Marion Lake obs

Location Name: Forecaster Observation - Essex Mountain, Flathead Range Observation date: Sunday, December 24, 2017 - 13:15	Is this an Avalanche Observation: No

Observation made by: Forecaster

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Quick Observation

Pockets of surface hoar near ridgelines and small grained near surface facts forming at the surface.
Extensive avalanche activity from the 12/19 cycle. We traveled along Essex Mtn Ridgeline and nearly all paths on either side of the ridge had run, evidenced by visible crown lines, debris, and/or feeling the snow depth down to the Thanksgiving crust.
No signs of recent wind slab formation along this ridgeline. Calm winds and no blowing snow on the peaks.
No collapses or cracking on steep or low angle terrain. Minor sluffing on steep slopes. The snowpack structure is variable across steep terrain due to previous avalanches: anywhere from 6" over the Thanksgiving crust up to 30" over lingering facets above the crust.
One pit in an area that hadn't avalanched had propagating, sudden collapse failure under moderate initiation, 90 cm deep on 4F- facets on the ground.

Snowpack, Avalanche, Weather Images:

Travel Details

Region:

Flathead Range - Bob Marshall Wilderness

Route Description:

Up to Marion Lake and the NW side of Essex Mtn

Activity:

Skiing

Snowpack Details

Snowpack and Weather Details:

Terrain

Elevation of observation:

5000-6500 ft

Above 6500 ft

Aspect(s) of observation:

Persistent Weak Layers:

On the surface

Buried

New Snow in the past 24 hours:

0.00in.

Total Snow Depth:

100-120 cm

Avalanche Details

Avalanche Details:

Date and Time of Avalanche:

Tuesday, December 19, 2017 - 18:15

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

Old snow

More information or comments about the avalanche:

All aspects and elevations. Up to at least D2.5 in size

Trigger

Trigger:

natural

Size

Destructive Size:

D2 Could bury, injure, or kill a person.

Relative Size:

R3 Medium

Avalanche Location:

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