Bollettino valanghe

Banner Summit

Sawtooth 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 intense warm-up during the past few days has resulted in a number of large wet avalanches. Cooler temps today will make wet avalanches less likely, but continue to monitor snow surfaces and avoid being on or beneath steep slopes with wet, mushy snow.

Problemi valanghivi

  • Loose Wet

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

    Over the past several days, very warm daytime temperatures, intense sunshine, and weak overnight freezes have pumped a lot of water down into the snowpack on all but the highest and most north-facing slopes. These conditions have produced numerous wet snow sluffs, many of which have been large enough to bury or injure a person (photo above/right).

    This dramatic warm-up is winding down, and temperatures today will be cooler than days past. However, with a poor re-freeze at lower elevations, and sunshine in the forecast, wet loose snow avalanches will remain possible today. The best way to manage the problem is by monitoring the snow surface conditions—avoid steep slopes with wet, soggy snow or where you're beginning to punch through previously supportable crusts. Given the significant spring transition we're experiencing, it pays to be on the conservative side—don't overstay your welcome if the snow starts to become wet.

Avalanche Discussion

As the Sawtooth Avalanche Center winds down our daily Avalanche Forecasts (the last one is tomorrow), we've all had to buckle our seatbelts and hold on for a wild ride. It's been an exciting 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.
  • Human-Triggered Avalanches. From March 28th to April 4th, there were six human-triggered avalanches failing on persistent weak layers that formed in March. All of these 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 showing signs of improvement, remain a concern 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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