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Looking for instability
Location Name:
BNSF Avalanche Safety - Wahoo Ridge/Path 1183
Observation date:
Friday, April 3, 2020 - 23:00
Is this an Avalanche Observation:
Yes
Observation made by:
Professional Observer
Tabs
Quick Observation
Ascended the ridge to the north of and above Cascadilla Creek to gain access to the upper starting zone (around 5900 feet) of the 1183 avalanche path.
Descended the ridge located on skier’s left of Path 1183 and to the east of Wahoo Creek.
Objectives were to look for any recent avalanche activity, observe recent snowfall totals, and further investigate the snowpack structure and persistent slab problem that has been reported in the Flathead Range.
3-5 very small (D1) skier triggered loose snow sluffs in the lower runout zone of Path 1183 (~4000 feet, north aspect) with debris running 50-100 feet.
No slab avalanche activity observed.
Sunday’s (3/29) rain line extended up to about 5300 feet as evidenced by a very stout, supportable, and slippery crust up to this elevation. Skinning was challenging at times. New snow depths on top of this crust ranged from 5-10 inches. No buried facets observed on top of the 3/29 crust and no real signs of instability save for the loose snow sluffing mentioned above.
Above 5300 feet the recent snow depths increased quickly. Depths down to the 3/24 interface ranged from 20-30 inches and was right side up in hardness with Fist-hard on top, firming up to 4F-hard going down the column.
Many hand pits revealed a poor snowpack structure in most locations above 5300 feet with facets on crust layers and/or facet layers sandwiched between crusts associated with the 3/24 interface.
However, in the terrain we travelled through we did not observe any direct signs of instability such as collapses, shooting cracks, or slab releases on small test slopes.
Also no propagating results observed in two different Extended Column Tests. The first at 5700 feet on a north aspect and the second at about the same elevation on an east aspect. We did get some ECTNs within the different storm layers from the last week.
Overcast or obscured skies with snowfall ranging from S-1 to almost S5 for short, 10-15 minute intervals.
Winds were calm or light and coming from variable directions, sometimes west/southwest, and at other times from the east.
Snowpack, Avalanche, Weather Images:
Travel Details
Region:
Flathead Range - Middle Fork Corridor
Activity:
Skiing
Avalanche Details
Avalanche Details:
Date and Time of Avalanche:
Friday, April 3, 2020 - 14:15
Number of avalanches:
5
Avalanche Type:
Loose Dry/ Sluff
Failure Plane/Weak Layer:
Within storm snow
Trigger
Trigger:
skier
Trigger Modifier:
Intentionally Triggered
Terrain
Aspect:
North
Starting Elevation:
below-treeline
Size
Destructive Size:
D1 Relatively harmless to people.
Relative Size:
R1 Very Small
Avalanche Length (Vertical Run):
75ft.
Avalanche Location:
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