Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Frigid temperatures combined with wind chill are creating dangerously cold temperatures. Moderate to strong east winds are blowing throughout most of the forecast area. If you venture out today, avoid wind-loaded slopes over 35º where it is possible to trigger wind slab avalanches. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–2

    Windslab in the Bitterroot is tricky today as winds vary dramatically from the north to the south. 

    Lolo Pass has had 24 hours of strong to extreme east winds, and windslab will be found at lower elevations. West slopes are loaded and cross loading will be an issue, with windslab found on multiple aspects.

    The southern Bitterroot has had mild northerly winds, limiting snow transport. However, strong west winds over the weekend loaded east aspects with touchy windslab. It may still be possible to trigger these. 

    The central Bitterroot lacks wind sensors, so it’s unclear what the winds have been doing in this area. Depending on where you are touring, some combination of windslab on east and west aspects can be expected. 

    It will require careful slope evaluation throughout the Bitterroot to determine the presence of wind slab.

    Today, winds are forecast to be easterly and moderate.

    Where they have been strong enough, easterly winds have scoured west slopes and redeposited snow on westerly aspects where windslab is not normally found. 

    The slopes being loaded were previously scoured, and wind hardened, creating a smooth bed surface for new windslab. 

    Wind lips, cornices, and pillows can indicate wind direction and the presence of windslab. 

    Shooting cracks, slabs shifting off small convexities and switchbacks, are signs of reactive windslab. 

    Today, avoid wind loaded start zones over 35º.

    (2/20/2022)

    Southern Bitterroot, touchy windslab on north east aspect

    Photo: Geoff Fast

Avalanche Discussion

Winter is back and might be compensating for the past few weeks of warm weather. It’s COLD out there. Yesterday, temperatures were -8ºF in the Rattlesnake at 1:00 pm, overnight they dropped to -22º and are forecast to stay low through Wednesday morning. The winds are howling, with easterly winds reaching 60mph and sustaining 40mph overnight. Windchill hit -59 ºF at Point 6.

The cold is the biggest risk management issue today. Recreating in temps this cold requires special care to avoid cold injuries and frostbite. The cold will seriously compound any issues that arise, whether it’s gear problems, injury, or avalanche. It's a good reason to keep things mellow and conservative today. 

Since that last avalanche forecast, up to 1.2” SWE, or 14” of snow has fallen. The Seeley Lake region and central Bitterroot were favored, but all regions received a refresh. Crusts from the warm spell are now up to 20” deep, and the new snow is bonding to them well. 

The way eastern winds funnel through the mountains can create drastic differences in windspeed throughout the forecast area, with some areas getting blasted while others are relatively calm. Yesterday, the southern Missions had light winds, while the Swans saw winds to 45mph. Lolo Pass saw 77mph winds at the visitors center, while the southern Bitterroot had light breezes. Because of this, newly developed windslab will vary widely throughout the forecast area. In areas where east winds were strong, expect windslab on west slopes. Where the wind was light, windslab deposited on easterly slopes over the weekend may still be reactive. 

Lolo Pass area still has some reactive buried surface hoar. Hangover Hill presented some alarming ECT propagations and large whumphs over the weekend. Nearby slopes provided inconsistent results on column tests, suggesting patchy distribution of the surface hoar. It’s unlikely to trigger a slide, but it is worth noting. Look for a thin, lower density layer about 20” down in the snow. Propagation in an ECT or whumphing are signs to keep slope angles under 35º.

We love all the public observations we’ve received this year. Many thanks to the folks who’ve sent them in. You can submit observations here. 

We’d like to remind you all that we’ve divided the forecast area into three zones; the Seeley, Rattlesnake, and Bitterroot. Even when the forecast map displays the same hazard rating for all zones, there still may be further zone-specific information in each. It’s worth checking the specific zone where you plan to recreate. 

Ski and ride safe, and stay warm out there.

Regions covered