Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
1 · Debole
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In sintesi

Natural and human-triggered avalanches occurred across the area Saturday. Warm and windy conditions have formed a surface slab reactive to the weight of a rider or their snowmachine. Today's new snow and wind will add to the problem. Dial back your expectations and choose terrain less than 35 degrees in steepness that is free of convexities or rollovers. Areas sheltered from the wind will offer a safer experience. 

Problemi valanghivi

  • Wind Slabs

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

    Wind speeds increased Friday night and have remained at a level capable of transporting snow. Saturday, observers reported "gale force" conditions with wind stations reporting gusts to 70 mph at Aeneas Ridge and 53 mph at Tunnel Ridge. An extended warming period began overnight Friday and has transformed the loose, low-density surface snow into a more cohesive layer. Natural and human-triggered slides occurred Saturday on steep slopes at mid and upper elevations. Some of these slides ran far and fast on the underlying crust. Yesterday's observations contain numerous red flags which should influence your terrain choices today. Choose slopes less than 35 degrees in steepness, free of convexities, with clean runouts. Terrain not affected by the wind will be your safest bet.

    (3/12/2022)

    An observer saw numerous skier triggered avalanches in the Flathead Range. All were small (D1) in size. 

    Photo: Andrea Goodrich

Avalanche Discussion

Saturday was an active day for natural and human-triggered avalanche activity, with slides reported in all three zones. The surface snow has changed since Thursday and here is a brief summary of why this occurred. Cold low-density powder fell early in the week, and arctic air kept the surface cool and cohesionless. Warmer air from the southwest arrived overnight Friday and stiffened the surface snow on all aspects. Southwest winds increased overnight Friday and transported substantial snow onto leeward slopes. The relatively warm temperatures and breezy conditions continued overnight Saturday into Sunday morning. Fresh snow entering the area today will add to the problem.

The number of natural and triggered slides Saturday surprised me. Widespread reactive slabs seem relatively uncommon in northwest Montana, outside of heavy snow events or loading on a touchy layer of well-preserved buried surface hoar. It appears that the stars aligned with warming temperatures and wind loading onto a layer of near-surface facets. More slides were reported at mid-elevations than at upper elevations. Perhaps this is partly due to the formation of near-surface facets being more widespread or better preserved at that elevation. Regardless, this is the reason we are giving similar danger ratings to both the mid and upper-elevation bands. We have bumped the danger up due to our uncertainty with how long freshly formed slabs will remain reactive. We will take a closer look at the problem today and readjust our ratings for Monday.

Most of yesterday's activity was reported from the Flathead Range (Observation 1, Observation 2, Observation 3), with one each from the Swan Range and the northern Whitefish.

The Friends of The Flathead Avalanche Center and FVCC are hosting the last Intro to Avalanches next weekend. And on March 22, join us online for a Community Chat where we review recent conditions and debrief a near miss.

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