Storm Slabs on Grant Ridge

Location Name: 
Forecaster Observation - Grant Ridge
Observation date: 
Tuesday, February 12, 2019 - 17:30
Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Location

Tabs

Quick Observation

We went up Grant Ridge in the Middle Fork looking for in-storm, and persistent instabilities. We found both to be reactive with the new loading.

  • Instabilities were widespread, especially where southwest winds had drifted the new snow. Shooting cracks and small avalanches triggered from test slopes were common on easterly aspects and middle and upper elevations. We got several, small, remotely triggered test slope results from over 100' away. Many of these results failed as the newer, denser, snow  above the low-density snow from earlier this week - about 6-10" deep. But, several of our more impressive results failed in facets above the 2/2 crust. These failures were between 18" and 2' deep. We triggered a storm slab on a small breakover on our descent.
  • At lower elevations, where the trees are dense and conditions are still "low-tide" in this area, we saw mostly shallow sluffing.
  • We stuck to low-angled, sheltered slopes far back from easterly aspects where we saw the most wind drifting.
Snowpack, Avalanche, Weather Images: 
Snowpack, Avalanche, Weather Videos: 

2/12/19 - Touchy Storm Slabs on Grant Ridge

Travel Details
Region: 
Flathead Range - Middle Fork Corridor
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
W
NW
Red Flags: 
Shooting cracks
Collapsing / whumpfing noises
Blowing snow
Persistent Weak Layers: 
Facets or Faceted Crust
Buried
New Snow in the past 24 hours: 
9.00in.
Total Snow Depth: 
120cm
More comments about the snowpack and weather: 
@ 4850' NW aspect: HS = 95cm ECTN 9 and CT3 SP down 23cm at the new/old interface (new snow denser than old), 2/2 Cr down 46cm, CT5 SC down 50cm in FCs under the 2/2 Cr, under the 2/2 Cr the snowpack was a sandwich of crusts and facets. @ 5400' NE aspect: HS = 115cm, ECTPE x2 down 15cm at the old/new (same density change), 2/2 Cr down 42cm (2 crusts with facets above/below/between). Possibly false stable results at these 2 locations because we got clear whumpfing and shooting cracks breaking down on facets about the 2/2 crust up to ~6200'. The difference was that at our test locations there had been no wind affect, whereas the other locations had clear drifting. 3 more inches of snow fell between leaving the truck at 930am and getting back to the trailhead at 330pm.
Blowing Snow: 
Moderate
Wind Speed: 
Moderate (Small trees sway)
Wind Direction: 
Southwest
Air temperature: 
Below Freezing
Snow line: 
Below Canyon Floor
Sky Cover: 
Overcast (OVC)
Highest Precipitation Rate: 
Moderate Snowfall (S2)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Tuesday, February 12, 2019 - 14:45
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
Hide Trigger
Trigger: 
skier
Trigger Modifier: 
Accidentally Triggered
Hide Terrain
Start Zone Slope Angle: 
35
Aspect: 
Northeast
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): 
40ft.
Avalanche Width (Average width): 
50ft.
Avalanche Location: