Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
1 · Gering
Waldgrenze
1 · Gering
Unterhalb
1 · Gering
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Kernpunkte

The current snowpack is more stable than the crypto-currency market. The isolated exceptions are steep slopes with rocky start zones and convex profiles, where a person's weight can still collapse deeply buried weak layers and trigger a dangerous slide. You can minimize your risk of financial ruin by getting into the mountains. And you can minimize your exposure to the low-likelihood avalanche hazard by sticking to slopes with concave profiles - steep to less steep - and consistent snow depths.

Lawinenprobleme

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    1.5–3

    Steer clear of start zones with a convex profile and variable snow depths and minimize your time in the runouts of such start zones. These start zones are often spotted with rocks or rock bands, and positioned such that winds up or across the slope often scour away snow, leaving a snowpack that's littered with thin spots. Convex rollovers and thin spots are possible trigger points, where your weight can collapse weak layers near the ground and release destructive, too-big-to-survive avalanches. It's harder to trigger slides like these on slopes with thicker, more homeogenous snowpacks. Choose slopes that fit this description if you are going to ride in consequential terrain. 

Avalanche Discussion

You know it's benign conditions when light but variable winds seem the most notable weather of the past 24 hours. Indeed, winds did veer to the north and east late Monday, with gusts reaching into the 20s. I doubt there was much drifting and few new slabs formed; the surface snow grains on shaded aspects have faceted and are unlikely to bond into cohesive slabs. On many sunny slopes, the surface snow has melted and refrozen into a thin, unsupportable crust. Today's sun and radiation might be enough to soften these crusts on steep slopes. 

The wind slabs deposited at upper elevations last week have mostly stabilized, with few reports of instability as riders have moved into higher, more exposed terrain. That's prompted us to remove the Wind Slab avalanche problem. A few isolated slabs of drifted snow might remain reactive to the weight of a person or snowmachine in steep, rocky terrain near summits. In that terrain, remain alert for and test any drifts or slabs of drifted snow thicker than a few inches. 

This discussion would end there - and you could travel around the backcountry mostly carefree - if it weren't for a nagging concern about large to very large hard slabs breaking in old snow near the ground. On mid- and upper-elevation slopes, the season's snow rests on soft layers of weak facets or facets around hard crusts. While these basal weak layers have generally been dormant, they activated during warm storms with heavy snow earlier this month, producing several destructive natural avalanches in the Flathead and Whitefish ranges. The current spell of fair weather has brought a spike in solar radiation that could also destabilize these layers. We've had no reports that's happened so far. It's nonetheless worth reducing your exposure to this low-likelihood, high-consequences hazard. That means avoiding start zones likely to harbor these weak layers and spotted with potential trigger points. It also means minimizing your time in the runouts from such start zones. 

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