Snow Observations List

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.
 

1 to 3 inches of new snow on top of a very hard base nearly every where with evidence of past wind affect. Condition were Sunny with calm winds and temperatures in the single digits. we saw no avalanche activity cause by snowmobilers or people actively skiing the Hollywood wall. Lots of people around.

It was a beautiful, cold, clear-few, morning with very little wind. 

HS ~140cm on an E/SE aspect at 7500'. HN24 of ~10-20cm between 7500-8500'. HN is light and unconsolidated with no evidence of wind transport. A thin, breakable MF crust was observed in similar elv. bands in east-facing trees below the new snow. Two hand shears had planar results on this layer but snow above the crust did not have slabby characteristics. No cracking or collapsing was observed. L-ASc-R1-D1-I sluffs occurred while skiing.

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. 

We rode out Buck Ridge, through Second Yellow Mule, around the top of Third Yellow Mule, and through the top of McAtee. Snowed average S1 all day until 2pm when we rode out, and was still snowing up high at that time. Wind was light from the north. Minimal drifting and transport in the morning, but some very shallow, very soft slabs cracked on wind-loaded slopes near the ridge. Avalanche activity was limited to very small F- dry loose and some F- 2-4" soft slabs. Visibility was not great though. Natural and triggered by us on small test rolls.

There was 4" of new snow on average, and up to 8" of low density snow in places. Below today's snow there was 1-2" of snow from earlier in the week, and that was on top of a layer of surface hoar in some places or soft facets in most places.

The primary concern was and will be where the recent snow gets drifted into thicker or stiffer slabs. Recently buried weak layers might make these fresh wind slabs easy to trigger initially, and possible to trigger for longer into next week. Where today's new snow was not drifted there was minimal hazard aside from small dry loose avalanches.

We dug on an E facing slope at 9,400'. HS was 155cm and we had an ECTN12 on the surface hoar layer at 130cm above the ground.

Very touchy storm slabs formed throughout the day. 6-8” deep by 3pm. low density snow/slab but very fast moving. We were able to trigger steep (35+) rolls with chunks of ice and even got one to go with a falling rope. We saw one natural (d1) that ran ~200’ down a gully near mummy 2. 

We went to Lionhead seeking some of the thinnest and weakest snow. We found relatively thin snow - the snowpack was mostly a 1 meter deep (3.2 ft). It was supportive for sleds and you could walk on top with about 6-8 out of  every 10 steps not punching through to the ground. This is because there is a very cohesive slab on top of the early December facets.

What surprised us was how stubborn that weak layer was in our tests. We dug in 4 different places on E, E, E, and NW aspects between 8000 and 9200 feet. ECT's either wouldn't even break or would propagate on the weak layer after mid to high 20's for taps.

We observed some new facets near the snow surface that formed last weekend during very cold weather. On Lionhead Ridge we found these facets capped by a hard but thin (~4 inch thick) wind slab. 
 

Summary

• The early December faceted layer seems mostly dormant for now.
• Wind slabs are the main problem and they will be extra sensitive as more snow comes Friday providing winds more ammo to make the wind slabs deeper. Because these wind slabs may be resting on facets, they could stay a problem for sometime.
• We did not get a chance to map how widespread or isolated this wind slab/facet combo is.

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. 

From email: "Skies were clear at 8am, but clouds rolled in quickly and we had S-1 snowfall starting at 1pm. Winds were L in the basin and L-M at ridge tops out of the W-NW. Moderate snow transport on high elevation peaks. West aspects near ridgetops were scoured, as they usually are. We found a 2-3cm thick MF crust under 5-10cm of new snow on E, W, and S aspects near ridgetops and in the basin. No cr, co.

Students dug pits on E-SE aspects at 9200', as well as on E and W aspects near the Prayer Flags. HS ranged from 100-145cm. Two of ten pits had propagation. ECTP1 on small facets above the MF crust and under a wind slab. ECTP30 on 2mm facets 30cm up from the ground. Hand pits had planar results below the MF crust where it was capped by a wind slab." 

I toured up to the Divide Cirque today, and found some quality riding on SE, E, and NE aspects. 

I saw evidence of a recent car-sized cornice fall on an E aspect. The resulting dry loose ran far, but saw no crown or evidence of a deeper avalanche. 

Also noted a recent natural wind slab avalanche below ridgeline on a SE aspect at 9800’. It was around 60’ wide and ranged from 2-6” deep. 

The clouds came out just in time, before the sun began to have any effect on solar aspects. Saw active wind transport over by Hyalite Peak, but it wasn’t as bad over in Divide.

We rode to the motorized boundary and toured up the shoulder of the Throne, poked out to the north-facing runs at the top, and then moved to the south-aspect gully from the upper saddle. 

Winds have worked over many slopes near the Throne. We found some slopes stripped nearly to dirt with the snow blown off to who knows where, and others had wind-sculpted sastrugi. Trees were broken off, and debris littered the snow surface. We probed for snow depths. On the east face, depths ranged from 20 cm to 100 cm on the shoulder (we may have missed deeper spots). At the upper portion of the north-facing run, we found 50-75 cm depths. The south face had a 115 cm depth.

There was some isolated wind-loading mid-slope. We saw one old crown that was nearly drifted in on a steep break over at mid-elevation on the east face. 

Somehow, we found a slope sheltered from the wind's effects. Because the danger is low on non-wind-loaded slopes, we considered traveling down through avalanche terrain. Before we did, we assessed stability to give us one last chance to turn around, and we followed safe travel practices, exposing one skier at a time to potentially hazardous terrain.

Today, we traveled into the Maid of the Mist basin and up and along the Palace Butte ridgeline.  Although temperatures have warmed up significantly since the weekend, strong winds kept conditions frigid. Winds blew plumes of snow off the high peaks and at ridgelines, gusting 50-60 mph. Even at low to mid elevations, spindrift was blowing off of cliffs, snow was blowing out of trees, and the surface of the snowpack had been affected by wind. We found stiff, hardened surfaces and sastrugi starting around 8800', nearly 1000' lower than the tops of the surrounding ridgelines. 

Most of the high elevation snow has been transported already. Up high, snow surfaces are hardened and we were mindful of wind slabs that have formed in the last few days. 

On a north facing aspect at 8800' we got an ECTP 22 in our pit test on a wind slab over softer snow. We also dug on a south facing aspect and found new snow on top of a melt-freeze crust and small faceted grains. This crust likely formed during the warm temperatures before the cold spell last Thursday (1/16).  

We heard one collapse on a heavily wind-loaded pillow of drifted snow, but beyond that, the only other sign of current instability was the active wind loading itself. 

We chose to avoid traveling on slopes steeper than 30 degrees that had signs of wind affected snow (textured snow surfaces, stiffening of surfaces, and obvious wind pillows). Slopes that had not been affected by wind held the safest and highest quality riding. 

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. 

Very reactive wind slabs developed overnight. 6-30inches thick. 

Wind loading on all aspects due to swirling winds. Cracking about 3-12” thick around top of wolverine forest. No signs of persistent slab instability, deep snowpack throughout.

From FB message 1/19: "In between redstreak peak and white peak... The whole slope cracked...  the one I stopped on I put my leg in the crack and went to my knee inside the crack"

Screenshots from videos sent in messenger

Snow depth 160 and generally stabile conditions with the lower layers gaining some strength at this location. ECTX x3 in this area. Old wind slab observed in the area but no signs of instability on that layer. 

Wind was swirling in Maid of the Mist yesterday, mostly upslope winds that were transporting snow, but inconsistently and were difficult to predict where they were loading. We did not find widespread wind loading, but did get a very small windslab to release just below the top of the ridge (max 3-4" thickness, see image).

ECTP22 at 20CM. Bottom layer is a high concern to me. We experienced whumphs the entire walk in from the parking lot and had a pretty sketchy time attempting to ski a glade directly above fairy lake. The refrozen snow above the weak layer also adds some false security at a glance.