are expected to be moderate from the southwest on Saturday with freezing levels around 1600m. Mostly dry conditions are expected Saturday afternoon through Sunday morning before a second weak storm pulse arrives Sunday afternoon.
Avalanche Summary
On Wednesday, a natural size 3 glide crack avalanche was reported. This released on the ground down 3 meters on a south aspect at 2000m. Explosive control trigger five cornice release size 1.5-2.5 on north through east aspects. None of these cornice releases triggered slabs. On Tuesday, several natural size 1 loose avalanches were reported. Also reported was one natural size 2 loose avalanche from a northwest aspect at 2800m. On Monday, two size 2.5 cornice releases were reported from north aspects.
Snowpack Summary
Surface hoar growth is being reported in sheltered areas as well as near surface faceting. Wind affected surfaces are being reported in the alpine and large cornices are reported to be weak. The surface hoar and/or crust layer from early February is now down 70-90cm and remains reactive in snowpack tests. This layer is expected to become most reactive during the heat of the day, especially on sun exposed slopes.
Problems
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.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.