Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

After the recent stable weather, the avalanche danger has trended down. Stay alert for snow drifted into slabs near ridgelines at upper elevations. Whumpfing collapses and shooting cracks are reminders that we still have a persistent weak layer lurking in our snowpack. To reduce your chances of triggering avalanches that break on this deeply buried weakness, stick to slopes less than 35 degrees.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Think twice before committing to steep terrain likely to harbor slabs of drifted snow. This terrain includes the lee sides of ridges, which are often marked by cornices. It also includes the tops of chutes, cross-loaded gullies, and steep slopes downwind of saddles and passes. Some hard slabs created during the Christmas storm cycle may remain unstable. Some small, soft slabs may exist as well, formed by wind gusts Thursday and today. These hazards are isolated at mid-elevations.

    Dig below the surface snow to check for older hard slabs. They tend to break above you, so slope cuts can be a deceptive and dangerous test for that hazard. Slope cuts are more predictable and safer for soft, freshly formed slabs. Cracking in wind-blown snow is a clear sign this hazard is present.

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    We can’t write off the potential for triggering large avalanches that break on weak, faceted snow buried in November. Cam reported loud collapses and shooting cracks on the east side of the Swan Range Wednesday. Other evidence – lack of propagation in tests, lack of whumpfs - suggests the problem is becoming less reactive and more isolated.

    Avoid slopes where you’re most likely to get surprised and where surprises would have the most consequences. That profile includes slopes with one or more of the following characteristics: steeper than about 35 degrees, above terrain traps like trees, gullies, and alder thickets, and littered with possible trigger points like convex rollovers shallow patches of snow due to sun or wind scouring.

    (12/28/2022)

    Thundering collapse at 7150 feet, east aspect, northern Swan Range.

    Photo: Cam

Avalanche Discussion

In honor of National Bacon Day (today) and helping you plan for some fun by getting out in the backcountry this weekend, we’d like to highlight our new observation submission page. One feature to point out is the view page that filters observations by zone or date, and also color-codes instabilities observed with red, orange, and blue dots. The red dots code for avalanches observed. The orange dots code for observed collapsing and cracking. And lastly, the blue dots are observations that report no signs of observed instabilities. A quick glance shows more red and orange dots than blue dots.

Low clouds and obscured skies have limited our observations of the recent natural avalanche cycle that occurred earlier in the week. It's looking like the Christmas storms produced widespread avalanches. Mark was able to get out on Thursday in the Flathead Range and observed that numerous dry soft slab avalanches occurred early in the storm and were mostly D2-2.5, with one or two D3-sized avalanches. These slides ran far and wide with debris covering runout zones. As the atmospheric river continued, the following cycle of slides consisted of large D3, destructive wet loose avalanches. Another professional observer reported additional evidence of the same cycle further south in the Flathead Range. He noted numerous slides including several large D3 wet loose.

One classification scheme used to determine avalanche size is Destructive Force. This is based on a scale that varies from 1 to 5. We estimate the destructive potential of the avalanche from the mass of deposited snow and assign a number. The avalanches which we normally see include:

D1 - relatively harmless to people

D2 - Could bury, injure, or kill a person

D3 - Could bury or destroy a car, damage a truck, destroy a wood frame house, or break a few trees.

With the number of D2 and D3 slides reported, travel in the backcountry last week would have been dangerous.

The general trend of avalanche danger is decreasing with seasonal temperatures and limited precipitation. We’ve dropped the Storm Slab problem today, as this problem tends to stabilize within hours or days following a storm event. The Wind Slab problem is also generally decreasing due to light winds throughout our forecast area. The Persistent Slab problem is still with us, as Cam observed on Wednesday. However, we’ve observed that it is generally less reactive and increasingly more difficult to trigger.

Training: Now's a great time to hone your companion rescue skills. Transceiver parks are open at Whitefish Mountain Resort, one at the summit and one adjacent to Grey Wolf. Both are accessible to snowmachines. You can get more details about training and education opportunities events on our events calendar.

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