Heavy rain followed by alpine snowfall is Wednesday's recipe for rapidly changing and dangerous avalanche conditions.
Forecast weather suggests a substantial storm slab problem could form as rain switches to snowfall on Wednesday, particularly in the alpine. The greater the new snow accumulation, the more serious this problem will be.
Wednesday will be the second day of heavy rain saturating the snowpack. Steep slopes will remain likely places for wet loose avalanches to occur - especially with a human trigger.
Tuesday night: Heavy rain; 30-40mm. Strong to extreme south or southwest winds.
Wednesday: Heavy rain; 40 mm accumulation. Strong south or southwest winds. Treeline high temperatures around +4.
Thursday: Mainly sunny. Light variable winds. Treeline temperatures of -1 to -4, dropping over the day.
Friday: Mainly sunny, clouding over in the afternoon. Light variable winds. Treeline high temperatures around -1.
Wednesday's forecast suggests we may see another day of rapidly evolving avalanche conditions. If daytime freezing levels fall low enough we could see substantial storm slabs form in the region's upper elevations before the end of the day, particularly in alpine areas. A rapid transition from active wet loose avalanche conditions to a touchier new storm slab problem should be on your mind as new snow begins to accumulate.
Heavy rain has affected the snowpack at all elevations. Significant new snow (15-30 cm) may accumulate at high elevations during the final hours of the storm on Wednesday. This could set up a scenario where unstable new storm slabs become a serious concern before the end of the day.
Average treeline snow depths are around 80-100 cm with much of treeline and all but the uppermost below treeline elevations still below threshold depths for avalanches.
