Not quite 10 in Ten Lakes

Location Name: 
Forecaster Observation - Ten Lakes
Observation date: 
Tuesday, February 23, 2021 - 18:00
Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Location

Tabs

Quick Observation

Ten Lakes/ Grave Creek explore today, to look for recent avalanche activity and assess recently-developed avalanche problems. 

  • Spotted 4 small slabs that released naturally on very steep (~40*) easterly slopes. The terrain for these slides looked to be either cross-loaded or top-loaded by westerly winds.
  • There were likely more similar slides; visibility wasn't great and we didn't have good vantage points when the visibility improved.
  • We found 4-6 inches of fresh snow in most loactions, with 8 inches in a few spots, possibly from drifting. The most recent snow was dry, and consists of heavily rimed particles and graupel, so it's not very cohesive.
  • Low clouds in the morning gave way to convective showers  (S1-5, mostly rimed particles or graupel) by early afternoon. 
  • We some some blowing snow near ridges and a few soft drifts in exposed spots in open trees. 
  • We felt no collapses and saw no cracking, though much of the terrain where we were was well-traveled this weekend. 
  • The large west and southwest facing slide paths in upper Grave Creek do not appear to have run during this winter's natural avalanche cycles.
  • The snowpack below about 4500 feet is moist to wet below a refrozen surface. 

The loose fresh snow made for some fine riding up high. 

Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Whitefish Range - Northern (north of Coal Creek)
Route Description: 

Ten Lakes/ Grave Creek area to 6600 feet.

Activity: 
Snowmobiling
Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
3500-5000 ft
5000-6500 ft
Above 6500 ft
Aspect(s) of observation: 
N
NE
E
SE
S
SW
W
NW
Red Flags: 
Avalanches from the past 2 days
More than a foot of new snow or heavy snowfall rates (>1"/hr)
Persistent Weak Layers: 
Surface Hoar
Facets or Faceted Crust
Buried
New Snow in the past 24 hours: 
6.00in.
More comments about the snowpack and weather: 
1-7" fresh snow, increasing with elevation. with convective showers - heavy at times - alternating w patches of blue skies. Test profile at 5700 ft, NW aspect: 1/13 MFcr down 65 cm. Snow above surprisingly unconsolidated (F-4F+ hard), with recently buried surface hoar 15-18 cm < surface. CTE/CTM SP. No propagation in ECTs. Most pronounced weak layers above and below crust. Poorly-preserved surface hoar 2-3 cm above crust; soft, fine-grained facets immediately below. Crust still K hard at top. ECTN 28 or 30+ on these layers, though they'd show up as distinct interfaces when prying on columns.
Blowing Snow: 
Light
Wind Speed: 
Moderate (Small trees sway)
Wind Direction: 
West
Air temperature: 
Below Freezing
Snow line: 
valley floor
Sky Cover: 
Decreasing Clouds
Highest Precipitation Rate: 
Heavy Snowfall (S5)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Tuesday, February 23, 2021 - 05:45
Number of avalanches: 
4
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
Unknown
More information or comments about the avalanche: 

Small slabs on very steep, easterly slopes that were likely top-loaded or cross-loaded by strong winds. Only 1 appeared to be right at a ridgeline; others all well down slope. 

Hide Trigger
Trigger: 
natural
Hide Terrain
Aspect: 
East
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D1.5
Relative Size: 
R2 Small
Crown Height: 
1 ft
Avalanche Width (Average width): 
45ft.
Avalanche Location: