Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

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

Recent snow and cooler temperatures have improved skiing and riding conditions. In terrain exposed to the wind, thin drifts reactive to a person's weight may be found in unusual locations. Triggering a large destructive avalanche on buried weak layers remains a decreasing possibility of high consequence.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Increasing northeast winds throughout the day will drift recent snow and may form thin slabs on atypical aspects. Expect to find these features downwind of ridgelines, saddles, or on the sidewalls of cross-loaded gullies. As you gain elevation, slabs may increase in thickness and become more widespread. These may form on crusts, which makes them easier to trigger.

    Fresh cornices, dunes, rippled snow surfaces, and areas with stiffer snow are telltale signs of wind transport. Cracking beneath your boards or machine is a sign of an unstable slab. 

    (3/9/2024)

    Wind drifting that causes sculpted snow dunes, as shown in this photo, are identifying signs of wind transport.

    Photo: Flathead Avalanche Center

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    Triggering a large avalanche failing on buried weak layers 2-4 feet below the surface is trending towards unlikely.  You can reduce your risk by avoiding steep, rocky, heavily wind-affected terrain on shady slopes, where the weak layers have been best preserved. In some locations, southeast aspects also contain a mix of crusts and faceted layers, so be aware of where you travel, especially in upper elevations.

    Avalanches caused by persistent weak layers release in surprising ways. Before triggering an avalanche, you may not experience snowpack collapsing or other obvious signs of instability. Choosing lower-angle terrain without convexities is the easiest way to manage this problem.

    (3/17/2024)

    This is a hard slab avalanche on Nyack Mountain that failed on a northeast aspect at upper elevations on March 16. This slide likely failed on a layer of facets above the early February crust.

    Photo: Mark Dundas

Avalanche Discussion

Today, another round of light snowfall is forecasted as a Pacific cold front enters our region. Accumulations of several inches of new snow should not raise the avalanche danger. However, there may be a slight uptick in the avalanche hazard, as a cold Canadian air mass brings a greater chance of snow overnight, with a steep drop in temperatures.

Two teams of FAC staff were out yesterday. Mark and Jeff traveled to southern Glacier National Park, where they found several inches of fresh low-density snow with little wind effect. The recent heat wave left a thick, supportable crust on sunny slopes but only a thin crust on shaded slopes. An upper-elevation snowpit on a northerly aspect showed a strengthening snowpack.

In the southern Whitefish Range, my partner and I managed sloughing in the morning and skied heavy sun-cooked snow by the afternoon. Other observers in the area reported northerly aspects staying dry, which will likely be the slopes holding more winter-like conditions. 

A mixture of unsettled weather will continue through early next week. If you spend your spring break catching up on riding and skiing, please submit an observation to let us know what you see. 

Help avalanche researchers! The Colorado Avalanche Information Center, the Avalanche Research Program at Simon Fraser University, and the U.S. National Science Foundation National Center for Atmospheric Research are researching how skiers, snowmobilers, snowshoers, ice climbers, and anyone else who travels in the backcountry interpret avalanche forecast information. This research includes a survey to understand better how helpful avalanche forecast information is for trip planning. 

Completing this survey will take approximately 20 minutes. Thank you!

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