Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

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

The avalanche danger will gradually rise as slopes warm and weaken through the day. Triggering a large dangerous avalanche on buried weak layers remains possible on shaded aspects above 6500' that do not harbor a stout surface crust.  If you venture into this terrain, avoid slopes with a rocky or windswept look. Enormous cornices exist and should be given a wide berth on both ridgelines and slopes below.

Lawinenprobleme

  • Persistent Slabs

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

    Avalanche activity on weak layers buried 3 to 6 feet below the surface remains a concern, as evidenced by Thursday's large avalanche triggered by a cornice fall. Today is the warmest day of the week, and this incremental warming may make these layers more reactive.  You can trigger a slide where these layers are closer to the surface, such as windswept terrain or slopes with a peppered rocky appearance. Choose places with a deep, uniform snowpack instead. In areas without a supportable surface crust, stick to terrain less than 35 degrees in steepness. 

    (3/11/2021) A recent Persistent Slab avalanche possibly triggered by a cornice fall on Mt Cameahwait in the Flathead Range. Recent warming contributed to cornice failure.

  • Cornices

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

    Seasonal cornice formation is impressive across the area. While many of these behemoths have lost little of their mass, longer, warmer days with more sustained sunshine are weakening them. Friday, a skier remotely and unintentionally triggered a chunk that was 20 feet wide and 15 feet tall. A natural cornice fall resulted in a large avalanche Thursday in John F. Stevens Canyon. Today's warm temperatures and sunshine will continue to weaken these wind formations.  While traveling on ridgelines, stay well back from the edge, which is generally further back than you realize. Don't dawdle on slopes beneath these features.

    (3/5/2021) The large Rubideau cornice in the Apgar Range in GNP. This cornice develops from west-southwesterly winds and did not fail during the recent warm-up.

Avalanche Discussion

The depressing brown valley floor may temper your enthusiasm for riding, but conditions are actually quite good. Well, good as far as the 2020-21 season goes. Despite spring being one week away, we have enjoyed spring riding conditions on sunny aspects where a strong supportable crust has allowed for easy traveling. On steep slopes, this crust extends to 7000 feet or higher and is several inches thick. Observations have been few and far between lately, but FAC staff has found several inches of dry snow on shaded slopes above 5500 feet in the Flathead Range, allowing for fun powder riding. This area did not receive the brunt of the freezing rain crust, putting a damper on conditions in the Swan and the Whitefish Ranges a week or so ago.

This week's weather has been nearly perfect for corn conditions. Cold clear nights followed by sunny but cool days have kept the surface frozen in the morning and softening for just a few hours each day. The boot top to knee-deep mank of last week is a thing of the past, for now anyway. Expect more of the same today, although temperatures were several degrees warmer overnight and should rise several degrees above yesterday's high readings. 

Today's warm temperatures will allow for spring-time avalanche activity to increase. Fortunately, the wet loose hazard is mostly over due to slopes being worked over by the sun since last week. Expect to trigger small wet loose slides on very steep terrain after the slope softens like Cam and his group experienced Friday in southern Glacier Park. The large whale-sized cornices below ridgelines are weakening due to the sun and warm temperatures. A large cornice was remotely triggered Friday unintentionally in John F. Stevens Canyon. Fortunately, the skier was savvy enough to travel well behind where he thought the ground's edge was and where the cornice began. This large chunk of snow did not trigger a slide on the slope below, but Thursday, a large Persistent Slab avalanche initiated from a cornice that failed naturally. The Persistent Slab avalanche problem may become more reactive with warm temperatures as evidenced by a recent slide reported Friday. Lastly, large glide cracks can be found in all zones of our forecast area. The brown frown is generally a spring phenomenon where the entire snowpack creeps downhill. Fortunately, our recent string of cold clear nights and modest daytime high temperatures keep these mostly in check. A glide crack that either failed or crept downhill was spotted by the Patrol Fund Level 1 class in the southern Whitefish Range Thursday. 

Clancy utilized his acting talents in this week's weekly update video which we recommend you watch. It is found in the media gallery or here.

 

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