Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Human triggered avalanches are possible at the middle and upper elevations, especially where recent snow and wind have combined to form cohesive slabs of snow. Steep and rocky areas that have been wind affected on north through east through south aspects are the most likely areas to trigger a slab. Monitor the sun's influence as well as the wind direction today, and pay attention to signs of instability such as cracking within drifted snow. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    Wind slabs (both soft and hard) are possible at the upper and middle elevations today, with depths from 1 to 2 feet. 

    Up to 18 inches of snow has fallen at the upper elevations in the Tetons over the last 4 days. This snow has largely been low density and is readily available for transport. Monitor the wind direction and look for blowing and drifting snow. 

    Loose snow and slough could be an issue for skiers and riders in "extreme" terrain. The new snow could also form into very shallow surface slabs just from settlement and the influence of the sun today. Be mindful of roller balls and other signs of instability in very steep southerly terrain. 

    (1/4/2023)

    The crown of this wind slab was up to 30 cm thick and was intentionally triggered near a ridgetop @ 9k' in the Tetons on Wednesday. 

Avalanche Discussion

Weather Synopsis

The Tetons have picked up 1-4 inches in the last 24 hrs, with the Greys picking up around an inch and Togwotee receiving 1-2 inches. Winds have been light to moderate at ridgline, with average speeds in the 10-15 mph range and directions out of the S through W. In the last 4 days the mountains of western Wyoming have picked up 6-18 inches of snow with light to moderate winds.

Yesterday's atmospheric circulations were somewhat strange, with western Wyoming sitting in between stronger flow to the north and south. This allowed for small scale orographic effects to dominate, resulting in variable new snow amounts throughout the Tetons. A weak trough began to impact western Wyoming on January 5th. Prior to this the forecast area was under primarily NW flow as a closed low system sat over southern Minnesota. This resulted in favorable Teton Trickle conditions and an abundance of low density (blower) pow.

A weak ridge is in place for the time being but it won't last long. The next pulse of moisture looks to be showing up  Sunday night into Monday ahead of a larger trough.

Recent Avalanches

The most recent natural avalanche cycle followed on the heels of tropical moisture in a SW-W flow that hit the Tetons from December 27- January 1. Human triggered avalanches have been reported more recently and have involved more recent snow and sensitive wind slabs.

  • Peaches- 20230104, SS-ARc-R1-D1-S, N aspect @ 9000'
  • Eddington Canyon, Y chutes-20230102, SS-N-D2.5-O, W aspect @ 9200'
  • Martini Chutes- 20230102, HS-N-R2-D3-O, SE aspect @ 10400'
  • Horseshoe Bowl- 20230102, SS-N-R1-D2-I, SE aspect @ 9200'
  • Ullr 2- 20230102, HS-N-R2-D2-O, SE aspect @ 9500'

Snowpack Summary

Current snow surfaces are composed of low density snow that has settled with some graupel from January 5 mixed in. In wind affected areas the surface of the snow has turned into upside down wind slabs. 

Wind slabs seem to be extremely isolated at the middle elevations at this time. South aspects at the middle elevations could see some influence from the sun today, but probably not in the form of wet-loose activity with the given temperatures. The new low density snow from the last few days could settle into shallow soft slabs that could run on density breaks or crusts.  

Snow depths are approaching 2 meters at upper elevations in the Tetons. The top half of the snow pack is composed of new, decomposing, and wind packed snow. The bottom half of the snowpack contains various faceted layers of snow that formed in early December, mid-late November, and October. The November 27th layer is probably dormant at this time and unlikely to resurface without an extreme loading event and only in very isolated areas (see Martini Chutes avalanche).

The low elevations have new snow on top of a rain crust that capped the pack below 7500' on December 27.

 

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