Snow Observations List

I rode into Lionhead head with Ryan, Aaron, and Omar on an avalanche warning day. We went straight to Ski Hill and dug a pit there. With better visibility than I anticipated we dropped down to Denny Creek, travelled up and around to the head of Targhee Creek before dropping down through Targhee and back to the vehicles. During the day ~6" of snow fell with moderate winds. Wind slabs were widespread as we rode, and the surface conditions had stiffened in many locations due to the effects of the strong to extreme winds. 

We saw many R1-R2 wind slab avalanches below the cornice line. Visibility was limited so I won't estimate the exact number, but nearly every time we had good views of the steep faces, we saw cornice collapses, debris, or small crown lines. There were two slides on east aspects that ran closer to full path and piled debris more deeply. I expect that most of these had run within the last 24 hours, but continuing snowfall and hurricane force winds made precisely dating these a challenge (many trees were blown down during the wind event, these too were already somewhat buried). None of the avalanches broke on persistent weak layers as far as I could tell. 

We dug at Ski Hill. Pit results were unremarkable with an extended column test breaking and propagating with an extracurricular ECTP32 on the January facets. The January weak layer was buried a meter deep and was 1 Finger Hardness and had gained strength. However, we wrapped around the corner on our decent and found a shallower slope (1m deep) where Fist Hard facets were capped by a dense wind slab. I did not perform an official ECT, we had undercut the slope with our sleds and were able to knock 5-foot-wide sections of slab off with an arm chop, triggering miniature avalanches that slid easily. This showed us what we needed to know--an avalanche on a steep slope with that structure was likely (see video). 

Not much snow on storm castle road until 5500 feet, started snowing at about 6500 feet, wind didn’t start blowing from the south until after 12:00pm Got CT5 on a layer buried 8cm on a North facing slope at about 7200 feet, Another layer broke after just above the ground at CT23. Snow depth was 110 mm. 

We rode into Tepee Basin and to the north wilderness boundary. It was snowing all day with moderate winds and some strong gusts in more open areas. We could only slightly see the bottom of some avalanche path, but did not see any signs of avalanches (there could have been some higher up in terrain obscured by clouds.)

There was 1.5-2 feet of new snow that fell since Thursday. We dug (3) snowpits on northeast, north and southeast slopes, between 8800'-9200'. The pits on northerly slopes had ECTP 17 and 22 on a thin weak layer below the new snow. We also had ECTP 6 within the storm snow.

There was minimal cracking across the surface in the new snow, but plenty of signs of fresh drifts. It felt likely you would easily trigger storm slab or wind slab avalanches on steep slopes.

From email: Isolated wind slabs today in the southern Bridgers.

Up to a foot of soft snow which seemed to have included a few inches from last weekend. Winds were transporting snow across Buck Ridge all day long.

We triggered two small and shallow wind slabs that didn't go anywhere, but they were a warning of bigger wind slabs on bigger slopes. We didn't find any faceted or weak layers of concern deeper in the snowpack. 

Wind slabs will grow in size overnight and will be the main concern tomorrow. Fortunately they will be easy to see an avoid.

Toured into Margaret's Meadow this afternoon. 2" of dense snow over a 1/2 of graupel, on top of a wind crust. Light winds from the SSE. Light wind loading on the N, and NE aspects. No cracking or collapsing, and new snow seems to be bonding (at leas on lesser angled slopes). Skiing conditions were  surprisingly good.

Today I triggered a D1 dry loose avalanche on a E facing 35 degree slope, 9300 ft on Mt Henderson. The new snow is very low density and is not bonding well to the old interface. I also observed some more dry loose activity/small wind slabs on Sheep Mt, NE facing, 10400 ft.

We looked at the avalanche in Sunlight Basin/Taylor Fork that was triggered by a snowmobiler yesterday. It was 50' wide, 100' vertical, 2-3' deep hard slab with 8-9" new snow on top. Broke on weak facets buried in late January. Dirt layer from Feb 4 was visible 6-8" above weak layer. Bed surface was 3" to 1.5' deep of weak, sugary facets. Slope angle was 38-40+ degrees. 8800', WNW aspect.

We also rode to the northwest end of Carrot Basin near the wilderness boundary and dug a pit. Snow depth was 5-6 feet. We found the buried weak layers 3 feet deep. It broke and propagated with many extra hits after an ECTX. 

Snow fell lightly most of the day up high while it was sunny in the parking lot. Wind was light with a few moderate gusts. There was minimal signs of recent wind, but forecast is for wind to increase and there is a lot of light snow to drift into slabs.

We traversed the ridge south from the Bridger Bowl ski area boundary to Bridger Peak, descended a NE aspect and skinned/traversed back to the ski area boundary. Moderate west winds weren't transporting a significant amount of snow (much of the west side of the ridge was already scoured bare and the remaining snow was already hardened). The sun and clouds were in and out through the day and there were even a few snow flurries, but no accumulation.

Wind Slab avalanches were our primary concern today, but we did not see any as we traversed the ridge and the new snow we encountered was not cohesive.

Dry Loose avalanches (sluffs) ended up being the biggest hazard we encountered. The new snow (approximately 8") was easily sluffing over last weeks crust and was entraining significant volume and running far in steep terrain. It had plenty of power to knock you over or into trees/rocks. 

We saw no slab avalanches or signs of instability.

Winds in the Frazier Basin zone were stronger than expected with moderate to strong gusts at the ridge, increasing through the day. 
 

Light flurries <S1 through the morning increasing to S1 by the time of our exit. Tough to gauge accumulation due to the wind but would guess 2-3cm total through the day. New snow from yesterday and today is generally not well bonded to the underlying surfaces which range from windboard, supportable crusts, and old wind slabs depending on aspect/wind exposure, and this made for challenging uphill travel at times. 
 

We noticed two large windslab pockets that had released since yesterday’s snow. One at the base of Hardscrabble Peak on a N aspect, the other in one of the SE facing gullies that access the Peak 9299/Hollywood Headwall ridge (see photo). 

Found 5-8” of fresh low-medium density snow. Triggered multiple small soft storm slabs/sluff which occurred on steeper slopes (40+ degrees). 
also noted an interesting crust overlaying a weaker layer that the new snow sat on. This crust wasn’t found everywhere, but just on the sides of rolls facing west or north west (between 9000’-9400’). When probed with a pole it sounded hollow. The crust was thick in nearly every place we found it and didn’t ever collapse under us, but it did shear in hand pits. A thin layer of graupel was also on top of this crust in some areas. 
other areas where this crust didn’t exist seemed to either not have refrozen completely before getting snowed on, or never got above freezing in the first place (high elevation north facing). In some areas the new snow bonded very well, in other areas it was easier to get it to sluff off the old crust. Attached is a quick photo of the crust location and the weak snow below it. 

Toured up the south end of Miller Ridge to 9,500'. Dug a pit on a northeast facing slope, 9300' (profile and pic attached). Snow depth was 7-8 feet.

6" of new snow was right side up. Below the new snow was a soft (1F-) melt-freeze crust with soft decomposing and slightly faceted particles below. ECTN13 broke below the crust. Below that the snowpack was 1F to P+ hard and lacked weak layers. The Feb 4 dirt layer was clearly visible.

There was a small natural dry loose on south face of Crown Butte and I triggered a dry loose slide on a test slope near the ridge (video). Wind was calm, even along the ridge near regularly wind-loaded slopes, and there was no snow blowing off ridgelines. I saw no signs of fresh wind-loading, but when the wind blows there will be fresh drifts that will be possible to trigger.

Skies were broken to partly sunny with a few light snow showers. Slopes that received sun got moist at the surface (at least below 9,000').

A group of riders saw Mark at the gas station and shared that they had triggered a 4' deep slide in a small pocket in Sunlight Basin of the Taylor Fork area. It was in an area with a relatively shallower snowpack, and broke on weak snow near the bottom of the snowpack. The rider that triggered it was going uphill and got stuck shortly after and noted the snowpack was much deeper there.

Today I observed multiple small wind slab avalanches off Woody Ridge. NE and E facing, 10000 ft. Max size D1. Also, there was many dry loose slides on Cooke Peak in Hayden Creek.

We rode to the top of Sawtelle to de-rime the anemometer (wind sensor) and then down into Rock Creek Basin under all the big north facing avalanche paths.

Key findings:

1. New snow amounts ranged from 6-8" at lower elevations and 18" at higher elevations
2. We did not observe any cracking or collapsing on non wind loaded slopes.
3. We observed two very recent natural storm slab avalanches about a 1.5 feet deep. One of them entrained a significant amount of snow an ran a long ways.
4. There has been minimal wind effect except at ridgetops
5. Extended Column tests on north facing slopes continuously broke and propagated after 12 taps (ECTP12) just under a soft crust in snow that fell last weekend. These appeared to be breaking on broken stellars/snowflakes. On other aspects, the crust was much thicker and harder.

Conclusions:

The likelihood of triggering a soft slab avalanche about 1.5' deep seemed low on non-wind loaded slopes. Any amount of wind affecting a slope whether loading a slope or just stiffening the new snow, dramatically increased the odds of triggering a slide. We felt comfortable riding in avalanche runout zones and even climbing into the paths some. The main strategy was to stay out of the upper starting zones that are steeper and have seen some wind. HOWEVER - we carefully limited our exposure in big runout zones where a falling cornice could have triggered a slide that could have crashed down onto us. We did not think that we would trigger an avalanche from below  

Looking ahead  - Strong winds Sunday through Monday will have plenty of snow to transport along with additional snow that will fall. This should increase the danger and the size of possible avalanches.

From phone call:

Kevin took a group into the Centennials.

8" of new snow at 8000'. Surface crust below the new snow was 3 CM thick. There was a facet layer below crust that was concerning. ECTN3 below crust. 

Kevin found the January facet layer 90 CM down (4F hardness) a couple miles north of White Elephant at 7800-7900' (0.5-1mm size). No results in tests but was concerned about their activation if the storm snow start stacking up.  

He noted that the Wind Slab and Storm Slab problems are growing. He saw shooting cracks in the new snow, several feet in front of his skis. 

Winds were light to moderate but gusting into the 20s mph. 

Went up to Beehive Basin to check out the new snow as it was falling ---- but it wasn't, yet (between 10 am and 1 pm). There was a dusting of new snow when we arrived at the trailhead and a few flakes fell during the couple hours we were up there, but the substantial accumulations hadn't started. In fact, skies were mostly clear during our tour.

We skinned up the west facing sub-ridge to the Prayer Flags and descended via the Going Home Chute. Surface conditions were rough on any slope that wasn't shaded, with stout melt-freeze crusts. There was still a tiny bit of old, soft snow present in the shade.

No signs of instability or recent slab avalanches noted (we did see some older, wet loose slides).

Danger was LOW, while waiting for the storm to start in earnest.

The winds were strong enough combined with the higher humidity snow that pinwheels were actively forming and moving on flat to slightly downhill terrain. I hadn’t seen this often, so I thought it was worth sharing. 

Toured into Texas Meadows this morning. No avalanche activity seen, no cracking or collapsing. Northern aspects and higher elevations holding better snow, without a wind or sun crust.

Rode into Fairy Lake and skinned up the east shoulder of Naya Nuki. Winds went from strong to extreme out of the south in the early afternoon and were absolutely hammering. Despite the crazy winds, there was really no snow left to transport, so there was no active windloading. Wind surfaces were highly variable, from sastrugi to windboard to meltfreeze crusts to protected powder in the trees.

Saw no signs of instability or recent slab avalanches. We did see a good bit of wet loose activity that likely happened a couple days ago.