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Wind slabs in the Program Area
Location Name:
BNSF Avalanche Safety - Snowslip Mtn. GNP
Observation date:
Thursday, December 16, 2021 - 22:30
Is this an Avalanche Observation:
Yes
Observation made by:
Public
Tabs
Quick Observation
Climbed the ridge dividing the Shed 6 and Shed 7 avalanche paths to the Shed 7 weather station at 6300’. Descended the Shed 5 path.
Objectives were to observe recent snowfall totals and the extent of recent wind-loading, look for recent avalanche activity, and complete a snowpack profile in Shed 7.
Intentionally triggered a small wind-slab in Test Slope 3 at 5600’ on a SE aspect, SS-AS-D1.5-R3-I. Crown was about 30’ wide and 4” to 12” thick (photo). Debris ran about 100’ terminating well above the grade.
No other avalanche activity observed.
Snow depths are building quickly with a settled base of 15-20” on the Canyon floor and 2-4’ at elevations above 6000’.
Active wind-loading above 5000’ elevation due to moderate westerly winds with fresh wind slabs building, primarily on easterly aspects. In addition to the above-mentioned avalanche, observed a few shooting cracks 5-20’ long in these fresh wind slabs.
Dug a snow pit at 6350’ on an east aspect near the top of the Shed 7 East avalanche path. Total snow depth was 45” consisting of right-side up layering until a layer of rounding facets near the ground resting on top of an 8” thick laminate of alternating layers of crusts and facets (snow profile). No propagating fractures with an Extended Column Test.
Overcast skies with snowfall (S-1 to S2), and moderate westerly winds above 5000’ with calm or light winds on the Canyon floor. Another 1” of low-density snow today fell today.
Daytime highs reached the low-20s °F on the Canyon floor and the mid-teens °F above 6000’ elevation.
Snowpack, Avalanche, Weather Images:
Travel Details
Region:
Flathead Range/Glacier National Park - John F. Stevens Canyon
Activity:
Skiing
Avalanche Details
Avalanche Details:
Date and Time of Avalanche:
Thursday, December 16, 2021 - 13:00
Number of avalanches:
1
Avalanche Type:
Soft Slab
Failure Plane/Weak Layer:
New/old snow interface
More information or comments about the avalanche:
Trigger
Trigger:
skier
Trigger Modifier:
Intentionally Triggered
Terrain
Aspect:
Southeast
Starting Elevation:
near-treeline
Size
Destructive Size:
D1 Relatively harmless to people.
Relative Size:
R3 Medium
Crown Height:
Less than 1 ft
Avalanche Length (Vertical Run):
100ft.
Avalanche Width (Average width):
30ft.
Avalanche Location:
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