Snow Observations List

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.

Wind slabs were the issue today. A lot had changed since Thursday when it was all sunshine and deep powder. Winds picked up and changed the landscape.

We found two small wind slabs that had released on their own, then watched a big one release froM a falling cornice, then triggered a small one (expected). 

Overall, winds were the perfect speeds for moving snow which they did all day. Looking south, there was a massive plume coming off Mt Bole.

Side note - temps in the trees were mostly hovering just above freezing. Lots of tree bombs dropping. The snow surface was a little damp by afternoon. Up high, the powder was still great where winds hadn't touched it. 

Avalanche Activity

We spotted 6-7 storm slabs that failed about 8-10 inches deep. There were 3 on the East face Blackmore, 1 on the north face, 1 on north facing flank, and 1 notable one in a steep below treeline cirque ENE facing (this one broke ~400 ft wide). A possible 7th was down the Fox creek drainage. It seemed a bit random where they happened and didn't. They likely occurred sometime late yesterday afternoon during snowfall and high winds. This instability should be mostly stabilized by tomorrow.

We didn't see any avalanches that broke deeper in the snowpack

Other signs of instability 

no collapsing or cracking

Skiing/riding quality 

5 star deep powder and hard trailbreaking, aka trenchtown

Snowpack

We had limited time and only dug one snowpit (attached profile image). We'd like to go back and poke around in some shallow rocky areas. Pit attached. General impression is that it is very deep, and mostly strong. The Shower Falls SNOTEL is at 124% of median swe.

Early December facets have gained a lot of strength, and stability is moving in the right direction. With so much new snow (and more coming Friday/Saturday), I worry about finding a trigger point in a thinner area and then causing an avalanche to break widely into deeper areas. After the Fri/Sat storm if no more snow or wind come for a little bit of time, stability should improve very quickly

Note

The photo of snow on the sign post really shows how snowfall has been steady, slow, and non-stop. My hunch is that initially snow piled up on top of the post. Then it began to sag (or creep) to one side but slowly enough to not break. With each storm a little more snow was added and the pile of snow crept more to the side. Cool.

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. 

The wind yesterday did a number on the snowpack. All aspects and elevations were affected. The most noticeable problem was the large drifts that formed across the landscape. They were not touchy, but if one popped off, it would carry a lot of volume. The secondary problem caught me by surprise. We stopped and dug on a NE facing slope around 7,800 ft. - north of Texas Meadow. HS was roughly 150 cm's. The wind slab on the upper portion of the snowpack did not produce unstable test results but got 2 ECTP's on the basal facets. 

We spent the last two days in the Centennials. On Wednesday, we rode up to the vehicle shop, into Yale drainage, over to Hellroaring, and across the backside to the East Hotel Creek overlook. On Thursday, we went to our weather stations for repairs and visualized much of the range from the top of Sawtelle. 

Day one focused on snowpack analysis as it was lightly snowing for most of the day S- -1 with 2-3" of accumulation throughout the day, and we did not have much for long-distance visibility. We triggered two collapses in a creek bed when someone (I) was stuck while riding toward East Hotel. We were able to see the smaller avalanche paths along Yale and the only slide was a R1, D1 cornice collapse. We dug on a north-facing slope at the pass over to Hellroaring Creek. The facet layer of concern is now buried a meter deep (4F+ hardness) with an ECTX on this layer. Total HS of 155 cm. We got ECTNs 14-29 on the three rain crust layers formed during the last storm cycle.

The south-facing pit overlooking East Hotel was a bit shallower, 125 cm HS. ECTP30 on a crust facet combo mid-snowpack and an extra-curricular ECTP31 on the facets that we have been primarily discussing this season. 

On day two, we got up high, overlooked many avalanche paths, and saw only the slide that Randy Gravett (Rescue Randy) had previously reported in Mt. Jefferson Bowl. 

The collapse and the snowpack structure indicate the potential of triggering an avalanche, but the likelihood has gone down. Given the depth of the weak layers, I am not confident that the snowpack assessment will provide full and accurate information. If folks are starting to push into avalanche terrain, my emphasis is to stick to paths that are less likely to avalanche (sheltered from the wind and less steep) and paths that have lower consequences (smaller slopes with clean runouts). As always, safe travel practices. 

If people don't want to mess with the uncertainty of avalanche terrain right now, conditions are fantastic on many slopes less than 30 degrees. 

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.

OVC with 10k cloud ceiling in the morning (S-1) which cleared to BKN high clouds by 1pm. No signs of wind transport from the previous 24hrs (tree tops holding snow, little/no snow surface clues at the prayer flags and below). 

We took a quick look at the upper ~1m of the snowpack: generally non-consolidated fist-hardness snow. Small, dry-loose slides were observed in Going Home Shoot and on the west facing wall of Middle Basin. We were able to move the top 5-10cm of snow in short, occasional sluffs but did not experience any other signs of instability. No other signs of avalanche activity could be spotted in the area. By 3pm, wind on the summit of Lone Peak was transporting lots of snow.

Went climbing in the greater G1 area yesterday. Pockety slide paths and gullies near G2- Hangover were starting to cross load. Slab formation was just beginning (surface cracking and notable propagation.) Slabs did not have the volume to be consequential, yet. There is a lot of AST (thigh deep trail breaking places). These lower elevation paths are often relatively benign since they are generally well protected. A little bit more wind and slab formation could create hazardous travel in this areas with unforgiving runouts. 

Debris piles from recent DL and likely SS avalanches were observed under cliff bands and gully features in the area that have likely run naturally throughout this storm cycle.

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

Wind slab around 3-12" deep. NE aspect at 8,000 feet. Occurred sometime on January 8th.

On 01/08 my partner and I skied into Frazier basin in the northern Bridgers, we skied the love chutes east down and overall the descent was pretty wind hammered from a downward wind. Once at the lake we took the Frazier return route where we found much better ski conditions in the corridor and decided to lap some of the features. We ended up triggering a small wind slab at around 8k on a NE aspect that broke about a foot deep and ran about 25 yards. Very dense wind slabs were forming on a lot of the aspects getting out of Frazier and we opted to not test our luck any further for the day. 
 

thanks for all the hard work this season GNFAC

Traveled out the North boundary of Bridger Bowl to Texas Meadow. S1-2 from 1030-1200. S2-3  from 1330 until we ended our day (1600). Moderate to Intense snow transport observed NTL. Loading observed on N & S aspects due to swirling and inconsistent winds. Total snow accumulation of 4" observed during our time in the field. Observed two natural avalanches in steep terrain above Texas Meadows, likely released during periods of high PI combined with wind (SS-R2-D1-N).

Skied south of Cooke today and noticed a large natural avalanche just north of the South Siren. N-R2-D2.5-O. It wasn't fresh and likely ran during the last storm cycle. 

We dug on an east aspect at 9800', ECTX, HS150. No cr, co.

As my elevation increased, so did the wind. Heavy gusts were moving snow. Clouds were visible and moving fast above Bridger Bowl and Ross peak. Ross Pass was visibly wind scoured. 
 

I didn’t observe any natural avalanches in the steep terrain along the ridge between ski area northern boundary and Ross peak, but did notice some ski tracks (I believe in the “Trident, Dog Leg chute”). 

We rode into the Taylor Fork today to check out conditions after the new snow from the last two weeks. We traveled up to the weather station above Sunlight Basin, along Sage Basin to the the Beaver Slide, and through Carrot Basin to the wilderness boundary. 

No cracking or collapsing was noted today. We did note two small avalanches along the Carrot Basin headwall from sometime in the last two days that broke on weak snow near the ground. These areas looked to have a shallower snowpack. Besides old crowns previously reported, and these two slides, we did not see any new avalanches in the area. 

Near Sunlight Basin, we performed a snowpit test on an east aspect at 9480' (HS 98). It propagated (ECTP11) on weak, faceted snow near the ground. Our second pit, at the wilderness boundary, was on a south aspect at 8840' (HS 122). It propagated on weak snow below a melt-freeze crust near the ground (ECTP24). 

With blue skies, sunshine, and a lack of cracking and collapsing, it was easy to be lulled into a false sense of confidence about our snowpack. But with a loading event ending only yesterday and our unstable test results, we chose to reign in our enthusiasm, follow a conservative travel plan, and stick to riding lower-angle powder. 

Fresh snow had fallen the night of Jan 6th and through the morning on Jan 7th, about 4-6” of low density snow above 8000ft. No wind or recent drifting was observed. New snow from the past storm was 3-4ft deep, basically comprising the entire snowpack, the avalanche failed on a layer of depth hoar at the base of the snowpack.

As I made my way up toward emigrant peak I observed a very large natural avalanche that ripped out on a NE aspect at 9500ft. It propagated hundreds of feet wide and ran approximately 1500ft. The deepest part of the debris pile was ~15-20ft deep. The crown was approximately 3-5ft deep, maybe deeper. 

Observed several large collapses and whoomphing as I toured around the area. I observed at least 4 other natural avalanches in the area, not as big but still a tell tale sign to have cautious route finding and avoid slopes steeper than 30 degrees in this mountain range. 

Observed one avalanche in the steep chutes just outside the N Bridger Bowl boundary, SS-R2-D1-AS

HS between 150 and 200 cm. 90-120 cm of storm snow over firm mid Dec layers over facets. 15cm from the last few days. Some wind transport at mid elevations with lots of W wind up at ridgetop throughout the day. Much windier than expected in Bradley Meadow with moderate winds swirling from N and W. Sky was BKN and, no new snow. Temps around 10F.

Group from Wisconsin spotted 3 very fresh avalanches today. 2 for them near Red Canyon and 1 near Whites Peak. No other info. Might get photos tomorrow. 
 

2 other slightly older slides spotted

Skied north of Cooke today. The light wasn't great, but I think there is an older avalanche on the east face of Miller Ridge in steep terrain. Could barely make out a crown line near the ridge and old debris on the apron. Maybe it ran 3-5 days ago? No cr, co and the winds were light out of the W-NW, moderate at ridge tops. We picked up 8cm of low density new snow overnight, plus an additional 1cm throughout the day today.