Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Mon
Alpin
1 · Faible
Limite forestière
1 · Faible
Sous la limite
1 · Faible
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Points saillants

Large avalanches are unlikely. Cold temperatures have ended the recent heatwave, but small wet slides may become possible today at low and middle elevations. Slopes will be frozen this morning, but monitor the snow surface as the day warms up. If you begin sinking into wet mush, head for lower-angled terrain or a shadier slope.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    Yesterday's cold front put an end to the recent heatwave, and frigid overnight temperatures have provided a hard re-freeze of the snow surface at all elevations. As a result, wet snow avalanches will be much less likely today than they have been this past week.

    Natural wet slides are unlikely, but it may become possible to trigger small wet loose avalanches as the sun and warming temperatures thaw the snowpack surface. This will be more common at lower and middle elevation slopes—especially those that face the sun. Due to much colder temperatures up high, triggering a wet snow sluff at upper elevations is unlikely.

    Monitor how the snow surface is thawing as you travel. If you begin punching through the surface crust into wet mush below, it's time to head for a shadier slope or more gentle terrain. While upper elevation slopes may not thaw until later in the day (or maybe not at all), don't forget about the lower elevation terrain you need to travel through as you exit the mountains. 

    ADDITIONAL DISCUSSION:Persistent weak layers that formed in March led to a spate of natural and human-triggered slides at the end of the month and into early April. While the recent warming trend worsened this problem initially—leading to some warming-induced slab avalanches—over time, it helped strengthen these weak layers. Triggering a persistent slab avalanche has become very unlikely, but keep this problem in mind if your travel takes you into high elevation, northerly-facing terrain.

Avalanche Discussion

Today is our last daily Avalanche Forecast of the season. We will provide a General Information update tomorrow and an update later in the week as conditions warrant. All of the SAC staff would like to extend a huge thanks to everyone—recreationists and professionals alike—who submitted observations this winter. This information improves the accuracy of the forecast and helps all of us make better-informed decisions in the backcountry. Even though we're winding down our operations, keep these coming in and be sure to check out what others are finding on our observations page.

While the danger today is LOW across the board and the snowpack seems to be going out with a whimper, this belies the wild ride we've had over the past two weeks:

  • COVID-19. The pandemic hit Blaine County and the Wood River Valley hard, leading to a stay-at-home order and the early closure of the Sun Valley Ski Area. There has been a significant increase in backcountry traffic, especially on Galena Summit. This prompted us to write a blog post about backcountry recreation during COVID-19. We urge folks to recreate close to home and in a low-risk manner.
  • Human-Triggered Avalanches. From March 28th to April 4th, there were six human-triggered avalanches failing on persistent weak layers that formed in March. Many of these were remotely-triggered from the top or bottom of the slope, and all were large enough to bury or injure a person. This was the highest concentration of triggered avalanches we've had all season.
  • An M6.5 Earthquake. On March 31st at 5:52PM, a large earthquake struck in our Banner Summit zone during a period of HIGH danger. Incredibly widespread avalanching occurred as a result, primarily in the northern half of the forecast area but extending as far south as Ketchum.
  • An Intense Heatwave. Beginning earlier this week, we quickly transitioned from a cold, snowy pattern to the warmest temperatures of the year. Temps in the mountains soared into the 40s and 50s F, and valley bottoms hit the mid-60s F. Not unsurprisingly, this warm-up led to widespread wet snow avalanching, including some wet slabs.

So what does the future hold? Most of the forecast area is in a spring snowpack pattern where the avalanche hazard is driven primarily by daytime thawing due to warm temperatures and solar radiation. Persistent weak layers, while much improved, should remain on your radar on the highest and shadiest slopes. Late-spring storms and squalls could lead to storm slab instabilities, especially when accompanied by wind.

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