Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Our snowpack remains weak and troublesome. Multiple large avalanches occurred naturally during the recent storm. Triggering a slide on a buried weak layer near the ground could ruin your season before it begins. Enjoy the soft snow on and below slopes 30 degrees or less in steepness. The danger will rise overnight into tomorrow as a new storm impacts our region.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–3

    Last week's snowfall was great for riding but increased the load onto weak layers formed in mid-November. It remains possible to trigger a slide that fails near the ground, resulting in a large, dangerous avalanche. The new snow is settling and forming a slab that can break unexpectedly wide, deep, or be triggered remotely. Collapsing of the weak layer and the resulting  whumph are indicators that you are in terrain with this weak snow structure. Choose less than 30 degrees slopes, free from overhead hazards, and build an extra margin of error into your riding lines. 

     

    (12/4/2022)

    A natural avalanche that failed on persistent weak layers. 

  • Wind Slabs

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

    Shifting winds have drifted snow onto various aspects, forming 1-3 feet thick slabs. The most recent slabs are on westerly aspects from atypical easterly winds. That will change today as winds increase in speed from the southwest. Fresh slabs may develop on leeward easterly slopes throughout the day, including mid-elevations. These wind features can be found on the lee sides of ridges, in crossroads gullies, and downwind of saddles. Look for textured surfaces or pillows of snow that feel denser or hollow sounding. Cracking at the surface and snow denser than observed in sheltered locations are signs of a slab. Triggering a surface slab may step down to a deeper buried weak layer resulting in a larger, more dangerous avalanche. Choose slopes sheltered from the wind and less than 30 degrees steep for a safer, more enjoyable experience.

Avalanche Discussion

After the recent storm, Sunday's mostly sunny conditions allowed observers to get their best view of the mountains. Most observations were from the Flathead Range and southern Glacier Park, where multiple avalanche crowns were noted. Most slides failed during the storm cycle on a layer of buried weak snow that formed mid-November. This layer is responsible for our Persistent Slab problem. 

The beat goes on…most observations Sunday noted collapsing and large rumbling whumpfing. This feedback has been nearly continuous in all reports over the past eight days, as our weak snowpack structure cannot support the weight of a rider or their snowmachine. Choosing low-angle terrain not connected to steep slopes above is the only sensible way to manage this problem. Blase was in the Swan Range yesterday and experienced widespread collapses. He wasn't worried about his party's safety because he deliberately chose slopes appropriate for the conditions. It sounds like they blissfully enjoyed the quality dry surface snow without the stress of triggering a slide on a buried weak layer. Several other experienced users followed suit and enjoyed the quality surface conditions responsibly.

A plume of moisture will enter the area Monday night and interact with a cold arctic air mass spilling over the Continental Divide. This scenario may bring heavy snow to the Flathead Range, southern Glacier Park, and especially the Swan Range. We expect the avalanche danger to rise overnight and through Tuesday. New snow avalanche problems should develop, such as storm or wind slabs. The new load will stress buried weak layers in our pack. Slides at the surface have the potential to step down to a buried weak layer resulting in a much larger, more dangerous avalanche.

Education - Our next Avalanche Awareness presentation is this  Wednesday, December 7, at Whistling Andy Distillery, Bigfork. You can get more details about this free event here. Next week, we will offer an Avalanche Awareness presentation Wednesday, December 14, at Penco Power Products, Kalispell. You can get more details about this free event here.

Check out our new Observation View page. It highlights signs of instability and allows you to filter by date or zone to pull out reports relevant to your objectives. We've updated our observation submission page as well. Try it out and help your community by sharing what you see in the backcountry. The form requires you to fill out the location fields and put a dot on a map. Be as vague or specific as you want. 

Preseason restrictions on uphill travel are in effect at Whitefish Mountain Resort.

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