Trip Planning for Island Park

as of 5:00 am
Dec 92″ | 20-40 S
Dec 8 0″ | 10-30 NW
Dec 7 0″ | 30-50 NW
9885′     12/10 at 01:00
4.1℉
W - 40mph
Gusts Unknown mph
8750′     12/10 at 01:33
69.4″ Depth
2.6″New
7710′     12/10 at 01:00
15℉
56″ Depth
Bottom Line: 4-8” of new snow are possible in the Island Park area during the day today. There is weak snow buried 2-3 ft deep in the Lionhead area (and it likely exists in the Island Park area as well) that could avalanche under the weight of a skier or rider today. Dig to search for and test these weak layers in the middle of the snowpack before riding steep slopes. Also watch for fresh drifts forming today as new snow accumulates, if it’s drifted more than a few inches deep you could trigger a dangerous slide. Dave and I are headed to the Island Park area today. Visit the Island Park Trip Planning page tonight to learn what we find, and watch our field video.
Primary Problem: Persistent Weak Layer

Snow Observations- Island Park

Island Park
Yale Creek
Lots of new snow, wind drifts, and facets in Yale Creek
Snow Obsdrvation includes images
Snow Obs contain video

Snowed hard all day. Lots of new snow (18” in the past 24 hours at upper elevations at 4 pm). Found 4 ft deep fresh wind drifts near the summit of Sawtelle Peak while going to work on our weather station. 

Rode into Yale Creek and dug on a south facing slope at 8000 ft. HS was 133 cm. Found 2 mm facets 40 cm off the ground (similar to what we’ve been seeing in the Lionhead area). Interesting to note that on this lower elevation sunny slope there was a melt-freeze crust above the facets and percolation columns running down into the facets. ECTP25 on the facet layer. As we rode to the head of Yale Creek the new snow kept getting deeper until there was ~18” of new snow where we dug again at 9000 ft on a NE aspect. HS was 235. ECTP8 and ECTP9 within and at the bottom of the new snow. Lower snowpack looked pretty decent and there wasn't a dramatic faceted layer. Rounded facets in the bottom meter, but 1 Finger hardness and no results in the ECT. 

All this new snow and wind drifting makes for unstable conditions. More snow this weekend will make the avalanche conditions even more dangerous. Finding weak layers in the snowpack means that avalanches could break deeper, could be triggered from below, or could be triggered after multiple people have ridden the slope. 

We recommend avoiding steep terrain and the runout zones below steep slopes for now.

Full Snow Observation Report
Island Park
Arange Peak
Good stabilty, but weak layers are concerning.

The snowpack turned out to be more stable than I had expected. 90cm at elevation with descent cohesion. 10cm of new snow. Compression test resulted in a CTN. Extended column test resulted in ECTX. I am still wary of some wind loaded drifts that could crack or collapse but didn't find any. There is a weak faceted layer about 20cm down that could become a problem with a new load of snow.

90cm at elevation with descent cohesion. 10cm of new snow. Compression test resulted in a CTN. Extended column test resulted in ECTX.

Full Snow Observation Report
Lionhead Range
Lionhead Ridge
Lionhead ECT results and obs
Snow Obsdrvation includes images

ECT Test Results

Location: 300ft below Lionhead Peak

Elevation: 9250ft

Aspect: East, 88deg

Slope Angle: 33°

Total Snow Depth: 115cm

Result: ECT 22, at 15cm deep (new snow interface).  At this location the top 10cm of new snow was loose, then 5cm of new snow formed into wind slab.  Remaining 100cm of snow ECTX, well consolidated, no visible layers, approx 2F hardness to the ground.  

Comments: Failure at the new snow interface seemed very spatially dependent.  We had an ECT 11 in another area. 

Skied multiple locations along Lionhead Ridge over 3 days, NE to E aspects.  Our observations were in line with the avalanche reports.  New snow was generally 15cm deep and weakly bonded to the existing snowpack.  There was minimal wind transport during this time along the more protected NE aspects along the ridge line, so the snow was not particularly wind loaded or consolidated.  Even so, there was multiple instances of small natural loose snow avalanches on steeper aspects or terrain rollovers.

 

Full Snow Observation Report
Island Park
Reas Peak
Wind slabs cracking on Reas Peak
Snow Obsdrvation includes images

A snowmobiler noted cracking of the snow surface on the south face of Reas Peak out of Island Park. The wind crust was 3-4" thick and had facets underneath which aided the propagation.

Full Snow Observation Report
Island Park
Sawtelle Peak
First Snowpit on Sawtelle Peak
Snow Obsdrvation includes images
Snow Obs contain video

We went down to Sawtelle Peak to do some work on one of our weather stations. Lots of rime on the peak.

While we were down there, we dug a pit to see how the snowpack is developing in the Island Park area. Some wind drifting, but not super dramatic. Dug on an east aspect around 9000 ft off the Sawtelle Peak Road. Snowpack depth was around 4 ft. ECTX results.

It's still early season, but for now we're happy with how the foundation of the winter's snowpack is shaping up.

Full Snow Observation Report
Island Park
Hellroaring Creek
Variable Surfaces-Hellroaring

During the annual setup for the Hellroaring Hut we underestimated the amount of snow based on snotel readings in the area. 18”+ in shaded areas around 7,500’ and < 6”-12” on solar aspects, steep solar aspects were already melting out and bare ground was being exposed. Thick sun crusts we’re already formed on most solar aspects, while shaded regions remained unconsolidated. Lots of surface hoar growth in the meadows. Long story short, it’s good to know the relationship/aspect of the Snotel sites you trust for data mid winter, going forward although wary season snowfall was limited there will likely be some interested surfaces to contend with in the Centennial Range until the snowpack gets deep enough to begin the healing process…

-Sam

Full Snow Observation Report
Bridger Range
Bridger Bowl
Cracking in a drift at Bridger Bowl
Snow Obsdrvation includes images

An observer saw evidence of wind loading creating the conditions for avalanches in the Bridger Range on Sunday. Cracking is an indicator of instability. The observer noted that the relatively small drift he saw was "nothing consequential," but this shows that unstable drifts are forming. They will be more consequential where there is more snow and as the wind creates larger drifts. 

Full Snow Observation Report
Island Park
Sawtelle Peak
New Snow Depth Sensor on Sawtelle Peak
Snow Obsdrvation includes images

Ian and I completed the setup of a SNOdar snow depth sensor on Sawtelle Peak in the Centennials. Located at 8800 feet elevation. The sensor will record total snow depth and 24 hr snowfall. Data will be displayed on our website soon at: http://www.mtavalanche.com/weaterh/stations/sawtelle-snow.

The snowpack is non-existent in this area. I think the only snow I could see was the north summit snowfield on Lone Peak from the drive.

Full Snow Observation Report

Relevant Photos

Displaying 1 - 11
  • From IG 12/3: "It was natural. Happened last night or this morning. It hadn't slid when we left yesterday. We were first tracks in today, and there were no tracks above or below this slide. Crown at the peak was around 6'. Average 2-3' crown. 10' debris piles at least." Photo: R. Malmstrom

  • From IG 12/3: "It was natural. Happened last night or this morning. It hadn't slid when we left yesterday. We were first tracks in today, and there were no tracks above or below this slide. Crown at the peak was around 6'. Average 2-3' crown. 10' debris piles at least." Photo: R. Malmstrom

  • A snowmobiler noted cracking of the snow surface on the south face of Reas Peak out of Island Park. The wind crust was 3-4" thick and had facets underneath which aided the propagation. Photo: Anonymous

  • Big Sky ski patrol triggered these slides with explosives on 11/22 during routine avalanche mitigation work. The avalanches were hard slabs that averaged 12" deep and broke on a weak layer above a crust on top of snow that fell in October. Photo: BSSP

  • Big Sky ski patrol triggered these slides with explosives on 11/22 during routine avalanche mitigation work. The avalanches were hard slabs that averaged 12" deep and broke on a weak layer above a crust on top of snow that fell in October. Photo: BSSP

  • Rimed weather station on Sawtelle Peak. 11/17/22. Photo: GNFAC

  • Observer reported "A number of Avalanche Crowns on an east aspect at 9500 ft." in Tepee Basin.

  • An observer reported "A number of Avalanche Crowns on an east aspect at 9500 ft." in Tepee Basin

  • Evidence of wind-loading creating the conditions for avalanches in the Bridger Range. Cracking is an indicator of instability. The observer noted this was "Nothing consequential," but this shows that unstable drifts are forming. They will be more consequential where there is more snow and as the wind creates larger drifts. Photo: E Smith

  • We completed the setup of a SNOdar snow depth sensor on Sawtelle Peak in the Centennials on Wednesday 10/19. Forecaster Ian Hoyer for scale.

    Located at 8800 feet elevation. The sensor will record total snow depth and 24 hr snowfall. Data will be displayed on our website soon at: http://www.mtavalanche.com/weather/stations/sawtelle-snow.

  • The newly installed Sawtelle Peak weather station. Photo: GNFAC (10/4/2022)