Zone: Northwest Mountains

Location: Anthracites

Date of Observation: 12/11/2020

Name: Eric Murrow

Subject: Kebler Pass ski

Aspect: North, North East, East

Elevation: 10,000 – 11,500

Avalanches:

Intentionally triggered one dry loose avalanche that quickly gouged into old snow. Slope was small, but debris volume was bigger than you would expect with only 5 inches of new snow.

Weather: Overcast skies, consistent light snowfall with several short periods of moderate snowfall (S-1 to S2), and generally light winds with occasional moderate gusts from westerly directions.

Snowpack: New snow at Kebler Pass/Antracites was 4″ at 10am and reached 6″ by 3pm. Relatively low-density snowfall. Intentionally sought out terrain features without previous traffic and found loose avalanches were easy to trigger in the new snow that quickly gouged around 6 to 8 inches into old surface (see photo). While hunting for drifted areas was able to produce some cracking to the old snow interface, but propagation was no more than 10 feet and cracks only 6 inches deep. By 230 pm snow surfaces in open north-facing terrain showed more signs of cracking but only shot a ski length in front of you.

Photos:

Zone: Northwest Mountains

Location: The Deep Slate

Date of Observation: 12/11/2020

Name: J B

Subject: 20201211 Storm Obs

Aspect: North East, East

Elevation: 9400-11400

Avalanches:

Innumerable remote, natural, and ski cut triggered D1 avalanches within the storm slab. Crowns broke down to the old snow, but primarily slumped and stayed in place with the exception of the top 5-10 cms of new snow which did not run far. Avalanches were concentrated to convex rolls over 38 degrees. The largest slide was triggered by a ski cut near rocks on an old bed surface and piled up enough snow on the uphill side of trees to bury someone to their waist but would not have ended their days- larger D1 with a crown of 70m wide and 40cms deep (SS-AS-R2-D1+-I).

Weather: Steady snowfall 2-3cms/hour from 10am to 2pm. Clearing up around 2pm. Light winds. No observable wind transport of new snow or solar effect. Felt cold, 20 F?

Snowpack: 45 cms of new snow by 2pm!! That’s a foot and a half for you imperial goons. The new snow doubled the existing snow depth in spots. Old snow interfaces were a mixture of sun crust on E-S aspects and faceted dry shallow on anything with a hint of North to it.

Photos:

Zone: Northwest Mountains
Location: Skylkill Ridge
Date of Observation: 12/11/2020
Name: Evan Ross

Aspect: North East
Elevation: 9,200 to 11,200

Avalanches: Natural avalanche activity spiked mid-day during a period of heavy snowfall. Soft slabs of new snow failing on the very weak, faceted, old snow. Many D1’s near treeline and a few D1’s below treeline. About five D2’s and, one D2.5 near treeline. For the most part, these were very soft slabs that just slumped into the weak facets below, started moving, then stopped 50 to 100ft downhill. Others initiated the same way, but continued to gain momentum and entrain the full snowpack.

Not all these slabs propagated widely, but there were some standouts. Runaway Ski propagated across most of its start zone and continued all the way across Thanksgiving. Runaway Ski mostly just slumped and was D1 in size. While Thanksgiving ran nearly wall to wall and hit the bench. Even the skiers left shoulder in Runaway pulled 90% of that terrain feature.

Yogy’s had a soft slab propagate across 80% of its start zone. The skier’s right side mostly slummed and continued to run about 1/2 way to the bench as a D1.5. While the skier’s left side quickly entrained the full snowpack, and was estimated to be D2 in size, I couldn’t see how far the skier’s left side ran given poor vis.

The crown lines on these avalanches were already getting hard to see from a distance given their soft slumpy character, and the 15-30cm crowns were filling back in.

Weather: Fairly consistent snowfall from the time I headed out at 9:30am until 2:30pm. Mostly S1 to S2 with a period mid-day near S5. Mostly light winds at ridgeline, drifting snow during brief periods of moderate gusts.

Snowpack: The avalanche danger increased quickly sometime around 11am to 1pm. During the morning, test slopes were collapsing and shooting cracks up to about 15ft. As the day progressed that activity increased and many small avalanches were remotely triggered up to a couple hundred feet away. For the remote triggers that were further away I think it was an interesting chain of events with one small slab beginning to move, then sympathetically triggering another further away, and another… All the avalanche activity was silent and I never felt a collapse.

The entire snowpack was mostly unsupportive to skis making for scary downhill travel with all the hidden ground hazards. HS generally averaged 40 to 50cm’s down low and 80 to 90cm’s closer to 11,000ft.

HN was about 30cm at 11,000ft and 25cm’s in the valley bottom at 9,200ft.