Valanga

East of WMR

Mark DundasWhitefish Range
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Foto dell’osservazione 1Foto dell’osservazione 2Foto dell’osservazione 3Foto dell’osservazione 4Foto dell’osservazione 5

Quick report

Cracking
specific

Riders in the southern Whitefish Range triggered multiple storm slab avalanches over the past few days. We traveled in this terrain to take a closer look at these slides.

  • We viewed six triggered avalanches on a mid-elevation east aspect just east of the WMR boundary line. They were D1, D1.5, and D2 destructive size.
  • Some failed at the density change between the Thursday and Friday storms, while others failed on a stout crust beneath the recent snow. The crown depth varied between 6 and 12 inches. 
  • Two of these slides traveled a long distance on the crust, terminating on the flat bench below the starting zones. We don't believe any of these stepped down beneath the crust.
  • We triggered loose dry avalanches on very steep slopes in the 3" snow that fell in the past 24 hours. These sluffs ran on top of the previous day's slightly denser snow. 
  • We were unable to trigger soft slab avalanches today. The best we could do was remove large blocks of hangfire above crowns on steep slopes. 
Cracking was observed at the surface in the 3" snow that fell over the past 24 hours. Shooting cracks down 12" to a crust were noted only in hangfire on very steep, unsupported slopes.

Weather

Air Temp
25
Cloud Cover
obscured
Wind Loading
none
Rain Elevation
3000
Recent Snowfall
10
Snow Avail For Transport
moderate amounts

Poor to very poor visibility throughout the day. Snow began around 1000 at S2 and ended around 1330. I'm not sure what happened after leaving at 1415. The wind was calm through the morning but became light to moderate in the afternoon out of the south-southeast.

Snowpack

A full-depth pit at 6400' on an east aspect. HS=175 cm. 8 cm of recent F hard snow rests on 22 cm of 4F hard snow. This recent snow caps a 15 cm thick knife hard crust. An 8 cm thick layer of 4F-facets lurks beneath the crust. This rests on a 1F-Pencil hard mid-pack that is 70 cm thick. A 50 cm thick block of moist snow comprises the base of the pack.

CT 11, 13 down 30 cm on top of the crust.

No propagation in the large column test: ECTN 12, 13

Avalanche

Size
D1.5 R2
Type
SS
Aspect
E
Trigger
AS
Elevation
6400 ft

This summarizes five rider-triggered storm slab avalanches that were not reported to FAC staff. These likely failed on 3-13 and 3-14 and were D1, 1.5, and 2. Only the two largest traveled to the bottom of the path. A snowboarder may have triggered one or two, with the skiers responsible for the rest.