Boletín de aludes

Swan Range

Flathead Avalanche Center
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Peligro de aludes

Wed
Alta montaña
4 · Fuerte
Límite del bosque
4 · Fuerte
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

The avalanche warning has been extended for the Swan Range, the Flathead Range, and Glacier National Park. Very dangerous avalanche conditions developed overnight with heavy snowfall and strong wind. Natural and accidentally-triggered avalanches occurred yesterday and are likely today. Avalanches failing in the new snow can step down to buried weak layers resulting in a much larger, deadly avalanche. Avoid traveling in or under avalanche terrain.

Problemas de aludes

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    A snotel weather station in central Glacier Park reports 2.6 inches of Snow Water Equivalent (SWE) in the past 48 hours. Stations in the Middle Fork and John F. Stevens Canyon report a foot of new snow with over one inch of water on the valley floor. Noisy Basin in the Swan Range has picked up 1.3 inches of SWE overnight. Add warm temperatures and windy conditions to the mix, and we have a developing storm slab problem. Expect slabs to increase in thickness with elevation. They'll be considerably thicker in drifted areas such as downwind of ridgelines, or in cross-loaded gulleys. An avalanche in the surface snow can step down to a buried weak layer resulting in a large dangerous avalanche.  Stick to lower angle terrain and stay away from slopes steeper than 30 degrees.

    (2/19/2021) Rider intentionally triggered slabs 1 to 2 feet thick on convex rollovers.

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    2–3

    Buried weak layers one to four feet beneath the surface are responsible for an impressive string of accidentally and remotely triggered slides over the past several weeks. New snow and wind are adding stress to these layers, and we assume there was a natural avalanche cycle overnight. Today, the potential for human-triggered slides has increased and these weak layers are at their tipping point. Dealing with this problem today is simple - stay off, and away from avalanche terrain. This includes low-angle slopes underneath, or connected to avalanche terrain, including runouts in the valley floor. Any terrain 30 degrees or steeper is suspect today. If you are not confident in identifying these slopes, you should not recreate in the backcountry today.

Avalanche Discussion

The National Weather Service forecasted an Atmospheric River to impact our area Monday into Tuesday morning. This large storm prompted us to issue an AVALANCHE WARNING for all zones yesterday morning, even though the bulk of the moisture was arriving later in the day and overnight.

The storm took its time to arrive, but it has delivered well over an inch of water to the Swan Range, the Flathead Range, southern Glacier Park, and interior Glacier Park. The northern Whitefish Range was left nearly high and dry while the southern Whitefish Range picked up a respectable 6-8”. We have extended the AVALANCHE WARNING through tomorrow morning for all zones except the Whitefish.

We recommend that you avoid all avalanche terrain today. That includes slopes underneath, or connected to avalanche terrain. If you can not identify these slopes, this is a day for you to avoid the backcountry.

FAC staff has been following the development of this storm for several days. It’s not that we were drooling over a big powder day. Instead hoping for a heavy load to initiate a widespread avalanche cycle on our buried weak layers. We were hoping the steep slopes harboring buried weak layers would flush into the valley floor and relieve us of some of the anxiety we have with our Persistent Slab problem. Time will tell how much damage this storm system does. If you get out in the coming days and come across debris or note crowns, please fill us in on what you see. Observations from the public have been outstanding this season, and we ask for you to keep those obs heading our way.

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