Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Fri
Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Highlights

Warming temperatures and forecasted sunshine may initiate small, wet loose slides in the surface snow. If you notice moist snow or rollerballs developing, move to a shaded aspect and drier conditions. In isolated locations, you may encounter thin slabs of wind-drifted snow. Cracking in the snow surface indicates you have found an unstable pocket of snow.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–1.5

    In isolated locations, the wind has blown strong enough to drift snow and form thin slabs, which may be reactive to the weight of a rider.  These features are found beneath upper-elevation ridgelines, saddles, or cross-loaded gullies. They may also be encountered in favored windy locations at mid-elevations. Look for a textured surface, blowing snow, and dune-shaped features to confirm the wind has been at work. If you find cracking beneath your feet or machine, move to a more sheltered location.

    Blowing snow like this indicates that the wind is drifting snow and possibly forming wind slabs beneath the ridge line. 

    Photo: Rob Millspaugh

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–1.5

    Increasing air temperatures at mid and upper elevations yesterday and overnight are warming the cold surface snow for the first time. Today's forecasted sunshine could initiate wet loose slides in this weak, faceted snow. Slides should remain small due to just a few inches of surface snow available. The exception will be in long-running gullies, large steep continuous terrain, or where the snow breaks through the underlying crust and entrains more snow. If slides occur, they may travel further than expected due to the underlying crust. If the surface snow becomes moist, move to a shaded aspect harboring dry snow to avoid this problem. 

    Well-developed rollerballs were noted on mid-elevation slopes. These are a precursor to wet slides.

    Photo: Mark Dundas

Avalanche Discussion

Wednesday, a warm air mass on the east side of Glacier resulted in St Mary topping out at a balmy 54F. Warm upper-elevation air moved west over the Continental Divide with temperatures climbing above freezing at ridgetop locations in southern Glacier Park and the Flathead Range, with Tunnel Ridge wind (6796 feet) reaching 39F. In the Swan Range, upper elevations also warmed, with Aeneas Ridge (7186 feet) at freezing. The Whitefish Range escaped the warm air intrusion, with mid and upper-elevation stations remaining below freezing. Below the inversion, temperatures remained cool.

Warm conditions spread overnight to the previously cool mid-elevation band and the Whitefish Range. As of 0400, the Tunnel snow station  (5895 feet) is at 33F, 10-12 degrees warmer than yesterday afternoon, while Hornet (6500 feet) is at 31F. These temperatures are the warmest the surface snow has experienced since it fell five days ago.  The combination of this morning's temperatures and forecasted sunshine may initiate wet loose slides on sunny aspects. 

During the December 23 snowfall, the wind speeds were unusually light, with observations noting minimal evidence of wind transport over the past few days. Yesterday (Wednesday), Rob and blase visited Noisy and Jewel Basin in the Swan. They noted wind-transported snow, while the Aeneas Ridge weather station recorded speeds capable of transporting snow (>16 mph) since 11 a.m. Wednesday. An observer in the northern Whitefish Range found a reactive older wind slab on a northerly upper-elevation slope. The group was so concerned that they backed off a steep, larger objective.

Generally, dry loose avalanches are not a concern 2-3 days after a snowfall. However, recent cold, clear nights have allowed the surface snow to facet, weaken, and not settle as fast as usual, as noted by the USGS crew in the Swan Range. A seasoned backcountry traveler triggered dry loose slides on steep northerly aspects in the Whitefish Range Wednesday. These sluffs are becoming more stubborn to trigger, and the resulting slides are smaller than a few days ago. The consequences of a small sluff can be magnified in a long-running gully or on a slope ending in a terrain trap.

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