Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
View on map

Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
Open full map
Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The combination of recent snow, wind, and buried weak layers make human triggered avalanches possible today. Cracking within wind drifted snow and audible collapsing of the snowpack are signs of instability. Carefully assess the snowpack before entering steep, rocky terrain, especially above or below large cliff bands.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Persistent slabs that are 2-4 feet thick exist at the upper and middle elevations. These slabs sit on top of weak snow that was buried dating back to the end of November. No avalanches on the November 27th layer have been observed with the most recent loading event, but layers of less developed facets exist closer to the surface of the snow (buried on December 5 and possibly later). It remains uncertain whether any of the most recent avalanche activity associated with the "Bomb Cyclone" actually failed on any of these layers. 

    The November 27 layer is now buried over a meter deep at the upper elevations and is certainly stubborn if not unreactive, especially on northern aspects. Possible exceptions could be avalanche paths that slid on this layer during the early December cycle, especially at the middle elevations. Southerly and Easterly aspects at the upper elevations seem to have the best slab/weak layer combinations for avalanches to occur. Areas where wind slabs sit on top of persistent weak layers are of primary concern, especially in and around large cliff bands. 

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Wind slabs that around 1 foot thick exist at the upper elevations. These slabs are left over from the storm on December 20/21 and are stubborn and unlikely to propagate very far at this point. Steep unsupported terrain in and around cliff bands are of primary concern. Very steep convexities are other possible trigger points.  Extreme winds associated with the most recent storm created unusual distribution patterns, with lots of snow ending up well below traditional starting zones. 

Avalanche Discussion

Yesterday was mostly cloudy with valley inversions and light snow showers in the Tetons. In the last 24 hours 2-5 inches of snow has fallen in the Tetons and Rendezvous Summit received a grand total of 416 miles of wind out of the WSW. Temperatures are currently near their maximum values for the last 24 hours and range from the mid teens to lower 20s. 

Frontal passage from the "Bomb Cyclone" event happened around 72 hours ago at this point. Since that point in time temperatures have been frigid (currently on the rise) and winds have been relatively modest. Natural avalanche activity likely ceased within a few hours of frontal passage on December 21st. No human triggered avalanches have been reported in the Tetons during the last 3 days. 

The "Bomb Cyclone" from December 20/21 dropped around 12-15 inches of snow and a little over 1 inch of SWE at the upper elevations in the Tetons. Fierce winds associated with frontal passage on the morning of the 21st caused a natural avalanche cycle. Natural avalanches were observed in the side country surrounding both Jackson Hole Mountain Resort and Grand Targhee Resort. Naturals were also reported in Grand Teton National Park and the Teton Pass area. Many of these slides seemed to have decent propagation but likely failed on interfaces above the November 27th layer (with many failing on non-persistent interfaces). Most of these avalanches appeared to be size 2 avalanches (~2 ft deep) on south and east aspects. 

The extreme winds from December 20/21 caused abnormal loading patterns, with much of the snow ending up downslope from traditional start zones. Aprons below complexes of large cliff bands are areas of  concern, as are mid slope areas on south and southeast aspects that may have been cross loaded. Unsupported slopes and very steep convexities in rocky terrain are also areas that should be evaluated. 

The November 27th layer appears to be largely dormant at this time with no avalanches observed on this interface from the most recent loading event. Upper elevation south and east aspects in and around rocky terrain are still suspect. Other persistent weak layers exist in the snowpack above the Nov. 27 layer, but they are less well developed and their distribution patterns remain uncertain. A layer buried around December 5th keeps showing up in snow pits but it is not showing much of a propensity to propagate.

 

 

Regions covered