Bollettino valanghe

Whitefish Range

Flathead Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Recent snowfall and wind continue forming slabs of wind-drifted snow on various slopes. You could encounter both hard and soft slabs which will be larger and more widespread as you gain elevation. Cracking in the surface snow directs you to lower-angle or sheltered terrain where the snow quality is better.  

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2.5

    You can find several generations of wind slabs on various aspects formed by this week's shifting winds. Saturday's snowfall, which favored the Whitefish and Swan Range, may become the newest addition. Slabs are soft and hard and are found in usual and unusual locations. 

    Slabs rest on weak snow formed during the January dry spell, recent low-density snowfall, or older wind slabs. This could contribute to slabs being more sensitive and propagating further than expected. Slabs become more widespread as you gain elevation and enter open terrain exposed to the wind. However, atypical winds may have left slabs in unusual locations at lower elevations. 

    Wind-drifted surfaces may resemble dunes or have a pillowed appearance. Etched surface snow (Image) indicates wind scouring. Cracking or collapsing (whumphing) are signs of a sensitive slab directing you toward lower-angle slopes.

     

    (2/7/2025) Crown of a wind slab avalanche in Path 1163 that likely ran overnight on February 5.                    Photo: Adam Clark

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2.5

    Recent snowfall rests on widespread weak snow, including surface hoar and facets, formed during the January drought. These weak layers are found in many aspects at all elevations. The surface snow has not been cohesive enough in many locations to become a problem. However, Saturday's snowfall added weight and perhaps more cohesion to the existing surface snow. Yesterday (Saturday), observers noted collapsing on their ascent and descent in Canyon Creek, an area favored by the storm.  

    As the surface consolidates into a slab, this problem will become more widespread and dangerous. Additional snowfall, wind, warming, or sun can stiffen the surface into a cohesive slab. Cracking in the snow surface or collapsing (whumpfing) are clues that you have found a sensitive slab. Due to the underlying weak layers, slabs can propagate wider than expected and be triggered from flat terrain above, below, or to the sides of steep slopes. 

Avalanche Discussion

Saturday's storm overproduced in the Swan and Whitefish Range, where 5-10 inches of low-density snow was recorded at stations.  The WMR snow report is stating that this 10 inches is the largest 24-hour snowfall of the season.  Water amounts during this storm were relatively small, with around 0.5 inches of SWE recorded. The Flathead Range and Glacier Park stations report just an inch or two of new snow.

The new snow adds weight and possibly cohesion to this week's low-density surface snow. Friday, we listed Persistent Slab as an avalanche problem in the Whitefish Range. Due to the generally soft surface conditions, a rider is unlikely to trigger a slide on a buried weak layer; however, as the surface snow consolidates into a slab, the likelihood of triggering increases. Observations suggest that buried surface hoar is more widespread in this range than in the other zones. Observers noted collapsing on southerly slopes in Canyon Creek during their ascent and descents yesterday (Observation 1, Observation 2). This may be a sign that the surface snow is becoming more cohesive.

The recent low-density snow and cold conditions have kept a cohesionless surface in many sheltered locations. On very steep slopes, riders could trigger loose snow sluffs. These can be problematic above cliff bands, in long-running gullies, or terrain traps where the snow piles up deep. Mostly cloudy conditions are expected today, but natural loose snow slides may develop on steep slopes facing the sun if the intense February sun makes a prolonged appearance.

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