Date: 02/12/2021
Author: Jared Berman
Zone: Crested Butte Backcountry
AVALANCHES, AVALANCHES, AVALANCHES! Our snowpack is getting deep and avalanches are becoming large! This week our zone has seen the most impressive avalanche cycle of the season. Check out the weekly snowpack summary to learn all about it.
Date of Observation: 02/12/2021
Name: Zach Kinler
Zone: Northwest Mountains
Location: Anthracites
Aspect: North, North East
Elevation: 10,000′-11,400′
Avalanches: No new avalanches observed, no vis of the surrounding terrain.
Weather: Cloudy, dumping snow for most of the tour, S5 average. Winds were calm to light in sheltered terrain increasing early afternoon with moderate gusts near tree line. Temps felt perfect for making snow.
Snowpack: 5″ on the skin track in the morning around 10:00 and 6″ when we returned at 14:30. 11″ HST and still going!. Small sluffs on the first couple runs turned into more storm slab type instabilities(upper 6″ of new snow) by the last run as increasing winds and snow density gave some “slabby-ness” to the newest snow. Managed the deeper weak layers by avoiding drifted slopes and the larger, un-supportive slopes and convexities.
Date of Observation: 02/12/2021
Name: Evan Ross
Zone: Southeast Mountains
Location: Evans Basion, Mt Emmons
Aspect: East, Southeast, South, Southwest
Elevation: 9,300-12,300
Avalanches: A few small sluffs out of steep terrain, otherwise mostly poor visibility.
Weather: Near and above treeline were just nasty of course. Lots of snow transport and westerly winds strong enough to make you stumble. Measured about 7″ of new snow early afternoon at 10,500ft.
Snowpack: Other than small test slopes, I didn’t travel in avalanche terrain. Traveled through all the elevation bands, but didn’t spend much time up high due to the wind and weather of course. Below treeline, I got on a number of steep test slopes without results. I think the new snow in those areas wasn’t doing much for a storm slab avalanche problem, and the persistent weak layers were simply too deep in the snowpack, resulting in supported slopes that couldn’t displace if there was a collapse. Got close to other bigger steep slopes, also without anything notable. Many of those bigger slopes had also previously avalanched with crown lines still visible.
Date of Observation: 02/12/2021
Name: Irwin Guides
Zone: Northwest Mountains
Location: Irwin Tenure
Avalanches: Near and ATL new Storm/Wind Slab trended Reactive to Touchy with increasing fracture length through the day, approaching D2 by the late PM.
Weather: HST: 8″/.65″ with mod/heavy transporting SW-WSW wind.
Snowpack: New snow is a bit upside down with 5″ of 10% on top of 3″ of 5%.
Date of Observation: 02/12/2021
Name: Zach Guy
Zone: Southeast Mountains
Location: Upper Cement
Aspect: East, South East
Elevation: BTL :9700 – 10900′
Avalanches: From 75 feet away, we remotely triggered a persistent slab that failed on depth hoar near the ground, about 2.5′ thick. The avalanche was small in size (D1) because it was on a small terrain feature. See photo.
Weather: Calm winds where we traveled, audible evidence of stronger winds aloft. Very light snowfall with a few, shortlived moderate pulses. About 2″ storm total.
Snowpack: Traveled to the shallowest part of our forecast area and found the depth hoar layer about 50 to 80 cm down, (12/10 layer) is very sensitive to human triggering. We experienced large, rumbling collapses and shooting cracks on almost every slope we crossed (SE and E aspects). Shooting cracks would span entire slopes and through mature aspens. Collapses would visibly shake trees several hundred feet away. Say no more, snowpack, we’ll stick to low angle terrain.
In Lower Cement Creek (down valley from Deadman’s Trailhead), snow depths are still quite shallow and there doesn’t appear to be enough volume in the start zones or tracks for natural activity to hit the road yet in most terrain
Photos:
Date of Observation: 02/12/2021
Name: billy barr
Zone: Southeast Mountains
Location: Gothic Mountain
Weather: There was no snow from sunrise yesterday until around 4 a.m. this morning when it started moderately. New snow so far of 3½” nd water content 0.24″ as the snowpack reaches 45″. Currently obscured cloud cover with moderate snow and no wind. Mild weather holds with the high 33F, low 18F and current 21F. I did hear a slide run off of Gothic but that straight face runs regularly and is not really much of an indicator. Unless you are right under it. Which I discourage. Therefore there is a high hazard for fools.
Date of Observation: 02/11/2021
Name: Alex Tiberio
Zone: Southeast Mountains
Location: Gothic Mountain
Aspect: South East
Elevation: ATL
Avalanches: Natural Avalanche around 2/11. (CBAC Note: Best estimate from these photos is that a wind-loaded slab released near ridgelines and further stepped down into a persistent slab avalanche below the cliffs. This avalanche appears to be large to very large in size.)
Photos:
Date of Observation: 02/11/2021
Name: Zach Kinler
Zone: Northwest Mountains
Location: Anthracites
Aspect: North, North East, East
Elevation: 10,000′-11,400′
Avalanches: One small Wind Slab in Red Lady Bowl, east aspect off the lookers left ridge.
Weather: Mostly cloudy, cool west breeze at ridgetop. Minimal snow transport near tree line but winds were moving snow in alpine terrain along the Ruby Range and Scarps Ridge.
Snowpack: Nice to have to use a probe to find the bottom of the snowpack instead of a ski pole or my hand! The 2/3 interface was 70 cm deep and easy to identify by the graupel layer however stability tests revealed small facets a few centimeters below the graupel. There were 2 Surface Hoar layers around the 1/19 interface with a few centimeters of 1F snow in between. This “sandwich” was failing as one in tests. This interface was buried 110 cm deep. Both interfaces popped in short column tests but produced no propagating results in ECTs. We observed no cracking or collapsing. Warm temps and a deeper snowpack have allowed these weak layers to adjust, for now. They will be tested this weekend with another strong storm moving in.
Photos:
Date of Observation: 02/11/2021
Zone: Northwest Mountains
Aspect: North East
Avalanches: That old crown in runaway was 4+ easily. That thing was seriously impressive and a huge eye opener. (CBAC Note: That avalanche ran in the evening of the 5th or morning of the 6th, and made it from the top of Schuylkill Ridge to valley bottom.)
Snowpack: Lots of new snow on schuylkill. 12-15” easily. Breaking new trail entire way up didn’t feel any signs of instability but super efficient wind loading all day led to sluffs I believe
Date of Observation: 02/11/2021
Name: Evan Ross Jack Caprio
Zone: Northwest Mountains
Aspect: North East, South East
Elevation: 9,000-11,000
Weather: The NE Mountains cloud cover was mostly cloudy, becoming partly cloudy and back to over cast by the afternoon. Ooo fun. Plenty of sun out there to warm and thicken the snow surfaces on sunny slopes. We didn’t have much wind exposure. However those winds were obviously cranking in the alpine and even moving snow down in the open valleys at times.
Snowpack: Basically, we ended the day with another BTL tour on NE that continued to highlight the decreased sensitivity of the persistent slab avalanche problem below treeline. Despite what the weak layer is, those weak layers are hiding below a growing and strengthening slab. We only observed one collapse. That was after like 12 He-Man jumps on a small slope connected to a bigger slope, 10,500ft at ridgeline, NE. That collapse shot cracks through the connected slope for a good 100ft or so. Otherwise, we traveled on other steep slopes with no red flags and chose terrain features with lower consequence. For these NE slopes, the HS averaged in the 120 to 140cm range. Heading into the next storm, it will be the same December and January persistent weak layers of concern.
We spent a little time on some mid 30 degree SE facing slopes around 10,500ft. The early February crust was now down about 45cm’s. That crust and any facets below the crust were not particularly notable at this location. Unfortunately, we didn’t get to spend more detailed time looking at that interface. It didn’t give us any feedback toward obvious signs of instability. The early January interface still felt like the layer of concern and that interface was laying in the lower 1/3 of the snowpack.
