Bollettino valanghe

Whitefish Range

Flathead Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You can trigger avalanches on slopes with wind-drifted or stiffened snow. Expect to find hard, thick surface snow in unusual locations. Seek out slopes sheltered from the recent blustery conditions.

Problemi valanghivi

  • Wind Slabs

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

    Today is the third consecutive day that moderate to strong northeast winds drift snow onto atypical aspects. This loading pattern is responsible for recent large natural avalanches. Slabs may be found in unusual locations, including low elevations. These features will be the thickest and most dangerous near and below ridgelines and saddles, around prominent terrain features, and in cross-loaded gullies.

    In areas exposed to the strongest winds, slabs may be hard and supportable to you and the weight of your machine. On these slopes, the snowpack may not offer signs of instability until it is too late. These conditions are particularly concerning due to the ability of the slab to fracture above you and propagate wider than expected. Locations sheltered from the brunt of the wind may harbor softer drifts identified by dense snow that doesn't allow you or your machine to sink more than a few inches below the surface. Cracking indicates an instability directing you to a more sheltered slope or lower-angle terrain.  

    Loose Dry: Many areas exist that are sheltered from northeast winds. These locations hold substantial cold, dry snow from recent storms. Cold temperatures are slowing the rate at which this new snow settles out. Expect to trigger a Loose Dry sluff on slopes steeper than 35 degrees. Manage your sluff and limit time spent above terrain traps or in long-running gullies.

    (2/23/2023)

    Large natural avalanche on wind-loaded SE slope at upper elevations.

  • Persistent Slabs

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

    Copious recent snowfall and wind-loading have buried weak layers to a depth of several feet across the area. Earlier this week, the powerful storm initiated numerous slides on weak snow at crusts formed around Christmas and mid-January. Most of the avalanche activity associated with these layers has been on shady aspects at mid and upper elevations.

    It is becoming more difficult for the weight of a rider or their snowmachine to trigger one of these slides. This has become a low probability high, consequence situation. Digging into the snowpack is the only way to identify if a slope contains one of these weak layers. A surface avalanche has the potential to step down to a buried soft layer resulting in a sizeable dangerous slide. The easiest way to deal with this problem is through effective terrain management - avoid traveling on and below steep slopes. Steer around convexities and rocky areas where the snowpack is thin.

    (2/20/2023)

    The crown of a large avalanche on a wind-loaded upper elevation slope.

    Photo: sw

Avalanche Discussion

Arctic air will begin to moderate today and retreat to the eastside through the weekend. This morning's temperatures are frigid, but all locations should climb above zero this afternoon, with some areas reaching the teens! Impressive ambient air temperatures were recorded over the past few days, with the John F. Stevens - Marias Pass corridor the coldest—the Snowslip (7000 feet) station stayed below minus 30 Fahrenheit for 10 hours overnight Wednesday. Thursday's high was minus 24, with an additional 8 hours of minus 30 readings last night. The good news is that temperatures have climbed 17 degrees over the past few hours to a comfortable minus 15.

Moderate to strong north through east winds continue this morning before easing off and eventually being replaced by southwest winds. These atypical winds are an oddity that impacts large swaths of terrain, such as the front side of WMR, the Highway 2 corridor between Essex and Marias Pass, and the Swan front, while leaving many locations unscathed. Vast snowfields may resemble a lunar landscape in areas open to these winds. Expect to find thick, hard drifts on the leeward side of these moonscapes. 

Dangerously cold conditions have limited field observations following the bountiful storm, which impacted us earlier this week. We plan on entering the field today and continuing to catalog the avalanche activity associated with this event. So far, windshield tours have noted large slab avalanches associated with storm snow, wind-drifted snow, and buried weak layers. If you get out this weekend, please send us any photos or information regarding these slides. 

 

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