Storm problems will persist on Sunday, especially at higher elevations. If the sun breaks through, solar triggered avalanches are expected. Conservative decision making remains critical and travel in avalanche terrain is not recommended.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Another pulse of moderate-to-heavy precipitation is expected Saturday overnight with freezing levels around 1800m. Precipitation should ease during the day on Sunday but light scattered flurries are expected to persist, at least in the morning. Broken or scattered sky cover is possible in the afternoon and some areas may see sun. Freezing levels should remain around 1800m. Alpine winds are forecast to be strong from the SW on Sunday morning and ease during the day. The next storm pulse is expected to arrive Sunday overnight and persist through the day on Monday. Freezing levels may drop Sunday overnight but this depends on the amount of clearing between the storm pulses. Freezing levels on Monday are uncertain and may be as low as 500m or as high as 1500m. The end of the storms is forecast for early Tuesday. Lingering flurries and sunny breaks are both possible on Tuesday. Unfortunately, the warm air is expected to persist for several days following the end of the storm and freezing levels may remain unseasonably high.
Avalanche Summary
Natural, human-triggered, and explosive controlled avalanches up to size 2.5 were reported on Friday. This activity is expected to have continued on Saturday. On Sunday, natural avalanches remain likely at upper elevations where storm and wind loading continue. At lower elevations which have seen rain, natural activity is less likely but remains possible. Human-triggering remains very likely at higher elevations on Sunday. If the sun comes out on Sunday, solar aspects will likely see natural avalanche activity.
Snowpack Summary
Up to 60cm of recent storm snow has fallen over the late-Jan weak layer. Rising freezing levels during the storm have created upside-down snow conditions and highly reactive storm slabs. Rain has soaked the snow surface up to around treeline elevation. Strong SW winds have formed wind slabs in exposed leeward terrain features. The storm slab sits on an old rain crust at lower elevations, variable surface hoar, and/or wind affected surfaces at higher elevations. The mid-January surface hoar is typically down 60-100cm but may have been destroyed by warmth at low elevations. The mid-December weak layer is in the mid-pack down 80 to 120cm. Both of these persistent layers have been reactive recently. The mid-November weak layer of crusts and facets can still be found near the bottom of the snowpack. It has been unreactive lately, but should remain on your radar, especially in shallow snowpack areas.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.