Wind is a critical factor and changing winds may build fresh and reactive wind slabs.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
Arctic air continues to be entrenched in the South Rockies. The pattern will start to shift Thursday to a zonal flow, allowing Pacific frontal systems to make way into the region early next week. Little change is expected for the weekend.Thursday/ Friday/ Saturday: Mix of sun and cloud with a strong alpine inversion bringing temperatures near -15 and valley bottoms -20. Ridgetop winds light-moderate from the West.
Avalanche Summary
On Tuesday, ski cutting produced numerous size 1-1.5 loose dry avalanches from steeper terrain features. Switching winds on Thursday may build new and reactive wind slabs. Variability in the winds has been the name of the game and wind slabs may be found on all aspects at upper elevations. Persistent slab avalanches also remain an ongoing concern, creating a low probably, high consequence problem for the region. Extra caution is recommended in shallow snowpack areas.
Snowpack Summary
15-20 cm of recent snow has buried variable old snow surfaces which consists of heavily wind scoured surfaces or old wind slabs in exposed terrain, surface hoar in sheltered terrain, and/or widespread faceted old snow. Recent moderate winds from a variety of directions is expected to have redistributed some of this new snow on leeward slopes. The mid pack appears to be quite variable throughout the region and the structure is dependant on snow depth. In deeper snowpack areas, the snowpack appears to be well settled and right side up with isolated concerns for the mid-December weak layer. In shallow snowpack areas and lower elevations, the snowpack is heavily faceted and there are concerns for the mid-December weak facet layer as well as weak basal facets. Due to inconsistencies in snowpack structure throughout the region, its a good idea to dig down and test weak layers in your local riding area.
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.