Snow Observations List

There were large slab avalanches that happened on both sides of the valley.  Northerly and southerly aspects.  

I was particularly impressed by the width of one of the slides Nate observed yesterday.  (one of the 2 photos attached).  That slide in the photo looked to be an average of about 2-4' deep (6' deep in places) and about 800-1000' wide, spanning across lots of different terrain features.

I also noticed that the main south facing slide path off of Miller Mountain avalanched very large as well. (the same avalanche path where the snowbiker was killed last winter)  I couldn't see the crown, but the debris ran to the valley bottom and appears to have flattened a large stand of mature timber.

VERY windy out there today.  Primarily SWerly, but blowing in all directions and moving LOTS of snow.  Natural avalanches likely happening today.

As seen from the highway, Lamar Valley, SE aspect. Mid-morning today. -3°. 

In Cooke City a large storm dropped 4.5" of snow water equivalent (4 feet of snow) and there were a few avalanches reported during and immediately after the storm. We saw one large avalanche on a south facing slope on Meridian, and a smaller wind-loaded slope that avalanched on Mt. Abundance (photo). We saw no other activity. Our concern is the interface between the old snow and new snow. The avalanche activity seemed to break here and on slopes with a wind-load it's worth being extra careful.

Meridian: R2, D2.5 (likely last night, 2/22)
Abundance: R3, D1.5 (maybe on 2/21)

We rode through Sunlight Basin, Sage Basin, and Cabin Creek today looking for avalanche activity from the most recent storm that dropped 15" of snow (1.5" of snow water equivalent) in the Taylor Fork area. We did not see any signs of recent avalanches. Today the wind blew from the NE, and it was drifting the new storm snow throughout Cabin Creek and Sage Basin. Since the wind is transporting the storm snow it is still possible to trigger an avalanche several days after the storm.

From an email:

Many collapses. HST 15cm. NSFing on the surface. Light winds out of the E, S.

Several small wind slab pockets in steep, wind loaded areas of terrain. This photo is the largest one that released. Bison, watch out!

On my drive back from the park, I noted a few others. Surprisingly, nothing on those S slopes around Meridian went.

-Old Man Rays, released mid slope, as well as a small pocket below the cliff in sympathy. SS-N-R2-D2-I(?)

-Miller Ridge, SW aspect at about 9500’, large crown. That’s all I could see.

Photos of some recent natural avalanches near Cooke City today attached.  All of the slides observed appeared to just involve new snow from the Feb. 20-21 storm.  (occuring on all aspects, but primarily on NE aspects)

New snow:  generally about 50-80cms of settled new snow from Feb. 20-21.

Quite a bit of collapsing experienced today while breaking trail, particularly in the lower elevations.  

Snowpit attached from a SE aspect at 8500'.  HS: 170.

ECTP15- 55cms down, at new/old interface.

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from 23 February email:

Residents of Silver-Gate caught a glimpse of a large natural avalanche south of Silver Gate on Wall Mountain. The size is uncertain, but it knocked down a stand of trees. Two people state that they believe they heard the avalanche in the pre-dawn hours. 

We skied along the ridge to the Ramp. At times we had good visibility and were able to glass the west side and saw no avalanche activity. Alex saw only small slides yesterday to the south of the ski area. A squall in the pre-dawn hours rapidly dropped 3" of 18% snow (.5" SWE).  Winds had died down and there was no current loading as we traversed, but by the time we exited at noon snow was falling and winds were blowing north and east as the cold front hit. We dug a pit about 4 feet deep and found the new snow was not breaking in stability tests. We were encouraged by the lack of avalanche activity and no significant cracking on wind-loads, but we were still nervous given that 4 feet of snow had just fallen. We were not confident in the stability, but that will change with time as the snowpack adjusts to the heavy burden of new snow.

From IG: “Ski cut trigger. West facing. 9800ft. Big sky area.”

This afternoon we went for a tour up Mt Ellis. The winds ripped across the ridge from the west, heavily loading the east to northeast aspects and building up some impressive cornices. We avoided the wind-loaded slopes and dug a pit in a protected meadow on a northeast aspect below the ridge. There was little evidence of wind loading and we observed strong stability in our pit. 

Our group toured around beehive, middle and bear basin. The wind has made the cornices huge at ridge lines and created obvious pillows and drifts and added texture to the snow surface and made the new snow noticeably denser than yesterday. The newest 15-20cm fell upside down. In our pit we noticed the top 20cm of new snow was F+ consisting of primarily large graupel, below that, the 20cm of new snow from yesterday was F- with snow trending from 4F to 1F over the next meter below. We had ECTN4 where this denser new snow from today overlayed yesterdays lower density snow. The NSF layer was about a meter from the surface and unreactive in our tests. Today was almost unskiably deep, and the nature of the new snow structure made burying a tip and pearling an expectation. 

Drove up to Bridger at noon and saw a large avalanche on along the road north of the fire station. It was 75’ wide, 1-1.5’ deep and 25’ vertical. HS-N-R4-D1.5/2. It was on an east facing slope, south of the long slope that has cornices. The slope with cornices hadn’t slid at this point. On the way home at 3:30 the larger slope with cornices had slid. It was very big, possibly R5. 1.5-2’ deep, 200’ wide, huge chunks of hard slab and cornice. Looks like new wind-loaded snow with some gouges into older snow.

From Olson creek I had a cloud free flat light view of the ridge from Saddle to Bridger Peak and looked with binoculars. There was a wind slab just north of quarter saddle that did not go over the cliffs. Probably 1-2’ deep, 30’ wide of new snow. There was a large wind slab on the north half of Between the Peaks (250’ wide) and one similar depth wind slab in the Pinnacles (100’ wide). Both of these broke 1-3’ deep immediately below the cornice and did not entrain much snow or propagate very wide or downslope given how much new snow there was. I could see the debris from the slide between the peaks which ran over 1000’ vertical to the top of the runout zone but relatively low volume.

Biggest of the cronies not pictured but around 3-5 m in height at the biggest on the west side of the ridge

From email, "At 12:45 p.m. I saw Climax run naturally. SS-N-R2-D2-I. The low visibility and distance made it hard to tell how deep the crown was, but based on there not being much volume of debris and it not running very far I’m guessing it was within the new snow/storm interface and didn’t step down to any buried PWL."

We rode through first and second Yellowmule at Buck Ridge. There was a natural avalanche below the cornice line on the headwall above second Yellowmule that broke within the last 12 hours as it was not covered by any new snow. From a distance, it looked to be ~200' wide and broke 1-3' deep. I believe it failed just under the storm snow, not of deeper weak layers, but a very large cornice, hang fire (snow that didn't avalanche above the crown), and ongoing loading from snow and wind made it unsafe to investigate more closely.

The storm total farther back in the area was 20" of thick snow. Strong winds were creating heavy drifts in many areas. Human-triggered avalanches are likely on steep slopes, especially those loaded by fresh drifts. We dug one pit near the entrance of 2nd Yellowmule, we saw the buried weak layers, but they did not react in our stability test... We tested the snowpack for scientific interest. We planned to, and did, stay off steep slopes and the runout zones of slide paths and recommend that folks do the same until the storm is over and the snow has a chance to stabilize. The lack of propagation is a good sign for longer term stability, and I expect slopes to stabilize relatively quickly once the storm is over and wind-loading lets up. 

Today I toured up to Chestnut Ridge via Goose Creek Trail. I noticed many wind deposits on the upper ridgeline that were actively thickening from the gusty Western winds (roughly 25mph average at the ridge). I dug a quick pit at 7370' on an Eastern aspect under the ridgeline and got some very touchy results. My HS was 125cm. I got a CT4, sudden collapse, Q1, breaking within a thick layer of advanced basal facets. The slab that came off was 85cm in height and very cohesive. Between the obvious wind loading near the ridge and my test result (which, I'm sure I could have replicated based on my probing of the area), our party decided to stay completely out of avalanche terrain and ski a few runs on mellow meadows and glades nearby. Minimal new snow fell during our tour -- just broken skies and a healthy dose of wind moving through the area. Stay safe out there through this storm cycle!

We snowmobiled and skied near the Throne and stayed on slopes less than 30 degrees and out from below any slopes steeper than 30 degrees. At 11:00am at 7,500' we measured 14" of new snow equal to 1.2" of snow water equivalent. It was snowing one inch an hour and wind was moderate with strong gusts. Avalanches of new snow were likely on steep slopes and very likely on steep wind-loaded slopes. Conditions will get more dangerous as more new snow is expected over the next couple days. We dug a pit at 7,500' on a northeast aspect. HS was 157cm and we did not see any reactive or concerning weak layers, but the new snow and wind-drifts are enough to create large, dangerous avalanches.

Our party toured up to Prayer Flags this morning. We found 10-15 cm of low density new snow drifted much deeper in some places. Their were moderate winds out of the west to north. We stomped small soft slabs of wind drifted snow at the ridge breaking 10-15 cm deep and only 5-10 feet wide at the new/old interface. We also witnessed small point releases on very steep slopes and around cliffs triggered by spin drifts. We Found cracking in the new snow on both East and West sides of the ridge between Beehive and Middle. On unprotected solar aspects you could feel a sun crust under the new snow. Places unaffected by the sun were bottomless feeling. We had no note worthy results in our quick test pit.

Dug a quick pit on a west aspect on the west side of Woody Ridge. HS was 178 cm. ECTN 29, 1.5’ below surface on 1.0 mm rounding facets. Skied off the west side of the ridge. The snow was more wind drifted towards the bottom of our run, 4-6” wind skin in spots. We didn’t see any signs of avalanche activity. Snow started falling lightly around 1400.

On Saturday (2/18) we toured into Maid of the Mist and dug a pit on a northern aspect at the base of the skinny maid. Our results indicated that where there was wind loading, it was very likely to fail and propagate. In addition to the ECTP 1 on the wind slab, we noticed shooting cracks on isolated pockets of wind loading.