Weather Forecast
The region will continue to see unsettled weather conditions overnight Monday, bringing light snow, and moderate NW winds. Freezing levels will fall to valley bottom. Tuesday: Mainly dry conditions. A mix of sun and cloud in the morning. Increased cloud and light flurries during the afternoon. Freezing levels remain valley bottom. Wednesday/Thursday: Continued cloud, and light snow amounts. Ridgetop winds moderate from the NW. Treeline temperatures -12, rising to -4. Freezing levels fluctuating from valley bottom to 12-1500m Wed/Thurs afternoon.
Avalanche Summary
A natural avalanche cycle is under way, however poor weather is limiting observations. Natural, skier-remote and accidental avalanches were observed on Sunday to size 2. Avalanches reported throughout the week illustrate the unpredictable nature of persistent weak layers in the upper snowpack. Most failed on upper snowpack persistent weaknesses. These layers are touchy and are likely to fail under the new storm load, creating large or widely-propagating avalanches.
Snowpack Summary
Over the weekend, 60-100 cm snow has fallen. Strong winds and fluctuating temperatures are creating storm slabs and wind slabs on a widespread basis. Persistent weak layers (surface hoar, facets, crusts) buried in February are the main concern at all elevations and could be easily triggered by storm slabs, wind slabs or sluffs, or with a light additional load (like a sled or skier). Avalanches may be unexpectedly large, given the amount of fresh snow. Large cornices are forming, and may act as potential triggers for deep avalanches.
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.
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.