Watch for signs of wind slabs on all aspects as wind direction is expected to reverse on Tuesday. Buried persistent weak layers also remain a concern and avalanches have the potential to step down to a deeper layer.
Confidence
Moderate - Wind speed and direction is uncertain
Weather Forecast
Mostly cloudy conditions are expected for Tuesday with lingering flurries in the morning. Treeline temperatures are expected to fall to around -20C and alpine winds are forecast to be moderate to strong from the north. Sunny conditions are expected for Wednesday and Thursday with treeline temperatures around -15C during the afternoon and -25C overnight. Alpine winds are forecast to be light from the northeast on Wednesday and moderate from the northwest on Thursday.
Avalanche Summary
No new avalanches were reported on Saturday or Sunday. On Tuesday, recently formed wind slabs are expected to remain reactive to human triggering. Ongoing wind loading is also expected on Tuesday with the forecast for moderate to strong northerly winds in the alpine. With the winds switching directions, wind slabs should be expected on a variety of aspects. Persistent slab avalanches also remain an ongoing concern. Buried weak layers are creating a low probably, high consequence problem for the region.
Snowpack Summary
10-20 cm of new snow on Monday with moderate winds will recharge our wind slab problem, feeding existing slabs with additional load and forming new slabs in the lee of exposed terrain features. Winds have been switching directions recently and wind slabs should be expected on all aspects. The mid snowpack is generally right side up, with the mid-December interface down 40-80cms, giving inconsistent results in snowpack tests. There is some faceting below this interface but resistances are good and showing signs of rounding and stabilizing. Travel conditions have been challenging (especially at lower elevations) and little change is expected until a significant warm up helps to settle the snowpack.
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.