Bulletin d’avalanche

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Danger d’avalanche

Sun
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Points saillants

It is likely you will find wind slabs on all aspects today at treeline and above and thin storm slabs may develop at all elevations by this afternoon as snow and rising temperatures roll through today. Avalanche danger will likely rise this evening and into Christmas day as the rain/snow line is predicted to rise to over 6,000'. For the safest riding on Saturday, stick to sheltered terrain in the timber and avoid steep slopes below wind loaded ridgelines and steep, cross loaded gullies at upper elevations.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Triggering a wind slab or thin storm slab at all elevations is possible today. Windslabs that formed under the northerly flow of the cold front will be more stubborn and resistant to triggers today, they may also be harder to see today now that we have buried them under a fresh coat of snow. Avoid open terrain steeper than 35 degrees. Loaded gullies and steep slopes below ridgeline will be the most likely areas to trigger an avalanche in the new snow. Winds have switched to their normal southwesterly pattern and will now transport snow to the north easterly aspects.

    Temperatures will rise today and snowfall densities will increase. Keep this in mind and pay attention to the surface of the snowpack. The upper snowpack will likely become cohesive and slabby as the day progresses, which will increase your chances of triggering an avalanche.

    (12/21/2022) Photo taken in Silver Valley earlier this week of an avalanche triggered in the most recent storm snow and wind loading.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    The persistent weak layer near the base of the snowpack is becoming less reactive as the weeks go by, but could still be triggered in a step-down avalanche or in areas where the snowpack is thin and void of vegatative anchors. The distribution of this layer is pretty uniform above 4,500' in elevation, but the strength and reactivity is variable, which makes it a bit of a wild card. The other persistent weakness in the snowpack would be layers of buried surface hoar, which we are still finding out there, but it has not produced any concerning results this past week.

Avalanche Discussion

It's been a dynamic week weather wise and the elements will continue to change while throwing curve balls our way. With the cold front we saw crazy temperatures and winds that kept most of the smarter people inside. Wind slabs and loading could be observed all the way down to the valley bottoms and abundant amounts of cold, dry snow. 

Next on the menu will be temperatures rising today and through the coming week, with more snow and possibly rain/freezing rain in the forecast.  Expect avalanche conditions to rise as dense, heavy snow falls atop the low density snow from this past week, creating an upside down snowpack. Monday and Tuesday appear to bring the biggest weather changes, particularly below 6,000'. The issue of concern here will be a rapid rise in temperatures while adding additional weight to the snowpack in the form of rain. Avalanche stability declines with rapid weather changes. When warm air and rain rolls in it has two effects to the snowpack. First it weakens bonds in the snow, and while doing so it also adds additional weight. Imagine holding a barbell over your head while one friend adds weight to it, meanwhile, your other friend tickles you. Eventually you are going to drop the weight in spectacular fashion. With all of the light cold snow out there I see a strong potential for "loose-wet" avalanches at lower elevations and a chance to test out the strength of our deeper weak layer.

We will be watching this potential change closely as we may see a big shift in avalanche conditions at lower elevations in the coming days.  There is still alot of uncertainty in this weather system so stay tuned!

There is still room in IPAC's Level 1 motorized avalanche class! Follow the link for details: https://www.idahopanhandleavalanche.org/friends-ipac-avalanche-safety-courses

Also, you should check out our new "Observations" platform thanks to the fund raising efforts of our Friends group and Board Member Mike Brede!

https://www.idahopanhandleavalanche.org/observations#/view

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