Recent avalanches on Great Northern

Location Name: 
Great Northern
Region: 
Flathead Range/Glacier National Park - Middle Fork Corridor
Date and time of avalanche (best estimate if unknown): 
Thu, 11/09/2017 - 22:00
Location Map: 


Red Flags: 
Recent avalanche activity
Recent loading by new snow, wind, or rain
Obvious avalanche path
Terrain Trap

Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
Slab
Trigger type: 
Natural
Crown Height: 
Less than 1 ft
Aspect: 
Northeast
Weak Layer: 
New/old snow interface
Terrain: 
Above Treeline
Elevation: 
7 500ft.
Number of similar avalanches: 
5
Number of people caught: 
0
More detailed information about the avalanche: 

Wet or moist snowpack up to 5,500 feet, less than 30 cm thick, homogenous, and no avalanche concerns.  Above 5,500 feet, the snowpack was dry and averaged about 50 cm thick.  In the terrain that we traveled on, we found a uniform snowpack with no obvious weak layers on south and west aspects up to 7,000 ft.  On NW to NE aspects, basal crust/facet layers prevail, buried by slabs ranging from 0 to 70 cm thick, depending on windloading patterns from predominately NE winds.  Basal facets were generally weaker (Fist or 4F) and larger grained (1.0 mm) below the Halloween crust, and we found a mix of rounds or rounding facets (<.5mm, 4F- to 1F) above the crust.  Neither layers were reactive in stability tests conducted at two different locations (See profiles).  In a crossloaded gulley, we found up to 12cm of dense, freshly drifted snow and initiated phonebook-sized cracks underfoot.   We steered away from suspect windloaded features.

We observed about 5 natural soft slab avalanches that likely ran Thursday or Friday, on windloaded NE aspects above treeline.  These likely ran on Thursday's storm interface, estimated 6-12" deep, and produced D1 to D1.5 debris piles (SS-N-R2-D1.5-I).   One of these shallower slabs stepped stepped down to the ground on a rock slab, about 2 feet deep and produced a larger debris pile (SS-N-R2-D2-G).

Snowpit or crown profile photo or graph: 
Avalanche Photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Moderate
Precipitation: 
None
Air temperature trend: 
Static
Wind Direction: 
Southwest
Accumulation rate: 
None
Activity: 
Skiing