Little Slabby, Little Sluffy

Location Name: 
Forecaster Observation: Southern Glacier Park
Observation date: 
Tuesday, February 25, 2020 - 17:15

Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Tabs

Quick Observation

Went to the John Stevens Canyon area hunting wind slabs and sluffs. It wasn't supper windy and it wasn't the most new storm snow, but it was a little slabby and a little sluffy to be sure.

  • We found between 6 and 10 inches of new, low density snow sitting on top of old wind slabs, melt freeze crusts, and settled old snow depending on the aspect. We did not find surface hoar or facets at the 2/23 storm interface.
  • At middle and upper elevations the new snow sluffed readily on test slopes steeper than 40 degrees. Slopes where I usually test for wind slabs at these elevations did not produce anything but sluffs, though I did get a few small cornices to break off and cause sluffing on the slopes below.
  • West winds were light, at best, into the early afternoon. But as the day went on, and as we climbed above 6500 feet, we saw moderate blowing snow from alpine ridges. Light to moderate wind was enough to move the very low density snow onto leeward slopes. Gusts produced occasional snow banners from nearby peaks. On our descent we saw blowing snow on favored middle elevation slopes, but it hadn't been moving snow for very long and we couldn't find more than a thin wind skin on the surface.
  • Cornices and wind slabs were reactive on alpine test slopes. These were small - slabs 2-10 inches and cornices up to 2 feet thick, but they cracked with very little effort. Slabs were soft and broke on even softer storm snow below. 
  • We avoided slopes under corniced ridgelines and very steep, confined gullies where we wouldn't be able to manage our sluffs. With those caveats, the new snow skied great until we got to lower elevations where it was just becoming moist on south-facing slopes by 2:30.
Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Glacier National Park - Southern Lewis Range
Route Description: 

To 7000'

Activity: 
Skiing
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
Red Flags: 
Blowing snow
Persistent Weak Layers: 
Facets or Faceted Crust
Buried
New Snow in the past 24 hours: 
10.00in.
Total Snow Depth: 
185cm
More comments about the snowpack and weather: 
Breaks of blue sky and periods of light snow. Sometimes both at the same time. Winds were only notable on alpine ridges. Many quick test pits on sheltered slopes and northerly aspects looking for surface hoar - didn't find it. The weakest snow we found was F hard 4mm depth hoar in a very shallow area under about 2 feet of 4F snow. Total snow depth here was about 3 feet - SE aspect at 6000'. My guess is that it constantly gets scoured by the typical W winds and the snowpack stays shallow here with a high temperature gradient.
Blowing Snow: 
Moderate
Wind Speed: 
Moderate (Small trees sway)
Wind Direction: 
West
Air temperature: 
Below Freezing
Snow line: 
canyon floor
Sky Cover: 
Mostly Cloudy (BRK)
Highest Precipitation Rate: 
Very Light Snowfall (S-1)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Tuesday, February 25, 2020 - 13:00
Number of avalanches: 
4
Avalanche Type: 
Loose Dry/ Sluff
Failure Plane/Weak Layer: 
Within storm snow
More information or comments about the avalanche: 
Hide Trigger
Trigger: 
skier
Trigger Modifier: 
Intentionally Triggered
Hide Terrain
Start Zone Slope Angle: 
50
Aspect: 
East
Starting Elevation: 
near-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R1 Very Small
Crown Height: 
Less than 1 ft
Avalanche Length (Vertical Run): 
25ft.
Avalanche Width (Average width): 
6ft.
Avalanche Location: 
Date and Time of Avalanche: 
Tuesday, February 25, 2020 - 13:30
Number of avalanches: 
3
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
Within storm snow
More information or comments about the avalanche: 
Hide Trigger
Trigger: 
skier
Trigger Modifier: 
Intentionally Triggered
Hide Terrain
Start Zone Slope Angle: 
35
Aspect: 
Northeast
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R1 Very Small
Crown Height: 
Less than 1 ft
Avalanche Length (Vertical Run): 
50ft.
Avalanche Width (Average width): 
30ft.
Avalanche Location: