Avalanche: Hatcher Pass

Location: Divide Ridge

Date:

March 3, 2021 6:38pm

Observer:

Allie Barker Forecaster

Route & General Observations

Toured up Divide Ridge (lower part of Idaho Peak) to assess stability on south aspects and do a crown profile on the 3/2 snomachine triggered slab avalanche. Numerous dry loose naturals were observed, mostly from 3/1-3/2. 4″ of new snow on crust conditions persist in most locations under 4000′.

Avalanche Details

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Trigger	Snowmachiner	Remote Trigger	Unknown
Avalanche Type	Hard Slab	Aspect	West
Elevation	2700ft	Slope Angle	40deg
Crown Depth	3ft	Width	90ft
Vertical Run	400ft

Avalanche Details

Snowmachiner was high-marking and triggered an avalanche. See original obs from Brandon.
HS-AM-D2-O
HS 140 cm
Failed on 2mm chained facets sitting on Jan 6 wind slab
Crown depth 2 to 3 feet
Debris was 1-5 feet deep

Red Flags

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Obvious signs of instability

Recent Avalanches?	Yes
Collapsing (Whumphing)?	No
Cracking (Shooting cracks)?	No

Observer Comments

3/3 Numerous dry loose avalanches (sluffs) mostly small and a few large
3/2 Snogo triggered persistent slab avy on W face of lower Divide Ridge.

Weather & Snow Characteristics

Please provide details to help us determine the weather and snowpack during the time this observation took place.

Weather

4" new snow on 2/27 with minimal wind G20 for 3 hrs. Wind info can not be verified due to lack of data from weather instruments.
Temps:
10am 10degF @ 3505'
2pm 16degF @3505'

Snow surface

4" of new snow, PP and NSF sitting on a very interesting drizzle crust that formed before and after the last storm. The temps were never above freezing during the storm.
The freezing drizzle event was driven by a warm cloud processes. The key is having a balance between the stability, wind flow, in a moist layer, while keeping the cloud in the 0 to -10C temp range. Its technical...NWS couldn't figure it out and either can we.

Snowpack

Crown profile of Divide Ridge Avalanche
W aspect 40deg slope 2700' elevation
HS 115
115-94 DF
95-94 Drizzle crust
94-70 4F to F DF
70-66 F Facets rounding
66-40 1F rounds
40-20 4F facets
20-15 F chained facets * avalanche failed at 15 cm
*weak layer was 3-4 cm chained facets sitting on top of old wind slab
15-10 P wind slab
10-0 rounds faceting

2nd pit on south aspect- see pit profile

Photos & Video

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