Storm slab cycle in Noisy Basin

Location Name: 
Forecaster Observation - Noisy Basin, Swan Range
Observation date: 
Saturday, February 16, 2019 - 14:00
Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Tabs

Quick Observation

This morning the Noisy Basin SNOTEL reported 1.5" of Snow Water Equivalent (SWE) in the past 24 hours. We traveled to the Swan Range to see the effect this heavy snowfall had on our snowpack.

  • A widespread storm slab avalanche cycle occurred late last night or early this morning (February 16) mid-storm. Numerous slides were noted on the east side of the ridgeline between "Checkerboard" and where the ridge turns and heads east to the Mt Aeneas Ridge. Resultant debris was rated as D2 which could bury, injure or kill a person.
  • Visibility was poor but we feel that this storm slab cycle was extensive in the Noisy Basin/Jewel Basin area.
  • Overnight snow totals varied between 14" @ 4100' and 18" @6200'.
  • Instabilities included collapsing, cracking and shooting cracks. Cornices were tender and reactive to the weight of a skier.
Snowpack, Avalanche, Weather Images: 
Snowpack, Avalanche, Weather Videos: 

February 16, 2019 - Instabilities in the Swan Range

Travel Details
Region: 
Swan Range - West Side (Flathead Valley access)
Route Description: 

The Switchback trail.

Activity: 
Skiing
Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
3500-5000 ft
5000-6500 ft
Aspect(s) of observation: 
NE
E
SW
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: 
18.00in.
Total Snow Depth: 
110"
More comments about the snowpack and weather: 
Snowpit @ 6000': HS=110" Propagation within the storm slab ECTP @ 6 16" down. The 2/2 crust is buried approximately 5' deep at this location and was unreactive in stability tests.
Blowing Snow: 
Light
Wind Speed: 
Light (Twigs in motion)
Wind Direction: 
Southwest
Air temperature: 
Below Freezing
Snow line: 
1000'
Sky Cover: 
Obscured by fog, etc (X)
Highest Precipitation Rate: 
Heavy Snowfall (S5)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Saturday, February 16, 2019 - 01:00
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
Within storm snow
More information or comments about the avalanche: 

All slides we noted occurred on wind loaded mid-elevation slopes within 100' vertical feet of the ridgeline. Poor visibility prevented us from viewing other terrain.

Hide Trigger
Trigger: 
natural
Hide Terrain
Start Zone Slope Angle: 
35
Aspect: 
East
Starting Elevation: 
5900' - 6400'
Hide Size
Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R3 Medium
Crown Height: 
1 ft
Avalanche Length (Vertical Run): 
400ft.
Avalanche Width (Average width): 
100ft.
Avalanche Location: