Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

The Swan Range received a potent shot of moisture overnight, creating dangerous avalanche conditions. Expect to find fresh slabs reactive to the weight of a rider in all aspects. After nearly a week of LOW danger, today is a wake-up call telling you to dial back your terrain choices and slope angles.

Problemi valanghivi

  • Storm Slabs

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

    The Swan Range received a potent shot of moisture overnight, with Noisy Basin picking up 8 inches and over an inch of water. The new snow fell on various surfaces, including loose, weak snow and crusts. The new snow depth and danger will increase with elevation, with the largest slabs downwind of ridgelines and saddles. This problem is on the surface and should be easy to identify. Look for cracking beneath your feet or machine to note a slab. Feel for a change in snow density from something light and airy to denser. Utilize hand pits to see how well the snow is bonding to the layer beneath. Choose slopes with runouts clean of surface obstacles to keep a minor incident from escalating into something worse. When in doubt, revert to lower angle slopes for a safer experience.

    (12/23/2022)

    Storm slabs developed in today's 3-4" of new snow. Skiers on a skin track triggered slabs and shooting cracks.

    Photo: Mark Dundas

  • Persistent Slabs

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

    On Friday, a rider reported a collapse on a mid-elevation slope in the southern Whitefish Range. This proves we are not out of the woods with our Persistent Slab problem. Triggering a layer near the bottom of the snowpack would likely result in an unsurvivable avalanche. Continue to choose terrain with the least likely chance of starting a slide - planar slopes free of convexities and areas with a deep uniform snowpack without exposed rocks. When in doubt, scale your slope angles back to a lesser angle.

    (12/28/2022)

    Thundering collapse at 7150 feet, east aspect, northern Swan Range.

    Photo: Cam

Avalanche Discussion

Precipitation returned to the Flathead yesterday afternoon and tapered off early this morning. The Swan Range was favored with 8 inches of new snow and 1.2 inches of SWE at Noisy Basin (6040'). Weather stations in the southern Whitefish Range and southern and central Glacier Park picked up much less, with generally 3-4 inches of snow and 0.2-0.4 inches of SWE. Unfortunately, we don't have data from the Stahl Peak SNOTEL in the northern Whitefish Range or the Flathead Range, where a wind storm made the Tunnel Ridge station inoperable earlier this season. 

The new snow fell on various surfaces, which may impact the reactivity of fresh slabs. Sunny aspects developed a thin crust this week, which extends to as high as 7500 feet in southern Glacier Park. Windward slopes above 6500 feet received a heavy coating of rime from a thick layer of clouds near the treeline or were scoured to a windboard consistency from recent blustery conditions. Slopes sheltered from sun and wind hold 3-16 inches of loose faceted snow, depending on elevation and location. Beneath the snow surface is a crust formed over the Christmas holiday that is thick and supportable at low and mid-elevations but thins with elevation. 

Following six days of LOW danger, we have increased today's danger rating due to the new snow. The snow fell at relatively mild temperatures, 28 F in Noisy Basin and 22 F at WMR, which is favorable for slab formation.  Winds overnight have generally been light, with moderate gusts. In areas with less snow, the Flathead Range, the Whitefish Range, and southern Glacier Park, we expect thin wind slab development on leeward slopes to be today's main concern. Generally, these slabs will increase in thickness and size as you gain elevation. Slabs in locations sheltered from the wind may be reactive where they sit on a crust or loose snow but should be thin and manageable. 

The Swan Range is different due to the amount of precipitation that fell in a 10-hour window. You may find fresh slabs on all aspects at mid and upper elevations with potentially dangerous avalanche conditions at upper elevations where a foot or more new snow fell. Due to the wind, slabs will be thickest on the leeward side of ridgelines and beneath saddles. Today would not be a good day to descend the steep slopes into the Picnic Lakes for those familiar with the Noisy Basin area. 

Education TONIGHT: We are pairing our final Avalanche Awareness talk of the season with 2023's first State of the Snowpack. Ted Steiner, FOFAC Board President and longtime avalanche worker, will host this fantastic evening of avalanche education. This will be held at FORLOH in Whitefish on Tuesday, January 10. TONIGHT! Get more details here.

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