Bollettino valanghe

Bollettino valanghe

Payette Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

The avalanche hazard is Moderate today.   Very warm temperatures are forecasted through tomorrow with no overnight refreezing of the snowpack.  Wet loose avalanche activity will increase as the day warms starting with East facing slopes and moving around the compass through this afternoon.  Multiple weak layers and crusts existed in the upper two to three feet of the snowpack prior to the warm-up this week and are now saturated by the melting snow above.   The potential for larger wet loose avalanches,  widespread cornice failures, and naturally occurring wet slab avalanches will increase through the day as temperatures warm.  Avoid traveling in or below steep terrain as the snowpack continues to weaken today and over the next few days.

 

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Certain
    Dimensione
    1–1.5

    Today will likely be the warmest day of the year so far.  Our low temperature overnight at the Granite Weather Station(7600ft) was 39 degrees.  These temperatures are not allowing the snowpack to refreeze at night and are weakening the snowpack more each day.  You can expect to see wet loose activity beginning as the sun warms East slopes this morning with an increase by mid-afternoon.  Wet loose avalanches often begin as small point releases and can easily grow in size as they travel and grab more wet snow in their path.   Pay attention to the terrain you are near as temperatures warm and avoid steep slopes and terrain traps like gullies and avalanche paths.  

    The avalanche in the photo on the East Face of North Bruin likely occurred on Wednesday and ran just over 2000 verticle feet.  We can expect to see more wet loose avalanches of all sizes today.

    N. Bruin Mt. East aspect.

  • Wet Slabs

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

    With a rapidly warming snowpack, meltwater begins to seep down through the snowpack.  As we transition away from a cold snowpack and the persistent weak layers that we have been talking about over the last few weeks get saturated by this meltwater, there is a growing potential for natural wet slab avalanches on the weak layers or the crusts that are now buried between 1 and 3 feet deep in the snowpack.  Wet slab avalanches are like big, rogue waves.  They are unpredictable and relatively rare until conditions line up.  All of the conditions are lining up with the weak layers in the snowpack and another day of very warm temperatures.  Sunday is forecasted to be the warmest day of the year which will add to the problem.  Overnight temperatures are not predicted to start cooling off until early next week and the snowpack will take several days to refreeze once temps start to drop.  Wet slabs require a healthy dose of respect as they can be very destructive and unsurvivable if you were unlucky enough to be the trigger or get caught below one when it started.  They are also very hard to predict.  Avoiding steep terrain and giving the snowpack a chance to heal after this heatwave are your best choices right now.

    Wednesday we observed wet or saturated snow down at least 60 cms(24 inches) in the snowpack.  Both of the crust/weak layers were allowing water to pool above them creating the perfect lubrication for a wet slab above (see photo). 

Avalanche Discussion

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Today marks the 4th day in a row of little to no overnight freeze and very warm daytime temperatures. Wet loose avalanches and sloppy snow have been the theme so far.  Wet loose avalanches are typically fairly predictable and manageable and involve mostly just the surface of the snowpack. As the day gets warmer and the snow becomes more saturated, the hazard of wet loose avalanches rises and can involve more of the snowpack   Wet slab avalanches are another type of wet snow avalanche and are different beasts than wet loose.  They are much more difficult to predict and can be much larger and more destructive than loose avalanches.  Cornice failure is another side effect of a rapid warm-up,  I don't travel under cornices during warm weather at all.

Our snowpack has several key ingredients that should make you wary of the possibility of wet slab avalanches over the next few day or until we see a significant refreeze in the snowpack.

  1. Persistent weak layers buried within the upper 2-3 feet of the snowpack before the snowpack started to melt.
  2. A variety of different crusts in the upper snowpack
  3. Abnormally warm temperatures that are flooding the snowpack with meltwater which is allowing the snowpack and the weak layers to become saturated and lubricating crusts.
  4. Failing cornices- there are some large cornices that will be failing with the heat and bombing slopes below with tons of weight.

As the temps soar this weekend, we need to be thinking of changing avalanche hazards and the possibility of abnormal avalanche conditions.