Snow Observations List

From email 2/25/23: "... a good sized slab avalanche on Fan, NE Face. Crown height hard to estimate but looked like a 2’ or so. Maybe running on interface from when it got cold earlier in the week? Possibly deeper than that but sure could have loaded that much this week. Anyway- very white bed surface, good propagation, 200’ -300’ crown length, debris stopped on upper bench. D2.5. Likely triggered by cornice fall."

This natural avalanche was seen today on E. Henderson Bench.

On Saturday we toured up Sheep Creek and dug a pit on an SW aspect of Miller Mountain. We observed that the wind slab easily failed and propagated at this location. Shifting winds continued to load multiple aspects throughout the day. On the southwest ridge of Mineral Mountain we observed a large slide, approximately 200ft wide, that appeared to trigger another slide lower down on the slope. 

As we were skinning up a north facing slope on Knowles Peak, a roughly 20 by 20 foot section of the slope collapsed beneath our feet. We were on a slope steep enough to slide and it didn't, but we took that as a clear sign of instability and skied down. We then went up the south side of Arrow, mostly on mellower terrain before gaining the east ridge, and continued up. 400 feet from the summit we encountered a very steep, wind affected pitch, and decided not to continue up. We skied down the south gully, mostly in the trees and avoiding wide open slopes. South and east facing aspects were certainly heating up throughout the day and the ski down was hot pow. 

A snowmobiler saw this natural avalanche hit the Daisy Pass road within 10 minutes of riding by. He did a beacon search on the debris to confirm no one had been caught. It occurred about noon. This path is not very visible from the bottom and is not one that runs regularly. It killed a rider who was on the road in February 2012. The accident report has good photos of the path from afar.

Wind-loading in the start zone was the likely trigger since skiers and sledders do not access it.

From an email: "The crown was hard to see, but only looked a few feet deep where I could see it, but the debris pile was 10'+ on the road."

A big thanks to Dan Wykoff and Ben Zavora for providing the story and pictures.

We rode to Round Lake, Goose Lake wilderness boundary and Lulu Pass. We saw a coulpe of small and very steep avalanches that released in the new snow. We dug 3 pits and got ECTX or ECTN28 on the new/old snow interface 2-3 feet under the surface. We were glad to not find propogation. Wind ramped up during the morning creating white-out conditions at time. At Lulu Pass we went to investigate wind slabs and got a collapse (whumf) when we stepped on it. Wind-loaded slopes are dangerous right now. Slopes ae actively loading and sensitive to triggering.

Came across this very large cornice that appeared to have broken naturally sometime in the past 24 hours. Saw a few others that had broken recently throughout our tour, but none as large as this.

From IG message 2/24/23: HS-N-R2.5-D2-O. In emigrant gulch on an east aspect around 9k feet. Seemed to have stepped down on to a PWL, however it’s pretty tough to tell.

From IG: Skiers near Mt. Blackmore on 2/24 saw a large avalanche on the east side of Mt. Blackmore that appeared to have happened in the last 24 hours.

Triggered a small 2’ deep wind slab in new snow this afternoon.  NNE aspect 9,500’, approximately 38° slope.  Riding was excellent on all high North facing slopes and this was the only sign of instability we saw all day.  Wind was howling on the way out, lots of snow coming out of the trees and transporting at ridge tops.

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.”