Bollettino valanghe

Snake River Range

Bridger-Teton Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

The avalanche danger will start at moderate and rise to considerable today with warming temperatures, clear skies, and strong solar radiation. Wet snow avalanches will become likely in steep, sunny terrain and could be large enough to bury you. Watch for rollerballs, pinwheels, or slushy snow surfaces that indicate unstable snow. Minimize time spent under large sunny slopes warming in the sun, and seek out cooler, shady slopes. Avalanches could be unpredictable, break wider than expected, and entrain large amounts of snow.

Problemi valanghivi

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Wet snow avalanches will become likely below 9,000 feet in steep sunny terrain as temperatures warm and crusts melt. Loose snow avalanches could entrain large amounts of snow and gouge down to buried crusts. Wet slab avalanches are unpredictable, can break widely, and occur without any warning signs. Avalanches could be 1-2 feet deep where recent snow lies on buried crusts that could behave as slick bed surfaces. Monitor for slushy snow and minimize time beneath large, sunny slopes, particularly those with cliffs and rocky features that warm very quickly. Plan an exit strategy that avoids passing on or under sunny avalanche terrain later in the day. Low-elevation terrain lacks snow but is still exposed to overhead avalanche hazard.

    Old, stubborn wind slabs could destabilize and break on hardness changes with warming today at upper elevations. Cornices will be a concern with warming temperatures and could act as large triggers. Minimize time under steep slopes with looming cornices.

    Watch for rollerballs as a clear sign of warming and destabilizing snow.

    Photo: Bridger-Teton Avalanche Center

Avalanche Discussion

We have entered a thawing event that will last through Saturday and could lead to a significant avalanche cycle. Record-breaking temperatures for March are possible. Wet snow avalanches could become very likely and entrain large amounts of snow. 

Wet slab avalanches may or may not occur today. It would not surprise me if we did not see any until tomorrow or later in the week. The next couple of nights will bring even less of an overnight freeze and increase the likelihood. However, wet slabs are unpredictable during strong warm-ups.  There are several factors at play, some of which contribute to the uncertainty.

  • Overnight freeze - temperatures did not fall below freezing at 9,500 feet. However, mostly clear skies overnight and radiative cooling of the snow surface have led to the formation of crusts at elevations below the freezing line. Underlying snow remains wet in many low and middle-elevation locations. Take note of where crusts exist and where underlying snow is wet.
  • Extent of today’s heating - high temperatures are forecast to reach 40°F at 10,000 feet and near 50°F at 9,000 feet. Clear skies today will allow for rapid heating of snow surfaces starting on east aspects this morning. Surface crusts will thaw quickly. Timing is everything today while moving through the mountains and taking advantage of travel on supportable crusts.
  • Water in the snowpack (source of uncertainty) - this is related to overnight freezing AND the extent of daytime heating, but it is hard to quantify, let alone estimate, how much meltwater it will take to become a problem and trigger avalanche activity. Wet slabs are unpredictable.
  • Interaction with water, a bed surface, and a weak layer - melt water in the snow will eventually weaken bonds between a buried crust and the overlying slab. The tipping point usually happens after the second night without a freeze, but there is some uncertainty and guesswork at play. Just to reiterate, large wet slab avalanches are unpredictable.

Regardless of overnight freezing, daily warming, and uncertainty surrounding water in the snowpack, one thing we know for certain is that the avalanche hazard will rise.

Don’t try to outthink this problem. Give yourself a margin of safety and stack the odds in your favor as you plan the day.

  • Get into and out of the mountains early to avoid peak daytime heating and avalanche activity. Avoid sunny avalanche terrain later in the day.
  • Monitor snow surfaces and look for clues. If you find slushy surfaces or step out of your skis and sink above your ankles, conditions are unstable. Rollerballs and pinwheels are early clues of instability and can indicate potential for larger wet problems.
  • Avoid spending time under steep warming slopes and, when possible, move to shadier aspects
  • Even though many low-elevation locations lack snow, be mindful of avalanche runout areas at low elevations with start zones in middle elevations.
  • Avoid warming terrain traps

Thanks for submitting your observations. Snap a few photos while you’re out and send them in, it’s a huge help! Thank you.

 

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