New snow instabilities on Grant Ridge

Location Name: 
Forecaster Observation- Grant Ridge, Flathead Range
Observation date: 
Monday, April 2, 2018 - 19:15
Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Tabs

Quick Observation
  • 6” to 10” of low-density new snow was poorly bonded to underlying rain or sun crust at all elevations.
  • We triggered numerous sluffs at mid and low elevations and numerous D1 soft slabs above 6,000 ft. There was just enough previous wind transport to form reactive slabs in wind affected terrain, up to 1 foot deep.
  • There was a small loose dry and soft slab cycle last night at all elevations, mostly D1 but a few D1.5 to D2s a few hundred feet wide. These all failed at the storm interface near previous surface crusts. 
  • We produced minor cracking in most slopes and a few shooting cracks in leeward terrain.
  • Light snow all afternoon. Calm winds, signs of earlier southwest wind transport.  Unseasonably cold temps. 
Snowpack, Avalanche, Weather Images: 
Snowpack, Avalanche, Weather Videos: 

April 2, 2018. New snow instabilities in the Flathead Range

Travel Details
Region: 
Flathead Range - Middle Fork Corridor
Route Description: 

Grant Ridge 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: 
NE
E
SE
S
Red Flags: 
Shooting cracks
Persistent Weak Layers: 
Buried
New Snow in the past 24 hours: 
8.00in.
More comments about the snowpack and weather: 
6" at 5,000 feet. 8-12" with previous light wind transport above 6,000'. Low density (~8%) The snow was equally reactive on all aspects, but fell on sun crust on southerly, rain crust below ~6,000' on northerly and dense wind affected snow (DFs/rounds) over a rain crust from 6k to 7k. Seemed like you needed just a hint of windloading to trigger a slab today. ECTX results in the soft slab. The rain crust at higher elevations is friable and has facets below it. Could be a problem with a large load. On southerlies, there is a thin sun crust/thick sun crust sandwich below the new snow with DFs between.
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Sunday, April 1, 2018 - 23:30
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
More information or comments about the avalanche: 

All elevation bands and aspects, mostly D1, a few D1.5 or D2.   

Hide Trigger
Trigger: 
natural
Hide Size
Destructive Size: 
D1.5
Relative Size: 
R1 Very Small
Crown Height: 
Less than 1 ft
Avalanche Width (Average width): 
50ft.
Avalanche Location: 
Date and Time of Avalanche: 
Monday, April 2, 2018 - 14:45
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
Hide Trigger
Trigger: 
skier
Trigger Modifier: 
Intentionally Triggered
Hide Terrain
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 Width (Average width): 
50ft.
Hide People Involved
Number of people caught: 
0
Avalanche Location: 
Date and Time of Avalanche: 
Monday, April 2, 2018 - 14:45
Avalanche Type: 
Loose Dry/ Sluff
Failure Plane/Weak Layer: 
Within storm snow
More information or comments about the avalanche: 

Natural loose dry ran last night. Numerous skier triggered loose dry today.  All aspects, mostly below 6,000'

Hide Trigger
Trigger: 
skier
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Crown Height: 
Less than 1 ft
Avalanche Location: