Febru-buried

Location Name: 
Forecaster Observation - Skyland
Observation date: 
Sunday, February 16, 2020 - 17:30
Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Tabs

Quick Observation

Automated weather stations near Marias Pass have reported 8-20" change in snow height in the past 48 hours. We went to see of they were accurate. 

  • We found 5-7 inches of snow from the past few days. Snow showers today put down another 2-4". However, 1-3 feet of snow has accumulated above the 2/1 crust. 
  • Gusty winds this morning were blowing snow from trees at mid elevations but not building drifts.
  • We avoided being on slopes under large, overhanging cornices on the ridgeline.
  • One large natural avalanche ran on a leeward, upper elevation slope early afternoon (image and avalanche tab).
  • The few cornices we tested were fragile, releasing fridge- and sofa-sized chunks with just a couple of kicks. These only produced sluffs in the fresh snow on the slopes below.
  • A snow profile on a mid-elevation, easterly slope showed about 3 feet of consolidating snow above the 2/1 crust. Tests produced no propagation or sudden failures in this snow or the snow immediately above and below the 2/1 crust. The 2/1 crust is buried 1-2 feet below about 6000 feet.
  • Near ridges (~7000 ft), we found an 8-12" thick, hard (4F+ to 1F) wind slab below the fresh snow. This slab did not extend far down the slope. I suspect slabs would be thicker and wider in  more exposed leeward terrain several hundred feet higher.

We avoided steep slopes near and below the ridgeline, and skied steep slopes with no evidence of wind loading one at a time. 

Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Flathead Range - Marias Pass/Skyland
Activity: 
Skiing
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
E
SE
Red Flags: 
More than a foot of new snow or heavy snowfall rates (>1"/hr)
Blowing snow
Persistent Weak Layers: 
Not observed
New Snow in the past 24 hours: 
9.00in.
Total Snow Depth: 
260 cm
More comments about the snowpack and weather: 
Snow showers - heavy (S5) at times - alternating with broken skies. L-M winds, gusty, with some snow-nados in AM as last night's snow blew off trees. Profile at 6400 feet, E facing slope, HS 260 cm. 85 cm progressively consolidated recent snow (Fist to 1F) above the 2/1 crust (deteriorated to 1F). No facets visible in loupe above or below crust. ECTX on and immediately below crust. ECTN H and CTH Resistant Planar 65 cm below surface. No other distinct weak layers or interfaces above 2/1. Below about Cascadilla, temps at road level 32* on drive home. Snow gone from trees on S facing slopes and snow at road level appeared to have gotten moist or wet.
Blowing Snow: 
Moderate
Wind Speed: 
Moderate (Small trees sway)
Wind Direction: 
Southwest
Air temperature: 
Below Freezing
Snow line: 
3400
Sky Cover: 
Obscured by fog, etc (X)
Highest Precipitation Rate: 
Heavy Snowfall (S5)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Sunday, February 16, 2020 - 14:00
Number of avalanches: 
1
Avalanche Type: 
Unknown
Failure Plane/Weak Layer: 
Unknown
More information or comments about the avalanche: 

Didn't see crown on late morning ride in, though light flat. Obvious mid-afternoon. Possibly triggered by falling cornice or sluff through rocks above. Crown distinct; likely several feet deep. Probably wind-drifted snow. 

Hide Trigger
Trigger: 
natural
Trigger Modifier: 
Cornice Fall Triggered
Hide Terrain
Start Zone Slope Angle: 
39
Aspect: 
East
Starting Elevation: 
7300
Hide Size
Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R2 Small
Crown Height: 
3 ft
Avalanche Length (Vertical Run): 
750ft.
Avalanche Width (Average width): 
150ft.
Avalanche Location: