Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sun
Alpine
4 · High
Treeline
4 · High
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Conditions are downright treacherous at mid and upper elevations. The danger will rise through the day as more snow accumulates. You can trigger surprisingly large avalanches way too easily with way too little warning. You're unlikely to survive being caught in one of these slides. Large and very large natural avalanches are likely. Stay off of, and out from under, slopes steeper than 30 degrees. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3

    8 consecutive days of triggered, remotely-triggered, and/ or natural avalanches. The slabs have grown thicker and wider as new and drifted snow have accumulated. Friday, they were breaking the full width of start zones. They are releasing on treed slopes and running at high speeds through trees. Often, however, there's no cracking or collapsing until the avalanches release. Nearly all of this activity has occurred on northwest through northeast to southeast aspects. That means you can climb a sunnier, more windward slope and get few clues to the danger, then trigger a lethal slide on the first shaded slope you encounter. The potential for natural avalanches and for triggering avalanches from nearby slopes means it's also critical to stay out from under steep slopes. Stay safe by finding fun in non-avalanche terrain.

    (2/5/2021) Natural avalanche that released mid afternoon on 2/5/21.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Sustained winds haven't accompanied this week's snowfall. But they've been gusty enough to drift snow near ridges and into the tops of chutes and on the lee sides of gullies and create some dense slabs. Expect to find these slabs in atypical locations, thanks to wind switching from the prevailing southwest to northerly. This hazard will grow more widespread as winds increse this afternoon. Debris from triggered wind slabs and falling cornices can trigger much wider and deeper avalanches as it runs downslope. Avoid being on or under steep start zones where you see blowing snow and active loading. 

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Enough low density snow has accumulated that sluffs can be dangerous on very steep slopes that are sheltered from the wind and don't harbor buried surface hoar.. This hazard poses the greatest danger at low and mid elevations, on slopes where recent snow has not consolidated into a slab above the mid-January crust. It probably exists at upper elevations too, though it's the least of your concerns if you make it to that terrain. Don't let your sluff push you into a tree well or other terrain trap. 

Avalanche Discussion

The conditions I've seen in the past two days of fieldwork are remarkably unforgiving. I expect them to get worse, with more snow forecast for today and winds spiking this afternoon. Unless you are very skilled at avoiding avalanche start zones and runouts, we recommend staying out of the backcountry.

You might think I'm overstating things if you're traveling in the northern half of our forecast region. That half of the region is just late to the party; the same structure (soft slabs over buried surface hoar and the 1/13 crust) exists on shaded slopes. However, recent snow does not seem to have consolidated into stiff slabs yet, so they're less reactive. For now. As more new and drifted snow accumulate in that part of the forecast region, expect the slabs to become more reactive and conditions to grow more dangerous. 

Southerly slopes have not produced the same kind of avalanche activity in the past week. You can find weak facets around the 1/13 crust, and tests are still producing propagation. That's enough info to keep me off of, and out from under, slopes steeper than about 35 degrees on these aspects. They will grow increasingly dangerous when winds turn to the north and start top-loading and cross-loading these usually windward slopes. 

Conditions like these are unusual in northwest Montana. Rarely do slopes remain reactive to the weight of a person or snowmachine for so long. The weather of the past week has incrementally loaded the weak snow around the 1/13 crust, steadily increasing the danger. Until the storms end, the danger will not taper off. 

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