The hazard may go higher than forecast if precipitation amounts are greater than expected.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
A series of Pacific cold fronts will move into the area late today ( Friday ) and leave 5 to 10 cm of snow at upper elevations., Winds will be moderate to strong from the south west. Freezing levels should drop to 1000m for the next few days, with daytime heating raising the freezing level to 1500m for Sunday and around 1700m for Monday afternoon. Monday may see another 5 cm of snow at upper elevations.
Avalanche Summary
Little in the way of avalanche activity from yesterday. Moist loose avalanches had been reported earlier in the week, but with falling temperatures this activity has gone dormant. Expect wind slab activity with new loading and strong winds.
Snowpack Summary
5 to 15cm of incoming precipitation will fall on a variety of crusts and old surfaces including surface hoar and facets that formed in sheltered locations during the recent clear weather. Moderate to strong south west winds will redistribute the storm snow into wind slabs on the lee sides of ridge tops. A facet/crust layer that was buried in mid-March is now approximately 50-100 cm down. Recently it was found down 55 cm near the Duffey Lake Road, and produced moderate sudden results. This remains a concern in the region because of it's potential for very large avalanches. Cornices are now large and mature and may collapse with increased loading, possibly triggering the deeply buried weak layer.
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.