Make a plan to step back from avalanche terrain and away from overhead hazard as the storm progresses and avalanche danger increases over the day. Surface slides entraining recent accumulations or stepping down to the previous storm interface could result in surprisingly large and destructive avalanches.
In higher snowfall parts of the region, increasingly deep accumulations of low density snow that hasn't formed into a slab may continue to produce large sluffs with rider traffic in steep areas.
Up to 25 cm of new snow by end of day and strong southwest winds will create an increasingly hazardous storm slab problem over the day on Thursday. Storm slabs may also entrain recent accumulations from the last storm to create larger, more destructive avalanches.
Observations since the weekend storm have shown mainly small dry loose avalanches releasing naturally, especially on steep, sunny slopes, as well as with skier traffic. We expect some degree of a slab avalanche cycle also took place at higher, wind affected elevations over the weekend, particularly in areas like Pine Pass and the MacGregors, where up to about 40 cm of new snow accumulated with strong southwest winds.
Earlier in last week there was evidence of deep persistent slab activity that occurred during a previous storm with avalanches up to size 3.5. While we currently expect the deep weak layer to be dormant, riders should continue to avoid steep, thin, rocky slopes where triggering a deep persistent avalanche would be most likely, particularly near alpine ridgelines.
Looking forward, moderate snowfall and high winds are expected to trigger an uptick in natural avalanche activity and human triggering potential through Thursday.
Roughly 10-20 cm of new snow is expected to accumulate in the region by end of day Thursday. For the most part it will add to low density storm snow from the weekend (20-40 cm of it in the west of the region, closer to 5-15 in the east), but it may also bury recent wind slabs in more exposed areas.
The recent variable storm totals overlie faceted (sugary), heavily wind affected snow from previous cold temperatures and north winds. This interface remains somewhat in question with storm slabs being generally slow to form over it in recent days.
The middle of the snowpack is generally strong.
A weak layer of large and weak facets is found near the base of the snowpack. The layer is currently considered dormant, except perhaps in very steep alpine terrain that is inherently shallow. Riders should continue to avoid thin, rocky terrain where the likelihood of triggering this layer is higher.
Wednesday night
Continuing snowfall bringing 5-10 cm of new snow. Strong to extreme southwest winds.
Thursday
Cloudy with continuing snowfall bringing 5-15 cm of new snow, continuing overnight. Strong southwest winds easing over the day. Treeline high temperatures around -9.
Friday
Cloudy with easing flurries bringing up to about 5 cm of new snow, including overnight amounts. Storm totals to 25-35 cm. Moderate southwest winds. Treeline high temperatures around -10.
Saturday
A mix of sun and cloud with isolated flurries. Light to moderate northeast winds. Treeline high temperatures around -15.
More details can be found in the Mountain Weather Forecast.
