Multiple snowpack weaknesses are in play and Wednesday's wind forecast would like to offer one more - new wind slab formation in places our new snow hasn't been sealed off by a surface crust.
Extra caution is needed at alpine elevations where crust or moist snow may have failed to form on the snow surface on Tuesday. These areas will have an ample supply of loose snow for forecast strong winds to form new and reactive slabs with on Wednesday.
A crust that formed in early January has been bonding poorly to the overlying snow. With the recent new snow load, this crust is now buried 60 to 80 cm deep, a prime depth for human-triggering as well as large, consequential avalanches.
Up to 40 cm of new snow was reactive where storms slabs formed over a recent crust on Tuesday. This reactivity may persist through Wednesday.
No recent avalanches have been reported, but there have likely been natural avalanche cycles during the recent storms. Large human-triggered avalanches will continue to be a concern on Wednesday due to a combination of recent snow, increasing winds, and a potential weak layer and crust buried 60 to 100 cm deep.
Warm temperatures on Tuesday likely allowed for a melt-freeze crust to form on the surface at all but high alpine elevations. This crust will top wide-ranging and rapidly settling new snow amounts of 10-40 cm from Monday night. Everywhere a crust has formed, it should prevent Wednesday's forecast strong winds from forming new wind slabs.
Storms over the past week deposited 70 to 110 cm over a thin crust layer above 1000 m. This crust has been highlighted as a critical avalanche layer in recent snowpack tests. Frequent rain has been eroding the already thin snowpack below this elevation.
Snowpack depths at treeline are around 120 cm, tapering quickly with elevation. Although the snowpack in most forested areas below treeline remains below threshold depths for avalanches, many steep bluffs, cutbanks, and alpine features in the upper below treeline band are capable of producing avalanches.
Tuesday night
Mainly clear. Light southeast winds.
Wednesday
Becoming cloudy with flurries bringing up to 5 cm of new snow by end of day and increasing overnight. Strong southeast winds. Treeline high temperatures around 0°C with freezing levels around 1300m.
Thursday
Stormy weather with 15-20 cm of new snow from the overnight period and another 15-30 mm over the day as snowfall shifts to rain at all but high alpine elevations, continuing overnight. Extreme south winds. Treeline high temperatures reaching +3 as freezing levels climbs from 1000 to 1800 m throughout the day.
Friday
Cloudy with continuing heavy rain at all but highest alpine elevations. Extreme south winds. Treeline high temperatures around +4 with freezing levels between 1800 to 2100m.
More details can be found in the Mountain Weather Forecast.
