Warm temperatures and heavy precipitation are increasing the avalanche danger in the days to come. Good time to avoid avalanche terrain or to make very conservative terrain choices out there.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
Tuesday night and Wednesday: The strong Westerly flow bringing significant precipitation amounts into the interior should taper off a little tonight but should keep delivering moisture until Friday. Amounts vary in the region from around 10-20 mm. in water equivalent till Wednesday evening with winds blowing strong from the W. Freezing levels are expected to rise to close to 2000 m. during the day and stay high until Friday.Thursday: Similar amount of precipitation and freezing level is expected for Thursday with slightly lighter winds from the SW.Friday: The Westerly flow is forecasted to weaken and precipitation to taper off. Freezing levels and wind speeds should also start to drop.
Avalanche Summary
A couple slab avalanches size 1 have been triggered by skiers out of steep alpine terrain on a S and NE aspect. These would have initiated in ~30 cm deep wind loaded pockets. There was also a couple natural slab avalanches up to size 2 one of which was triggered by a cornice fall on a NE alpine slope. More and bigger avalanches are expected in the days to come.
Snowpack Summary
Currently, 5-20 cm of new snow (more in the W part of the region) is covering a variety of surfaces; a 2 cm thick suncrust on SE-S-SW facing slopes at all elevation, a melt-freeze crust all the way up to 1600 m. and some well developed surface hoar on shaded slopes above that elevation. The forecasted precipitation and warm temperatures will add a good load to the snowpack (could be another 30 mm in water equivalent till tomorrow night). The variety of surfaces described earlier are already showing reactivity to this new load and creating a good failure plane for avalanches to slide on. With freezing levels rising again tomorrow, the new dryer snow layer at the upper below treeline and treeline elevation band (between ~1200 m. and ~1800 m.). could get soaked and create wetslabs and loose wet avalanches. The surface hoar persistent weak layer buried down up to 100 cm is still producing some sudden planar snowpack test results. This layer could be triggered by the heavy load in the coming days.
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.