Avalanche forecast

Rattlesnake

West Central Montana Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Today, triggering a windslab avalanche on upper elevation east slopes is likely. On other aspects, it is possible due to shifting winds. Make careful assessments of wind features today and avoid wind loaded slopes over 35º. Loose dry avalanches are likely where the snow is not wind drifted. Take care around terrain traps where entrained sluff could push you into or over hazards. 

 

Avalanche problems

  • Wind Slabs

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

    Twelve hours of strong west winds have loaded east slopes in the Rattlesnake. Triggering a wind slab avalanche on east aspects is likely. Keep in mind that multiple aspects hold reactive windslab. Tuesday and Wednesday, easterly winds loaded west slopes. Wind slab is forming on top of crusts from last week’s rain event and facets on previously scoured faces. Wind slab is found mainly at and below ridgeline, but exposed areas midslope may be cross-loaded—exercise caution in start zones and around the loaded edges of gullies. 

    Drifted snow, cornices, wide pillows, hollow-sounding snow, and shooting cracks all indicate the presence of windslab.  As windslab sets up and gets stiffer, or if it’s very specific in its location, you may not get shooting cracks as a warning sign. A good policy is to avoid any steep start zone expected to be wind loaded.

    Today avoid wind loaded slopes over 35º. Take special care to assess wind effects on multiple aspects. 

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Up to 7” of new snow fell on Tuesday. Cold temperatures yesterday and last night have kept it soft and unconsolidated. Loose dry avalanches are likely on slopes over 38º. Due to the presence of the underlying crust from last week's rain, these were running far and fast yesterday.

    While mostly small, sluffs can create issues if encountered around terrain traps where they could push you off your feet and into or over train traps such as gullies or cliffs. Manage loose dry slides by letting them run before skiing, cutting out of sliding snow to high points, and riding ridges rather than gullies in steep terrain.

     

Avalanche Discussion

Since the last forecast, up to 7” of snow has fallen in the Rattlesnake, temperatures dipped to -5  overnight. Winds have switched from west to east and back to the west, loading multiple aspects.

Today, expect temperatures to the mid-20s. Winds are out of the west and moderate to strong. Partial cloud cover may limit solar warming. 

Sub-zero overnight temperatures and cold days have kept the new snow soft and promoted faceting. This has kept cohesive storm slab from forming. As temperatures warm over the next couple of days, we could see more cohesion in the snow and potential slabs on the rain crust. Slab formation will be accelerated on south aspects if the sun appears. 

The crust from last week's rain is still prominent and impacts skiing in most places. It’s currently proving to be a slick bed surface for loose dry avalanches. When the next round of snow, arriving Sunday, buries it deeper with a cohesive slab, we could see a widespread avalanche cycle.

Please let us know what you are finding out there. You can submit observations here.

Ski and ride safe.

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