Professional Observation
Basic Information
Observation Details
Observation Date:
December 22, 2021Submitted:
December 22, 2021Observer:
WCMAC - Geoff Fast and Hannah FastZone or Region:
Southern BitterrootsLocation:
Lost Trail BackcountrySigns of Unstable Snow
Recent Avalanches?
YesCracking?
None ExperiencedCollapsing?
None ExperiencedSnow Stability
Stability Rating:
FairConfidence in Rating:
HighStability Trend:
ImprovingBottom Line
- Facets buried deep (~100cm down) on shaded northerly aspects are rounding after additional snowfall and time, but the possibility to trigger a slab on this layer remains.
- Wind slabs likely in alpine above 7500 feet.
- New snow from 12/19 is bonding well to older snow, and upper snowpack has few concerns.
Media
Advanced Information
Weather Summary
Cloud Cover:
Mostly SunnyTemperature:
-1 C / 30 FWind:
Moderate , SW
Todays observations 12/22 - Mostly sunny skies, strong SW wind on ridgelines; Nearly reached freezing (0 C)
Previous wind scouring of S and W slopes and depositing on N and E slopes.
Past 5 days have seen temps in 20's, with slight rise above freezing previous day, and during avalanche activity.
Avalanche Observations
| # | Date | Location | Size | Type | Bed Sfc | Depth | Trigger | Comments | Photo |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Past 24 hours |
Lost Trail Backcountry - Wolverine Point NE 8000 |
D2.5 | SS | O-Old Snow | 100cm | AC-Cornice Drop | Likely during warming previous day. Crack, showing signs of cornice separating from mountain. Portion of cornice likely failed and started D2.5 avalanche in heavily wind loaded location. |
|
Snowpack Observations
Objective to target faceted layer around 100cms deep. Facets appear to be rounding well deep in the snowpack. The layer did not react in compression or extended column tests. Propagation Saw Test Test showed propagation on layer is likely with saw propagation reaching 50cms into 100cm block. PST50/100 end down 100cms on 211205 layer.
Avalanche Problems
| Problem | Location | Distribution | Sensitivity | Size | Comments |
|---|---|---|---|---|---|
Wind Slab
|
|
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Persistent Slab
|
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Layer Depth/Date: 100cm deep / 12-22-2021 PST50/100 End down 100cm on 211205 layer |
- Wind slabs on leeward sides of ridgelines above 7500 feet.
- Watch persistent slab on northerly slopes if rapid warming or heavy load arrives.