Forecast very warm temperatures are a concern. Are we going to have a spring warm-up in January? Stay tuned for more information as we approach the weekend.
Confidence
Fair - Freezing levels are uncertain
Weather Forecast
Overnight and Thursday: Strong Northwest winds aloft diminishing overnight to moderate by late morning. Freezing levels rising during the day to about 2300 metres. Sunny periods with a chance of high clouds.Friday: Alpine temperatures should drop below freezing overnight if skies remain clear. Freezing level rising to about 2700 metres during the day. Light to moderate Northwest winds.Saturday: Continued warm air at alpine elevations. Light winds and mostly clear skies.
Avalanche Summary
No new avalanches reported. Suspect extreme Westerly winds and warm temperatures have developed hard wind slabs. Areas with snow available for transport may have continued to experience natural wind slab avalanches. Forecast warm temperatures, limited precipitation, and continued very strong winds are expected to develop hard wind slabs and decrease natural avalanche activity. Avalanches that are triggered are expected to be large due to the amount of recent storm snow. Large storm snow avalanches may step down to buried persistent weak layers resulting in very large destructive avalanches.
Snowpack Summary
Expect extensive wind transport and wind slab development in all areas of the region. Recent storm snow varies from 40-70 cm across the region and I suspect that in some alpine areas storm snow has been transported into slabs that are more than a metre thick. Persistent weak layers of buried crusts/facets/surface hoar continue to be a concern, and may have been the failure plane for recent large natural avalanches. Forecast very warm temperatures may result in loose wet avalanches or cornice falls that may trigger the persistent weak layers or the basal depth hoar. Strong solar radiation combined with above freezing temperatures in the alpine could create very touchy triggering on Southerly aspects.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.