Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Skiing and riding early in the day will work to your advantage in avoiding wet instabilities. Warming temperatures may break down the surface crust and increase the avalanche danger. Spring conditions are here. Plan your routes to avoid being under corniced ridgelines or steep sunny slopes in the afternoon.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Continued warm weather is weakening the snow surface resulting in natural and human-triggered wet avalanche activity on slopes steeper than 35 degrees. Last night's solid refreeze will delay the onset of this problem until the crust breaks down later today. In areas where a supportable crust does not exist, you can initiate a slide on the thick layer of mushy moist snow resting above a thick crust. The resulting slides may be difficult to escape due to their wet concrete-like nature. When you or your machine sink more than a few inches below the surface, it is time to move to a different aspect or elevation. If the sun makes an extended appearance, move away from these slopes to more shaded locations.

    (3/24/2022)

    Recent warm temperatures and solar input initiated slides large enough to bury, injure, or kill a person.

    Photo: Mark Dundas

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–3

    Weak layers 1-3 feet below the surface still have the potential to result in a slab avalanche. A rider's weight or snowmachine may affect these layers resulting in a slide. A cornice fall or wet loose slide could be enough mass to trigger an avalanche. Choose planar or concave slopes to maximize your chances of having a safe, uneventful day. Limit time traveling beneath steep slopes, especially as the day warms up and the surface crust breaks down. 

    (3/21/2022)

    Compression test results on a mid-elevation (5900 ft). The fracture occurred on a layer of weak snow above a crust.

    Photo: Chris Gotschalk

  • Cornices

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Prominent wind-formed features exist on many upper elevation ridgelines. These behemoths generally require sustained warming before they fail. Continued warm weather is weakening and increasing the threat of failure. Large chunks of snow may end up trundling down the slope or possibly triggering a large slab avalanche on a buried weak layer. While traveling along ridgelines, give these features a wide berth because they are notorious for breaking further back than anticipated. Limit your time spent on slopes beneath these beasts.

    (3/17/2022)

    Large seasonal cornices are found along many ridgeline locations.

    Photo: Adam Clark

Avalanche Discussion

Friday is day four of unseasonably warm temperatures, expected to continue through Sunday. This afternoon should reach 10-15 degrees above average despite mostly cloudy conditions. Fortunately, weather stations dropped below freezing between 6:00 - 9:00 Thursday night at all elevations. This should result in a more substantial refreeze of the snow surface than seen over the previous few days. 

Natural wet loose avalanche activity peaked Wednesday from a combination of warm air temperatures, strong solar input, poor overnight refreeze, and dry snow becoming wet for the first time. Thursday, I visited the Flathead Range with Megan, the FAC March intern and a GNP winter ranger. We noted about a dozen D2 Wet Loose slides on southerly aspects and around 8 D1.5 on northerlies. Most of the slides were at mid-elevations, although several originated at the upper elevations. There were fields of rollerballs in areas that did not produce slides. These findings confirmed that Wednesday's warm air temperatures were enough to affect the snow surface on slopes not receiving direct solar radiation. An observer in the southern Whitefish Range intentionally triggered two Wet Loose slides on steep easterly slopes at mid-elevations. These slides ran up to 250 feet and were D1.5 in size. 

We have dropped the avalanche danger today due to an overnight refreeze of the snow surface, forecasted mostly cloudy conditions, and decreasing natural activity; we expect minimal natural wet loose slides but anticipate that human-triggered slides remain possible. I would not trust any steep slope that is not harboring a supportable crust. 

Join us for our last education event of the season. Topics Class! The Scoop on Spring Touring, Wednesday, April 6th, 6:30 to 7:30. No registration is necessary for this in-person event.

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