Propagating results

CBAC March 26, 20212020-21 Observations

Date of Observation: 03/26/2021
Name: Zach Guy and Jack Caprio

Zone: Southeast Mountains
Location: Mt. Emmons
Aspect: North East, East
Elevation: 9,000 to 11,500′

Avalanches: One small wind slab likely ran naturally yesterday in Coon Basin (SE aspect, ATL).
Skier triggered a handful of shallow sluffs on steep, northerly terrain, about 6″ deep or less.
Weather: Afternoon tour brought overcast to broken skies. Brief convective pulses of moderate snowfall (S2) with an inch or so of accumulation, generally light winds with a few stronger gusts associated with the snow squalls.
Snowpack: Looking for feedback for persistent slabs in the type of terrain we’ve been warning about: shallow/previously avalanched, previously windloaded. Slabs are getting a little thicker now and we didn’t feel comfortable ski cutting or really getting onto suspect slopes to get a feel for how reactive they are. A few strategically placed pits along flanks or smaller terrain features produced a mix of propagating and non-propagating results on fist hard facet layers (1.5-2.0mm) on old bedsurfaces, generally 45 to 65 cm deep. The most concerning structures and a propagating result were on slopes where previous wind drifting created denser, harder layers above these buried facets, making for a more dramatic hardness change at the weak interface. Wind sheltered terrain held a softer slab and a less-distinct transition to these facets, with non-propagating results. Previous wind drifting and scarier structures were not apparent on the surface, but evident with probing or an understanding of local wind patterns. We avoided those types of slopes.

Photos:

: Small wind slab that likely ran yesterday. Small sluffs next to the crown today.

: Most concerning structure was on an east aspect with crossloading from previous northerly winds.

: A more windsheltered slope, less reactive

: Another relatively wind protected slope.

Mt Emmons

CBAC March 26, 20212020-21 Observations

Date of Observation: 03/26/2021
Name: Evan Ross

Zone: Southeast Mountains
Aspect: East, South East, South
Elevation: 9,300-12,300

Weather: Calm to light winds with a few stronger gusts transporting snow. Mostly cloudy sky with convective cells moving through and creating quick bursts of snowfall. Maybe an inch or two of new snow accumulation today, but it was settling quickly.

Snowpack: Potential wind slabs were small and from what I observed were really confined to right near the ridgeline or cross-loaded terrain features. Otherwise, the cream was getting thicker with periods of sun between the clouds. Similar to yesterday’s ob in Washington Gulch, there was about 4″ of recent snow accumulation down low and around 8 to 10″ up higher. No avalanche problems were observed outside of the potential wind-loaded terrain features. One snowpit at 11,300ft on a 33 degree south facing slope had about 8″ of new snow on top of a very stout crust with a matrix of other stout crusts and percolation columns below.

: East 11,900ft. Good bit of effort to start pushing a piece of the thicker drift down hill as a small thick sluff

Weekly Snowpack, Weather, and Avalanche Summary 3/26/21

CBAC March 26, 20212020-21 Observations, 2020-21 Weekly Snowpack Summary

Date: 03/26/2021

Name: Jack Caprio

Zone: Crested Butte Backcountry

Consistent moisture throughout the week rewarded us with many pow days in the snow-favored areas of the zone. Check out the weekly summary to see how these storms impacted avalanche conditions.

Anthracite Mesa-Coneys

CB Avalanche Center March 26, 20212020-21 Observations

Date of Observation: 03/27/2021
Name: Andrew Breibart

Zone: Southeast Mountains
Location: Washington Gulch-Coneys
Aspect: North East, East
Elevation: BTL

Avalanches: NA-poor visibility
Weather: Obscured skies with S1 and S2 snowfall. Calm. On the skin out, obstructed skies, calm and intermittent S-1 snowfall.
Snowpack: Supportive snowpack valley bottom to the ridge. 48-hour snow: 3 to 6 inches with 8 inches on the leeward side of the ridge line. New snow seems to be bonding to the last melt freeze crust. Triggered shallow storm sluff at the convex entrance to first bowl.

Gothic 7am Weather Update

CBAC March 26, 20212020-21 Observations

Date of Observation: 03/26/2021
Name: billy barr

Zone: Southeast Mountains

Weather: Very light, scattered dense snow Thursday, then light snow after midnight so the 24 hour total is 4″ new and 0.24″ of water. Snowpack is at 49½”, the deepest since mid February. Calm yesterday and so far today. High yesterday 33F, low today 18, current 19. Overcast with a very light snow.

Cream surfing good

CBAC March 25, 20212020-21 Observations

Date of Observation: 03/25/2021
Name: Evan Ross

Zone: Southeast Mountains
Location: Coneys
Aspect: North East, East
Elevation: 9,000-11,000

Weather: Mostly Cloudy. Several nice burst of snow interspersed with sun and greenhouse conditions. Calm winds.

Snowpack: About 4″ of new snow down in the valley and about 8″ near the top of Coneys. New snow was well bonded to the supportable crust below. Hand pits wouldn’t pop anything above the crust and no signs to instability. Same results at ridgeline. Old tracks form yesterday were still visible off the highest point of Coneys. The new snow was definitely feeling the heat, but man the cream sure is surfing good.

: Dragging a hand through the middle of small columns without results.

Snodgrass Profiles

CB Avalanche Center March 24, 20212020-21 Observations

Date of Observation: 03/24/2021
Name: Ian Havlick

Zone: Southeast Mountains
Location: Snodgrass Frontside
Aspect: North, North East, East
Elevation: 10,200-11,500

Avalanches: none
Weather: BKN moved to OVC with S-1 snow showers late afternoon. no accumulation. temperartures 20-28F. Mostly calm.
Snowpack: I dug 12 full profiles today for a CU researcher BTL snodgrass, N-E aspects. No stability tests as I was collecting density data in treed terrain, but still same poor structure, P-hard slab above 20-40cm 2-4mm F+ DH. has improved a bit from same locations dug 1 month ago, F- DH then, compared to F+ DH now, but still weak, and stiffer slab. General HS in areas dug between 11, 200 and 10,000 was 90-130cm.

Washington Gulch obs

CBAC March 24, 20212020-21 Observations

Date of Observation: 03/24/2021
Name: Eric Murrow

Zone: Northwest Mountains
Location: Washington Gulch – obs from near TH to treeline on Baldy
Aspect: North, North East, East, South East, South, South West, West, North West
Elevation: 9,400 – 11,900′

Avalanches: Good views midday showed no recent avalanche activity.
Weather: Partly cloudy skies, with a good amount of sunshine in this area. Snow showers developed in areas east and west of Elkton, but no snowfall from 1130 – 430. Some thunder was heard from nearby convective cells. Maybe an inch or so of new overnight in this area. Winds were variable and light – very little blowing snow observed at upper elevations.
Snowpack: Covered a lot of ground on the snowmachine looking at sunny slopes. Most sunny terrain SE-S-SW had moist to wet surface snow sitting on older, well-developed melt/freeze crusts. On these sunny slopes, I anticipate the incoming storm system to fall on supportive crusts without much concern for developing a Persistent Slab problem. Shoulder aspects, east and west, had a few inches of dry snow resting on soft/melf freeze crust with additional soft crusts in the upper snowpack.

Shaded slopes facing very close to due north remain dry without crusts present, but as soon as you tilt eastward crusts show up below the snowfall since Saturday night. There are two layers of interest in the upper snowpack on shaded slopes, the upper being a melt/freeze crust with 1mm facets below and the other the mid-march weak layer with 1-1.5mm facets. At one near treeline site facing northeast, HS 155, I got moderate propagating results on the mid-march weak layer. Test results grabbed my attention – triggered avalanches are possible in the upper snowpack with a similar structure.

Closer to Washington Gulch TH I checkout a north slope with a much shallower snowpack, closer to 90cm, and found a fairly weak snowpack. Just an inch or two of recent snow sits on a soft melt/freeze crust with very weak 1-2mm facets below. A poor-looking structure for future loading events.

Photos:

: Test profile from northeast slope near treeline

: Shovel Tilt Test produced clean sheer below a crust in upper snowpack under moderate taps.

Small persistent slab

CB Avalanche Center March 24, 20212020-21 Observations

Date of Observation: 03/24/2021
Name: Jack Caprio
Zone: Southeast Mountains
Location: Lower Slate
Aspect: North, North East
Elevation: 9k-11k

Avalanches: Intentionally ski triggered a small persistent slab avalanche on a wind-loaded feature just off a road cut. The avalanche broke in two places: On the most recent interface about 10-15 cms down from the surface, and on the 3/10 interface which was buried about 40 cms.

Weather: Overcast and warm.

Snowpack: I stayed below treeline all day near the border of the NW and SE zones. In the protected areas where no wind loading has occurred the snowpack is very weak top to bottom. Generally, no slab avalanche concerns on protected northerly slopes due to lack of a slab in this area. As I stepped out into open skied, wind-affected areas slabs became more common. Slabs were generally soft but did reach 1F hardness just above the 3/10 interface on the slide I triggered. The 3/10 interface consists of 1-1.5 mm facets on due north slopes in this area.

Photos: