Sugar Shack

CBAC 2020-21 Observations

Date of Observation: 01/17/2021
Name: Zach Guy

Zone: Northwest Mountains
Location: East Beckwith
Aspect: East
Elevation: 10,000 – 11,600′

Avalanches: None
Weather: Light northwest winds. Partly to mostly cloudy.
Snowpack: We traveled on several steep east facing slopes near and above treeline without signs of instability. A lot of ski pole probing easily going to the ground indicated the persistent slab structure was mostly faceted away. We dug a test pit in a concave part of the bowl holding a deeper, denser snowpack. Despite an unnerving looking structure (see photo), tests produced non-propagating results. We chose to avoid this part of the bowl, regardless.
Last week’s winds did little to damage the weak snow surface here, apart from forming a thin windcrust above the facets at higher elevations. All elevations that we traveled on have a persistent weak layer continuous across the terrain (1-1.5mm, Fist hard). Meltfreeze crusts are on anything with a hint of south and grow thicker with southerly tilt. See photos and captions for details.

 

Photos:

wind slab hunters

CBAC 2020-21 Observations

Date of Observation: 01/16/2021
Name: Zach Guy

Zone: Southeast Mountains
Location: Various valley locations near Crested Butte
Aspect: North East
Elevation: 8900-9200′

Avalanches: None
Snowpack: We targeted a handful of obvious windloaded features from strong valley winds near town. Wind drifted slabs were 2″ to 5″ thick, pencil hard. Some would crack after undercutting and stomping on the slope, others would crack as we crossed the slope, with shooting cracks up to 10′.  Slabs were all small and localized to easily identified features such as rollovers or in gullies.
The rest of the terrain that we traveled on was all bottomless facets with some wind texture on the surface.

 

Photos:

Toto, we’re not in Kansas anymore

CBAC 2020-21 Observations

Date of Observation: 01/15/2021
Name: Zach Guy, Zach Kinler, Jared Berman

 

Zone: Southeast Mountains
Location: West Brush Creek towards Coffee Pot Pass
Aspect: East, South, West
Elevation: 9,000 to 12,800′

 

Avalanches: We intentionally triggered a hard slab avalanche on a small, heavily windloaded terrain feature on an east aspect below treeline. The slab was about a foot thick and about 300 feet wide, D1.5 in size. It was made up of windrifted snow failing on weak facets.
Weather: Clear skies, mild temps, periods of moderate to strong gusts drifting faceted snow.
Snowpack: We traveled mostly on low angle terrain below treeline and some steeper slopes on westerly aspects near and above treeline. Below treeline, we triggered about a dozen collapses and shooting cracks on the 12/10 interface which is about 15″ down, 4-5mm depth hoar. Collapses were mostly in concave or leeward terrain features that had collected additional windloading from last night’s winds. Wind drifts were pencil hard, 2″ to 8″ thick on average, and localized to mostly just drainage bottom. The drifts themselves also cracked easily under our weight where they formed on near surface facets. As we gained elevation, it appeared that winds mostly just scoured snow away on all aspects. The few drifts that we found were thin and unreactive. On steeper westerly aspects, we didn’t observe any signs of instability; the snowpack is generally thin and all weak facets, apart from a wild mess of firm wind crusts and sastrugi on the surface.
We targeted a test pit just above the crown of a large avalanche that ran naturally in late December on an east aspect above treeline. The slab was 60 cm thick, and is faceting throughout, but still has about 10 cm of 1F- in the midpack. The failure layer was 2-3 mm facets either above or below a soft (4F) decaying meltfreeze crust. Stability tests on the structure today produced hard, non propagating results in an extended column test (ECTN28 x 2), and propagating results in a propagation saw test (PST40/100 END x 2 on 20201210) just above the crust.

 

Photos:

Wind Board Is The New Pow Bro

CBAC 2020-21 Observations

Date of Observation: 01/15/2021
Name: Evan Ross

Zone: Northwest Mountains
Location: Kebler to Scarps Ridge
Elevation: 9,000-12,000

Avalanches: Nothing new observed

Weather: Few clouds, with continued moderate to strong winds

Snowpack: Covered ground and moved around, just trying to get a better idea of conditions after the wind event. Mostly just traveling on roads and looking at the terrain. In the big picture, there was way more wind erosion on the snowpack, then any actual wind-loading. I really didn’t see much of any lens-shaped, pillowy, or well loaded looking terrain. I’m sure there was some form of loading, maybe NTL behind some tree fences or something. Though I wouldn’t say you could claim there is specific terrain with common characteristics holding fresh wind load, and instead, any fresh wind-loading looked more isolated to non-existent. Lots of wind-board and sastrugi out there unfortunately.

I also spent a brief period in lower Elk Creek. Some of the snow surfaces down low had some texture in the protected areas, but the snow surface was still soft and more capable of a facet sluff than a slab problem. The views I had up toward the start zones looked more like wind texture and not so much for lens-shaped loading.

CB Nordic Explorers

CBAC 2020-21 Observations

Date of Observation: 01/14/2021
Name: CB Nordic Explorers

Zone: Southeast Mountains
Location: Crested Butte

Avalanches: A skier in our after school Nordic programs remote triggered this little guy walking just off of the groomed trail. You can see his tracks approaching the slope on the bottom lookers right. Wow! No teenagers were harmed in the making of this observation.

Photos:

Upper Slate River

CBAC 2020-21 Observations

Date of Observation: 01/13/2021
Name: Zach Kinler Evan Ross
Zone: Northwest Mountains
Aspect: East, South East
Elevation: 9,600′-11,600′

Avalanches: No recent natural activity. Intentionally ski triggered 2 harmless D1 loose dry avalanches on a steep pitch near valley bottom where the snowpack was thin and mostly faceted.
Weather: Warm start to the day with temps near freezing, strong solar gain and calm wind. By early afternoon, high clouds drifted in and wind increased. Light to moderate NW winds blew on ridge top as well as open east aspects below tree line.
Snowpack: Many of the lower elevation slopes near valley bottom facing E and SE aspects are shallow and unsupportive to skis. There is much variability in depth and structure here with mostly weak over weak. Moving from lower elevations to 11K, the snowpack depths double with more of a supportive midpack over weak, faceted snow near the ground. This terrain is right in the heart of our stubborn Persistent Slab problem. We experienced no signs of instability or recent avalanches however we managed this problem by focusing on consequences, skiing short to medium-sized slopes up to but not greater than 35 degrees that were planer, had clean run outs and lacked obvious trigger points such as trees, rocks, and convexities.

 

The rotting continues

CBAC 2020-21 Observations

Date of Observation: 01/12/2021
Name: Zach Guy

 

Zone: Northwest Mountains
Location: Slate
Aspect: North East, East
Elevation: 9,000 to 11,400′

 

Avalanches: In a path that ran in mid-December, we skier triggered a long-running facet sluff that gouged to the ground. It ran about 1,000′ vertical feet and entrained about a foot of weak faceted snow, about D1.5 in size. Good communication from partners watching from ridgeline prevented this sluff from surprising the skier. It started off very small and slow but picked up quite a bit of speed and punch by the end.
Weather: Inverted temps, thin broken cloud cover in the afternoon, calm winds.
Snowpack: In the windsheltered terrain that we traveled in up to 11,000 feet, the slab has mostly faceted away. There is some residual 4F or 4F- faceted midpack. Test results on this structure were unreactive.
We tested a windloaded terrain feature near ridgetop (11,300 feet). The slab is noticeably denser (up to 1F midpack), and the test produced hard propagating results.
In some terrain that avalanched in mid-December, the snowpack is entirely fist hard, large grained facets. The structure is quite weak, and now capable of producing full-depth sluffs in steeper terrain.

Photos:

Purple Ridge obs

CBAC 2020-21 Observations

Date of Observation: 01/11/2021
Name: Eric Murrow & Zach Kinler

 

Zone: Northwest Mountains
Location: Purple Ridge standard up track area
Aspect: North East, East, South East
Elevation: 9,600′ – 11,600′

 

Avalanches: nothing new to report
Weather: clear skies, nasty cold at valley bottom along the slate gave way to pleasant conditions just a few hundred feet above valley bottom and above. Very light winds near ridgetop with no drifting snow observed.
Snowpack: Ascended generally easterly terrain to ridgetop. This is a snow favored area around Crested Butte with the deepest snow accumulations in the forecast area. No signs of instability noted like collapsing or cracking. Very little traffic in this area since the 12/29 storm. Near treeline probing revealed a snowpack around about 120cm or so deep with a very dense slab resting on top of the basal weak layer. See profile for a look at the snowpack in sheltered terrain in this area. The slab is dense, up to pencil hard BUT the weak layer remains uninspiring with minimal signs of improvement like rounding or increased hardness. Stability tests only confirmed the stubborn nature of human triggered avalanches, you would need to find a thinner spot in the slab to get a result, but if you did, sure would be an ugly avalanche.

Went to have a look at the large, natural avalanche from 12/29 on Purple Ridge to test adjacent slopes and identify how deeply it failed. Probing through part of the bed surface revealed that this avalanche failed very near the ground. Even with 20cm of refilled snow on the bed surface, the snowpack was generally only 30 to 50 cms deep in total. Tests adjacent to this slide produced an ECTP 16 on the same interface just 20 to 30cm above the ground. Probing hangfire showed 150 – 200cm right below ridgetop quickly tapering to 130cm-ish 30 to 50 feet below ridgetop. The slab in this drifted area was mostly pencil hard helping to insulate the weak layer from the weight of a person, but I was surprised at how poor the weak layer continues to look (4finger hard) and I still remain uninspired to test the waters on big, drifted terrain features. Definitely stubborn to trigger but not confidence-building assessments. Bed surface of this previous avalanche path consists of lower density, small-grained facets sitting on a slick, crusty bed surface….a recipe for certain avalanches once it is reloaded by a significant storm.

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