Warning Signs O'Plenty

Location Name: Forecaster Observation: Southern Glacier Park Observation date: Tuesday, February 23, 2021 - 18:45	Is this an Avalanche Observation: Yes

Observation made by: Forecaster

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Quick Observation

The southeast corner of the forecast area received some of the most new snow and some of the strongest winds of the storm.

We experienced several audible collapses at lower elevations in sheltered terrain.
We got shooting cracks and triggered small slabs of drifted snow on leeward aspects at middle elevations.
With a little cornice drop we triggered a large hard slab avalanche that broke 2.5 feet deep and propagated 100 feet wide. It failed in facets and ran on the mid-January crust. More info in the avalanche tab.
We did not see any natural avalanches, but there was poor visibility from snow showers and blowing snow, which were both widespread and frequently intense.
More info about the weather and snowpack in that tab.

We traveled on a ridgeline with slope angles less than 30 degrees and no overhead hazards.

Snowpack, Avalanche, Weather Images:

Snowpack, Avalanche, Weather Videos:

2/23/21 Instability O'Plenty

Travel Details

Region:

Glacier National Park - Southern Lewis Range

Activity:

Skiing

Snowpack Details

Snowpack and Weather Details:

Terrain

Elevation of observation:

3500-5000 ft

5000-6500 ft

Above 6500 ft

Aspect(s) of observation:

Red Flags:

Avalanches from the past 2 days

Shooting cracks

Collapsing / whumpfing noises

More than a foot of new snow or heavy snowfall rates (>1"/hr)

Blowing snow

Persistent Weak Layers:

Facets or Faceted Crust

Buried

New Snow in the past 24 hours:

10.00in.

Total Snow Depth:

200cm

More comments about the snowpack and weather:

Below 5,000': new snow = 5" of dry grauple over water-saturated, weak, old snow to the mid-Jan crust. Above 5,000': new snow = 10-16" of dry F hard DFs, graupel, and 4F wind drifts over settled 4F or older wind blown 1F-P drifts, snowpack dry. @6800' on NE aspect where HS = 205 cm: ECTP12 down 43 on small facets above an older, 1F wind board; 1/13 cr down 85 with 4F large facets above and below. Lots of blowing snow at all elevations. Showers from light to heavy snowfall all day broken by oh-so-brief peaks of blue sky. Mostly poor visibility. Snowfall cleared with BKN cloud cover north of Stanton Lake on the drive back. Still blowing snow in the Middle Fork and GNP despite the end to showers this afternoon.

Blowing Snow:

Moderate

Wind Speed:

Moderate (Small trees sway)

Wind Direction:

Southwest

Air temperature:

Below Freezing

Snow line:

canyon floor

Sky Cover:

Mostly Cloudy (BRK)

Highest Precipitation Rate:

Heavy Snowfall (S5)

Avalanche Details

Avalanche Details:

Date and Time of Avalanche:

Tuesday, February 23, 2021 - 11:30

Number of avalanches:

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

Wind drifted snow. Slab = 4F over F hard graupel.

Trigger

Trigger:

skier

Trigger Modifier:

Intentionally Triggered

Terrain

Start Zone Slope Angle:

Aspect:

East

Starting Elevation:

near-treeline

Size

Destructive Size:

D1 Relatively harmless to people.

Relative Size:

R2 Small

Crown Height:

Less than 1 ft

Avalanche Length (Vertical Run):

30ft.

Avalanche Width (Average width):

40ft.

Avalanche Location:

Date and Time of Avalanche:

Tuesday, February 23, 2021 - 13:45

Number of avalanches:

Avalanche Type:

Hard Slab

Failure Plane/Weak Layer:

Old snow

More information or comments about the avalanche:

Triggered with a small cornice drop. Average crown depth 2.5 feet. Failed on facets above the 1/13 crust. Slab = 1F.

Trigger

Trigger:

skier

Trigger Modifier:

Intentionally Triggered

Terrain

Start Zone Slope Angle:

Aspect:

East

Starting Elevation:

near-treeline

Size

Destructive Size:

D2 Could bury, injure, or kill a person.

Relative Size:

R3 Medium

Crown Height:

3 ft

Avalanche Length (Vertical Run):

350ft.

Avalanche Width (Average width):

100ft.

Avalanche Location:

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