Observation: Summit

Location: Fresno

Date:

February 2, 2021 3:00pm

Observer:

Johnston-Bloom / Schauer Forecaster

Route & General Observations

Standard uptrack to 2900′ to get a general sense of surface conditions, wind-loading from the NW wind event, depth of recent snow, inventory of the buried surface hoar and near surface facet layers.

Road obs to Summit Lake lodge to get eyes on the natural wind triggered avalanches on Colorado reported yesterday – see Nancy’s ob.

Layers of note:

1.28 buried surface hoar and/or near surface facets

1.23 and or 1.18 near surface facets down 20 cm – 50 cm

Red Flags

Red flags are simple visual clues that are a sign of potential avalanche danger. Please record any sign of red flags below.

Obvious signs of instability

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

Observer Comments

Two natural avalanches on Colorado peak that were wind triggered yesterday.
Small wind slab crowns on Fresno
Cracking on small wind loaded slopes

Weather & Snow Characteristics

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

Weather

Overcast
Teens at upper elevations
Single digits at the truck
Calm

Snow surface

Surface hoar over 2-3" of near surface facets up to where wind effect was evident around 2600'. Degrading melt-freeze crust up to 1400' below the 2-3" of snow.
Variable wind effect to high point at 2900' thin wind skin transitioning to wind board and 6-8" wind slab.
Lots of scouring and cross-loading observed in the alpine.

Snowpack

We dug at 2230' see Snowpilot profile for Pit # 1. Did not dig to the ground in this pit.
Pit#2, HS: 135 cm, E aspect, 31° slope. The most recent snow from 1.28/1.29 has surface hoar at the top and is faceting. This snow fell on another layer of surface hoar (10 cm down) and near surface facets. Below this is a layer of decomposing precip particles. 20 cm down there is a layer small facets (1mm). CT 12, CT 13 and ECTP 13 on this layer. 50 cm down there was another layer of small facets (.5-1mm), CT 26, CT 27. ECTX. The 12.1 crust sandwich was 80 cm down with a layer of faceted snow in the middle. No test results in this layer but it was easy to identify and pry the column off here. Pit to the ground. Basal facets were moist and rounding.

We dug at 2700' in a wind-loaded spot to look at wind-loading over the weak layers. We did not see any buried surface hoar in this pit. We did not dig to the ground. There was a slight drop just before hitting ground while probing indicating the presence of basal facets.

Pit #1 HS: 255 cm, pit depth 100 cm, S aspect, 21° slope. Under a 15 cm sandwich of wind crusts there was a thin layer of small facets (1mm), CT6, CT13, ECTN12. The was another layer of small facets (.5-1mm) 35 cm down, CT23, CT25, ECTX. There was pencil hard snow below this for the remainder of the pit.
Pit # 2, HS: 185 cm, CT12Q2 (x2), ECTN15 down 10 cm on small facets, CT23, CT26 down 35 cm on small facets.

Skinning to our high point around 2900' we encountered small shooting cracks and small slabs on wind-loaded rolls failing on the recently buried near surface facets. Skiing down at 2400' there was one small steep section where a 2-4" pocket slid on buried surface hoar.

Photos & Video

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