Monitor new snow depth and wind redistribution closely as Wednesday's storm makes its way into the region. Be prepared to dial back your terrain selection if snowfall exceeds forecast amounts. Avoiding wind-exposed areas will be a good strategy for the day.
Wind slabs of varying age and reactivity can still be found in the alpine and upper treeline, with northeast to northwest aspects likely to hold the most recent slabs as a result of mainly south winds. This problem won't get much of a chance to stabilize before another pulse of new snow and wind creates new slabs to manage on Wednesday.
Monday night: Clear periods. Light to moderate southwest winds, easing into the morning.
Tuesday: Becoming cloudy with scattered flurries bringing up to 5 cm of new snow, mainly in the south of the region. Light southwest winds. Alpine high temperatures around -7.
Wednesday: Cloudy with flurries bringing 5-10 cm of new snow, with possible locally enhanced amounts, continuing and easing overnight. Moderate to strong south or southwest winds. Alpine high temperatures around -5.
Thursday: Mainly cloudy with isolated flurries and a trace of new snow, increasing a bit overnight. Light to moderate south or southwest winds, increasing overnight. Alpine high temperatures around -5.
Reports from the past several days have highlighted wind slab problems at higher elevations, with observations from Bullmoose, Hasler, Torpy, and Pine Pass all showing strong evidence of the problem. These reports suggest a good transition from more widespread storm slab conditions observed a day earlier in the Sentinel Pass area.
Explosives control work in the Sentinel Pass area on Friday revealed a touchy storm slab problem at alpine and treeline elevations. Seven out of eight explosives produced avalanches from size 2 to 2.5 (large). Crown fracture depths were approximately 40 cm, the height of recent snowfall in the area. None of these avalanches stepped down to a persistent weak layer.
Looking forward, our wind slab problem won't get much of a chance to stabilize before new snow and elevated winds complicate matters again on Wednesday. Forecast snowfall varies over the region, so it will be important to assess new snow depths over the day on Wednesday and again on Thursday morning to determine the scale of any new wind slab problem or whether the greater concern is a skiff of snow obscuring slabs lingering from the last storm.
Recent snow has settled with warm temperatures and been blown around by wind from various directions, resulting in wind slabs on all aspects at and above treeline. These are expected to be on a positive stabilizing trend under the current pattern of mild weather, but new snow and wind should shake things up on Wednesday.
A weak layer of surface hoar buried in late December remains a concern but seems to be gaining strength. This layer has been found across much of the North Rockies region, but has seemed to be more problematic in particular areas, such as around McBride and the McGregors/Torpy. It seems to be most readily found in sheltered treeline features 50 to 150 cm below the surface.
