Snow Observations List

Observed a large wet loose (D1) in Zimmer Creek today off SE facing cliffs. Likely happened 1/29. There were also other smaller wet loose avalanches nearby on south facing cliffs 

Today, we toured south of Cooke City, up Republic Creek and Republic Mountain. We spotted widespread, weakening snow surfaces: surface hoar feathers at lower elevations, faceted snow on cold, shady slopes up high, and faceted snow beneath crusts on solar aspects. Our pit on an E aspect at 9460' did not produce unstable test results, but showed the top 1.5' of snow to have faceted and weakened during this bout of high pressure. These layers are not concerning now, but will certainly be top of mind when the next storm system arrives over the weekend. 

We spotted several loose wet avalanches that occurred yesterday in steep, rocky terrain up Sheep Creek. We also noted an old, deep persistent slab avalanche on a NW' aspect near the south end of the Republic Creek drainage. This likely broke around a week ago. 

Skies were clear, winds were calm, and temperatures were warm in the sun and chilly everywhere else. 

We skied up west Woody Ridge and skied down into Hayden Creek about 500 feet, then back up and over, and out Republic Creek.

Skies were clear with calm winds and a light breeze at the ridgetop. Temperatures were still mostly cold, single digits down low and teens up high in the morning. The sun felt hot mid-day, snow bombs were falling off trees and there were some small rollerballs around steep rocks on southerly facing slopes.

We saw one old, but very large persistent slab avalanche further up Republic Creek (pictured). It was on similar aspect and elevation as a somewhat more recent persistent slab in nearby Hayden Creek, North-northeast, 10,000'. It appeared to be 6'+ deep and 500'+ wide. The bed surface and crown had been partially drifted in, so it seemed it was probably at least a week old...?

There was also a recent cornice fall on a very big steep slope up Republic Creek (picture) which did not trigger anything large or deeper, but entrained some snow and ran over a thousand feet vertical.

We dug a pit at 9,900' on a west aspect. Snow depth was 150cm (5 feet). We had an ECTN11 below 3 inches of snow on top of small sugary facets near the surface. There were soft (4f+) sugary facets at the bottom of the snowpack, but they did not break in an ECT or with extra force. Snow depth above 9,000' was ~4 feet average based on a few places we probed as we toured up.

There were signs of a lot of previous wind up high. It has been a few days without wind, but there are probably some isolated instabilities of small stiff wind slabs sitting on facets which could be triggered.

We saw most terrain in the motorized area north of Cooke City. We went passed Round Lake to Goose Lake wilderness boundary, around the north of Sheep Mtn. and Scotch Bonnet to Lulu Pass, out to Mt. Abundance, back south over Daisy Pass, and around town hill/Miller Rd., then up and down Sheep Creek to the top.

Skies were clear and wind was calm to non-existent with cold temperatures (singles to teens F).

We saw a handful (4-6?) of old wind slab avalanches of various ages. The most recent and largest appearing, but still not very fresh, was on the north side of Scotch Bonnet (attached photo). Most were D1-D1.5, the slide pictured was D2. 

We dug on the southeast shoulder of Mt. Abundance (profile attached). Snow depth was 3.5-4 feet and we had ECTNs. There were some soft-ish facets near the bottom of the snowpack. We also dug a pit in Sheep Creek and had an ECTX, snow depth of 4-5 feet. We did a lot of hand pits to look for recently buried facets. Small sugary facets were generally easy to find, buried 3-6" deep below soft snow. If and where snow is drifted into thicker slabs, these facets might make those slabs more reactive.

A lack of recent avalanches combined with minimal recent loading from new snow and wind point to avalanches being unlikely. The recent large persistent slab in Hayden Creek shows that although slides are unlikely they could be big. We would rule-out big slopes that are heavily wind-loaded, and otherwise feel ok in steep terrain while sticking to safe travel protocols (carry a transceiver, probe AND shovel, and only expose one person at a time to avalanche terrain).

While touring today, we saw a deep slab avalanche at the southern end of the Hayden Creek drainage. NE aspect. It seemed to be recent, likely in the last day or so.

Here are our observations from Cooke City today. Our plan was to tour up the south side of Miller Mountain as far as we felt comfortable. Winds were mostly calm during the day, and temperatures were darn-right cold all day, even on southerly aspects. It was -26F when we pulled into town.

The sheep creek drainage had a lot of evidence of prior wind transport, most non-sheltered aspects had textured snow. We dug a pit at 9600’, HS was 190cm! At 150cm above the ground, we encountered a 1cm thick melt-freeze crust with small facets forming over it’s surface. We also noted 4-finger basal facets all the way at the ground.

Our ECT produced nothing terribly remarkable. ECTN25 and ECTN26 on the melt-freeze crust. It could be a layer to look out for in the near-future. The snow above treeline began to stiffen, so we ripped skins around 10k feet and had a lovely ski down.
 

Toured into Pebble Cr drainage. 

2 to 4" of new, low density snow. 

Saw evidence of wind loading and two older, small slides on N facing aspects of some W - E sub ridge lines. Slides both appeared to be from wind loaded snow that broke right below the ridge line on the leeward side. 100 to 150' wide, 18" deep and running for 100 to 200'.

No cracking or collapsing found on any aspect during the tour and we couldn't get anything to move.

Nice snow wherever you could find a wind protected area. 

Isolated shooting cracks and windslabs above treeline south of Cooke City today. Strong winds from the west. Lots of wind transport going on up high. The vis was good this morning and I could see far for the first time in a while. I saw no new avalanches. 

Wind slab avalanche on E Henderson North of the large slide path close to Fisher Pk. R1 D2,1-2' deep, 200' wide. It broke aprx 200' below the summit mid slope. Phone was too cold to take photos. It looks like it broke on the 19th. Wind slabs 5-10" deep were easy to trigger on test slopes North o Lulu pass. Active loading today on upper elevation SW-SE aspects.  Multiple ECTX test results on S aspects at 8600' over the weekend. 

Observed freshly formed surface hoar near the top of Woody Ridge, 9800-10000 ft, W facing. Winds were light out of the N

Spotted another natural avalanche today on Woody Ridge north of the "KNBs." Northwest facing slope, crown elevation approx 9600'. Ran 1000 to 1200'. Unsure of when it went, we did not notice it this morning only this afternoon on the hike out. 

On 1/12 observed a D .5 soft slab near Long Lake above the snowmobile trail. Also saw some small dry loose activity on E facing terrain in Zimmer Creek. 

Observed a large avalanche on a west facing slope approx 10000ft, with a higher crown at 10200'. Crown depth 4-6'. HS-Ns-D2-R2-O . Ran 1000ft and into terrain I had previously considered safe.

A few dry loose avalanches on Climax, plus two small crowns. One was older and drifted in. The other was a small, recent wind slab.

Overnight it snowed 8 inches of low density at the yurt, and an additional 3 inches today. 
No avalanches or cr, co observed. Wind loading observed multiple aspects NTL. 

The main story from today was increased wind this morning and intermittently throughout the day. The moderate winds were actively blowing snow out of trees and over ridgelines, drifting snow into thick deposits, and there was evidence that wind had been active at high elevations (>9500'?) the last couple days. Today, winds strong enough to move snow started to reach all elevations. On Henderson bench we noted many thick, dense drifts while riding, and could see the snow surface textured from the wind up higher.

We looked at two 4-6' deep persistent slab avalanches that were reported yesterday on the east side of Henderson Mtn., which likely happened yesterday. Wind-loading was the likely trigger. There were not tracks near the larger one above the bench, where riders could easily get to, but they could have been filled in. The other slide was below the highest point below a cornice and likely natural. Both looked like they broke on facets at the bottom of the snowpack.

We dug a pit on Henderson Bench on a northeast facing slope, and one on Scotch Bonnet on a south facing slope (profiles attached). Both showed a 4' thick strong slab on weaker, faceted snow at the base. The weak layers are not terribly weak and didn't produce concerning test scores, so they may get better when they get a break from snowfall and wind-loading, but for now recent avalanches show these layers are weak enough and will produce more big avalanches as snowfall and wind continue.

Recent avalanches are clear evidence that the weak layers 1-2 feet above the ground are close to their breaking point. Continued snow and wind this weekend will make more of these big avalanches likely. Fresh drifts are also large due to all the recent snow that is being easily transported into slabs, and pose a significant hazard on their own.

Went snowmobiling north of Cooke City today near Round Lake. I saw about 20cm of new snow. I also saw some avalanches. There were a couple on E Henderson, one that I think happened today, a few on E Sheep Mountain, some shallower avalanches, and plenty of loose dry snow moving around in the steeps. Here are some photos. Some looked like they were from today, some are older. Lots of evidence of wind from the past day or so. 

Ian and I rode north of Cooke City, had good visibility, and saw terrain from Daisy Pass to Mt. Abundance back to Lulu Pass, around the south side of Scotch Bonnet, then back around the north side of Sheep Mtn. to Round Lake.

We saw many avalanches of various types and ages. Some occurred today and within the last 24 hours and some were up to a week old. Avalanche types ranged from 3-6' deep and broke on weak layers near the bottom of the snowpack to shallow soft, fresh wind slabs, and we saw one 3-4' deep slide that looked like it broke within recent new and wind-drifted snow (photo attached, north end of Henderson). 

The most notable avalanches were 2-3 slides that happened today:

1) When we rode away from our snowpit on Mt. Abundance we saw a fresh 3'deep x 10' wide slide that we might have remote triggered from the flat ridge above (photo attached). 2) About 45 minutes later, from a couple miles away, we saw a 4-6' deep avalanche that happened since we had been there, about 1000' up the ridge from our snowpit (photo). This slide was either natural or remote triggered by riders about 1000' away who were there after we were. 3) An avalanche on the south end of Henderson Bench that looked fresh and someone else thought happened today. This one was 6' deep and broke at the bottom of the snowpack.

There was also a very large avalanche on the north side of Fisher Mtn. that happened at some time in the last week (could have been 48 hours to a week old), regardless of timing, this slide further shows the deeper weak layers are a real problem as snowfall continues to adds weight to the snowpack.

Our snowpit produced an ECTX and had 4' of snow above a layer of surface hoar buried one foot off the ground with facets below.

Toured up the Boundary of Yellowstone Park today. Performed stability tests on two different aspects at two different elevations and these were our results.

1. 9100', South aspect, 120HS, Rounded FC at base. Recent storm interface found small .5mm FC 40cm down but no test results on that layer. ECTX
2. 9800', West aspect, Hs190cm, ECTX, LOC 110cm down, old MFcr/Facet Layer

No recent avalanche activity seen. One large collapse near a ridge line with thin snowpack (<70cm) 

Deep Slab on Northern aspects still a player. Rounding Basal Facets found on South and West aspects