Bollettino valanghe

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Incoming weather will bring cold temperatures, modest snowfall and moderate southwesterly winds begining Saturday night. This weather will cause windslabs to build and become more reactive in steep and exposed terrain on Sunday. Although the snowpack has been slowly trending toward greater stability, a fragile and faceted layer remains buried 1’ to 3’ deep. The potential to trigger a large slab remains possible. Do not become complacent: continue to make good terrain choices and practice safe riding habits.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Although it’s showing less reactivity, trigging a large avalanche on a buried layer of weak November snow remains possible. Kevin Davis summed it up well in Tuesday’s Selkirk/Cabinet forecast, “What we're dealing with is a structural problem. We have built our house on a foundation of potato chips.” The layer is widespread, 1’-3’ft deep, and difficult to predict. It is most likely to break in steep (>35°), unanchored terrain and could be triggered remotely from above, below or adjacent slopes. The layer of surface hoar buried under our last shot of storm snow is not proving to be reactive in stability tests but should be on your radar in steep and sheltered openings near treeline. See photo of Willow Peak taken earlier in the week.

    The challenge right now is to not become complacent. Pay attention to slope angle, travel one at a time with eyes on your partner, heed whumpfs and shooting cracks and avoid terrain traps. Choose low angle and sheltered terrain for the safest riding today.

  • Wind Slabs

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

    Wardner Peak weather station was recording winds last night out of the south-southwest at moderate speeds. With an abundance of light snow to blow around and more predicted to fall Saturday night through Sunday, it will be time to be alert to the potential for windslabs building below ridgelines. As the weekend progresses be alert to changes in density under foot and watch for shooting cracks, these are sure signs that the wind is transporting and packing the snow into a cohesive slab.

Avalanche Discussion

The skiing/riding conditions remain great with lots of soft powder in sheltered terrain. The difficulty right now is not letting a lack of feedback give you false confidence about the strength of the snowpack.

Our season total snow depth remains shallow (100-150cm), which means the buried persistent weak layer is never far from the surface and could be triggered by a skier/rider if they hit just the right spot. Thursday we performed two extended column tests in the same pit: One sheered on 29 taps (ECTP29) 31inches (80cm) from the surface. The second, a couple feet away, did not propagate. The only difference was that the first column had a rock and cavity buried in the snow right behind it, illustrating that the weak point in the snowpack is nearly impossible to pinpoint, but could be anywhere. Pit observations from Silver Mountain Patrol revealed propagation on a layer of surface hoar 20 cm above the ground (ECTP 26).

For an insightful explanation of the current conundrum that is our “deceptive” snowpack I recommend reading Blase Reardon’s, Executive Director of Flathead Avalanche Center, Forecast Discussion from yesterday, Thursday Dec. 15th (https://flatheadavalanche.org/avalanche-forecast#/whitefish-range), before deciding to huck into big terrain.

Looking ahead: conditions look like they will remain stable through most of Saturday. Saturday afternoon into Sunday an arctic blast will begin to move into our area from the east, with the potential for frigid temps and significant snow. Remember snowpack likes the weather to be boring: mild temps and little helpings of snow. Dramatic changes in weather are times that avalanche danger increases. Note that forecasts show the winds carrying the arctic blast will be out of the north and northeast, opposite our typical weather pattern, so wind slabs may build in unusual locations.

Call to action: Avalanche professionals rely on weather reports, snotel sites and field days to gather the data needed to build a forecast. But effective avalanche forecasting is a community effort: please submit observations. Don’t be intimidated, you don’t have to be a professional to make observations. Basic information such as: location, snow depth, whumpfs, shooting cracks, wind effected snow, and incidents of natural or human triggered avalanches are all helpful in building a more complete picture of what is happening across the forecast area. Help us help you. So far this season there have been five observations submitted to IPAC by the public. I hope you all have made more than five trips into the backcountry! Thanks for submitting.

There is still room to sign up for a Level 1 avalanche class designed  for the Motorized crowd! Click the link below to learn more:

https://www.idahopanhandleavalanche.org/friends-ipac-avalanche-safety-courses

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