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Big crowns and wind slabs
Location Name:
BNSF Avalanche Safety - Snowslip Mtn GNP
Observation date:
Thursday, February 25, 2021 - 22:45
Is this an Avalanche Observation:
Yes
Observation made by:
Public
Location
Tabs
Quick Observation
Ascended the ridge above the Burnout, Shed 4D, Shed 5, and Shed 7 avalanche paths. Descended the Shed 5 path.
Objectives were to check out the crowns from the recent avalanches in Shed 7, assess the wind-loading, and assess the snowpack structure and stability in this area with special attention paid to the weak layers associated with the Jan. 13th crust.
Made it to the crown of the large hard slab avalanche (destructive size 3 of 5 – D3) in Shed 7 east which was about 2-4’ thick at this location with a slope angle of about 30°. The failure layer for this avalanche was indeed a layer of facets above the Jan. 13 crust (details in pit profile).
The large hard slab avalanche (D3) in Shed 7 West was likely triggered by a falling cornice. The crown ranged from 2-5 feet thick and it appeared that much of the overhanging part of the cornice above the crown failed as well. Again, the failure layer was a layer of facets above the Jan. 13 crust.
Moderate to strong SW winds were heavily loading easterly aspects above 5500’. Ski cuts on small test slopes resulted in some minor cracking and little 3-4’ slabs. In some locations new wind slabs were nearing 3’ feet thick.
No audible collapses or any other signs of instability observed.
Dug a hasty pit and performed two Extended Column Tests (ECT) in the Burnout path at around 5000’ elevation on an easterly aspect. Snow depth was 52” and the Jan. crust was buried about 30” down. ECTP26 on a layer of weak facets above the crust.
A crust from Tuesday, Feb. 22nd was present on the Canyon floor up to around 4800-4900’ elevation.
Full on storm day with obscured skies, snow (S2) at times, and moderate to strong westerly winds above 5500’.
Daytime high air temperatures reached the mid-20s °F on the Canyon floor and the mid-teens °F above 6000’.
Snowpack, Avalanche, Weather Images:
Travel Details
Region:
Flathead Range/Glacier National Park - John F. Stevens Canyon
