Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
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

Be wary of fresh wind loading on atypical aspects and in unusual locations. Older generations of wind slabs still lurk in cross-loaded slopes and along ridgelines. You will find the best riding in terrain where the snow is soft and sheltered from the wind.

Problemi valanghivi

  • Wind Slabs

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

    Yesterday northeast winds drifted new snow into thin slabs on southerly and westerly aspects, the opposite of where you usually find them. These atypical thin slabs will likely be in upper elevations. A week of strong southwest winds drifted snow into thicker slabs on NW to SE leeward slopes near ridgelines, and cross-loaded terrain features further downslope. This older generation of wind slabs appears stubborn; however, don’t be lulled into trusting older slabs. In steep terrain, avoid riding on pillows of dense, thicker snow. Thin slabs may appear to be small, but there are slabs capable and thick enough to drag you into a tree or push you over rocks. You can avoid the problem by choosing terrain where the snow is sheltered or being scoured by the wind.

    (2/13/2023) Moderate to strong westerly winds cross-loading the south face of Running Rabbit Mtn. Photo: Adam Clark

  • Persistent Slabs

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

    Weak layers of buried surface hoar and facets exist 1 to 2 feet below the surface in the Flathead Range and Glacier National Park. You can avoid this problem entirely by sticking to slopes with lower slope angles. If you decide to step out onto steeper slopes, avoid convex rollovers where you are more likely to trigger a slide. Even small avalanches have the potential to step down to buried weak layers. Choosing slopes with runouts free of trees and cliffs is a way to reduce your chances of trauma if the unexpected happens. Conservative terrain choices and a wide margin of error is the way to manage this problem.

    (2/8/2023)

    Poor upper snowpack at middle elevations in the Flathead Range. 

    Photo: Cam

Avalanche Discussion

Tuesday’s Valentine's Day snowfall added a meager one to two inches of new snow, along with cold northerly winds that dropped temperatures. Most weather stations reported a drop of 10 degrees or more when the winds shifted from southwest to northeast around midnight. 

The added windchill made for below-zero temperatures across our forecast zones. Northeast winds were mostly light, but these shifting winds deposited small fresh wind slabs. Although the past few anticipated snow storms have underproduced, wind-loaded slopes remain our primary avalanche hazard. Both of my recent visits to avalanche sites have been steep cross-loaded slopes on northern aspects. Backcountry travel in many of our areas will continue to include snow surfaces that are heavily wind-affected.

Yesterday’s mostly clear skies and good visibility set the stage for observers to get into the backcountry. They reported isolated cracking in drifted snow and views of well-developed cornices. Our recent weather and trends in the snowpack include natural and human-triggered avalanches within the past week. If you are out riding today, continue to monitor changes in snow depth, snow density, surface cracking, and be sure to pay attention to what is above you. Human-triggered cornice failures have been reported in southern Glacier National Park.

Today, temperatures are forecasted to stay below freezing, but in the event that the sun does make an extended appearance, keep an eye out for roller balls as the surface snow warms and move to shaded slopes. Rollerballs are a sign of an impending wet loose avalanche problem. It is best practice to turn to shady aspects or to get off of steep south-facing slopes if you begin to see this happen.

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