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BNSF Avalanche Program - Snowslip Mtn. GNP
Location Name:
BNSF Avalanche Program-Snowslip Mtn. GNP
Observation date:
Monday, December 2, 2019 - 16:00
Is this an Avalanche Observation:
Yes
Observation made by:
Public
Tabs
Quick Observation
Toured through the upper elevations of the Shed 7 East, Shed 7 West, and Shed 5 avalanche paths.
Objectives were to observe snow depths and snowpack structure above the railway grade as the 2019-20 winter snowpack continues to develop.
Overcast skies with very light or light (S-1 or S1) snowfall all day with moderate SW winds above 5000 ft. elevation.
Air temperatures hovered in the low to mid-20s °F above 6000 ft. elevation and warmed to just above freezing at the Canyon floor by early afternoon.
Snow depths around 5000 ft. elevation varied between 10-15 inches and above 6000 ft. typically ranged between 1-2 feet. Previous wind transport from last week’s N-NE winds was notable on S-W aspects, especially above 5000 ft. with old wind slabs up to 3-4 ft. thick in exposed locations such as the Shed 6/7 ridge.
New wind slabs from today’s SW winds were still relatively small, about 6-8 in. thick and generally less than 20 ft. across.
Ski cut one small new wind slab, 6-8 in thick x 10-15 ft. wide on a SE aspect slope at about 5500 ft.
Conducted a full snow profile at 6300 ft. elevation, SE aspect, in the very upper reaches of the Shed 7 East avalanche path (photo of profile below).
Total snowpack depth at profile location was 24 in. The snowpack structure was poor with a cohesive slab capping a layer of weak facets sitting on top of a firm melt-freeze crust.
Stability tests resulted in:
ECTP22 on this layer of facets about 13 in. from the snowpack surface (1st test)
ECTN23 on the same layer of facets but fracture propagated across only half the column (2nd test).
Save for the one very small ski cut wind slab mentioned above, no avalanche activity observed.
Snowpack, Avalanche, Weather Images:
Travel Details
Region:
Flathead Range/Glacier National Park - John F. Stevens Canyon
Activity:
Skiing
Snowpack Details
Snowpack and Weather Details:
Terrain
Elevation of observation:
5000-6500 ft
Above 6500 ft
Aspect(s) of observation:
E
SE
S
Persistent Weak Layers:
Facets or Faceted Crust
Buried
Total Snow Depth:
24
Blowing Snow:
Moderate
Wind Speed:
Moderate (Small trees sway)
Wind Direction:
Southwest
Air temperature:
Below Freezing
Sky Cover:
Overcast (OVC)
Highest Precipitation Rate:
Light Snowfall (S1)
Avalanche Details
Avalanche Details:
Date and Time of Avalanche:
Monday, December 2, 2019 - 14:00
Number of avalanches:
1
Avalanche Type:
Unknown
Failure Plane/Weak Layer:
New/old snow interface
More information or comments about the avalanche:
New wind slabs from today’s SW winds were still relatively small, about 6-8 in. thick and generally less than 20 ft. across.
Ski cut one small new wind slab, 6-8 in thick x 10-15 ft. wide on a SE aspect slope at about 5500 ft.
Trigger
Trigger:
skier
Trigger Modifier:
Intentionally Triggered
Terrain
Aspect:
Southeast
Starting Elevation:
near-treeline
Size
Destructive Size:
D1 Relatively harmless to people.
Crown Height:
Less than 1 ft
Avalanche Width (Average width):
12ft.
People Involved
Number of people caught:
0
Number of partial burials:
0
Number of full burials:
0
Avalanche Location:
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