Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Above-freezing overnight temperatures and rain up to 7,000' bring wet snow avalanches to the table again today. The likelihood of encountering one of these slides will increase when the crust on the surface of the snowpack breaks down. Monitor the surface of the snow you are traveling in and find somewhere else to ski or ride if it is becoming wet and unsupportable.

Avalanche problems

  • Loose Wet

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

    Overnight temperatures hovered near or above freezing for the 4th night in a row. Clear skies allowed for the surface of the snowpack to freeze but underneath this crust you will find a warm, wet, transitional snowpack. We may see brief periods of sunshine this morning before clouds build with the incoming cold front. With similar surface conditions yesterday, it only took an hour or two for the sun to melt the crust on the snow surface. Buiding clouds today will limit incoming solar radiation but may bring rain showers up to 7,000'. As the sun and rain break down the surface crust the likelihood of encountering wet snow avalanches will increase. 

    Yesterday, I observed a large skier-triggered avalanche that occurred on Senate Peak in the Boulder Mountains, near Galena Lodge (photo at right/above). Based on other observations, the slide likely occurred around noon. Based on its appearance and timing, the slide occurred after the surficial crust had been melted which allowed it to gouge down through wet snow and run near the ground. I didn't get a good view of the debris but based on the amount of snow that it entrained I wouldn't be surprised if the slide was large enough to bury a person. Either way, being drug downslope through rocks and trees in this type of slide would be an unpleasant experience.

    ADDITIONAL DISCUSSION: WET SLABSWet slab avalanches are unpredictable beasts. These slides occur when melt-water in the snowpack pools on a layer in the snowpack and weakens the bonds there. The conditions that produce these types of slides are much more predictable than the avalanches themselves. We are most likely to see wet slab activity during extended periods of above-freezing temperatures. Hmmm, that sounds familiar. Unfortunately, spring doesn't always lead to a predictably stable snowpack (watch Chris's video from Galena Summit on Friday). Rain falling up to around 7,000' this morning will add some extra water to the system, increasing the likelihood of these slides. Hanging out under steep slopes that are getting rained on is not a good idea today.

    (4/4/2021) Senate Peak, S/SW aspect, 10,100'.

Avalanche Discussion

We are at the end of the warmest temperatures of the year thus far and the snowpack has not had a solid freeze for 4 days. We have a scientific term for this: our snowpack is a hot mess. Rain falling up to 7,000' this morning is only going to make things worse. As I write the forecast this morning and think about where I'll go skiing today, I find wet snow problems at the front of my mind. Yesterday's human-triggered avalanche on Senate Peak that gouged to near the ground is a great illustration of the type of wet snow avalanches that our saturated snowpack is capable of producing. However, it isn't the only type of wet snow problem we are faced with. There are several layers in our snowpack that could make good candidates for failure planes in wet slab avalanches. In the middle of the snowpack, we have a layer of crusts, facets, and buried surface hoar that produced significant avalanche activity during the month of February. Further down, near the base of the snowpack, is a layer of large-grained depth hoar that produced widespread avalanche activity during the months of December, January, and February. Both of these layers went into a state of dormancy but may be prime candidates for producing wet slab avalanches.

When we think about wet loose avalanches we are generally thinking about a pattern of activity that varies each day. As the day heats up the surface of the snow softens and gets wet and these avalanches become possible. At night, cooler temperatures allow the surface to freeze and the likelihood of these slides decreases significantly. Picture this pattern as a wave that crests every day, reaching a maximum in the afternoon and a minimum overnight. The pattern of wet slab hazard is more complex. During the past four days, the likelihood of these slides has slowly crept up as temperatures warmed and only weak freezes occurred at night. The sprinkles of rain this morning may be the straw that breaks the camels back, or they may not do much at all. My educated guess is that the snowpack will be able to handle some light rain, but my confidence in that prediction is low. I can tell you this with certainty: you won't find me hanging out in or under steep terrain that is getting rained on today.

Even though wet snow problems are at the forefront of my mind, I'm keenly aware that today's storm may bring the possibility of dry snow problems at upper elevations. Forecasted snowfall amounts are expected to be light, which will limit the extent of this type of problem. However, by the end of the day triggering one of these slides is a real possibility at upper elevations. If you're traveling in this terrain and finding fresh snow and wind slabs be alert to the consequences of being caught and carried in the terrain that you are traveling in. And, remember that you will have to travel through a warm, wet, unconsolidated snowpack at the end of the day to get back to your car. 

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