Avalanche forecast

Rattlesnake

West Central Montana Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 3 years ago.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

Highlights

Dangerous avalanche conditions exist due to new snow accompanied by strong wind. Triggering an avalanche in wind loaded terrain is very likely. Avalanches may be triggered from a distance or fail naturally. Extreme cold will complicate rescue efforts. Stick to low angle terrain that is free of overhead hazards.

Avalanche problems

  • Wind Slabs

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

    You are very likely to trigger a large wind slab avalanche today. New slabs have continued to build on previous wind slabs formed throughout the week. Plenty of new snow will be available for transport throughout the day today by strong gusts of wind. With shifting wind directions, you may encounter wind slab formation on atypical slopes (south and west) at upper elevations. You may also encounter wind slab formation lower down on slopes than usual. Slabs will be hard and can break well above you. Expect to find wind-drifted snow on or just below ridgelines, on saddles, and in cross-loaded gullies.

    Wind slabs may rest on persistent weak layers and act similarly to persistent slab avalanches. Fresh snow will conceal older wind slab formation in many areas. Be aware of the terrain above and around you, as you can trigger an avalanche from a distance (remote triggering). A hard slab avalanche will be difficult to escape. Signs of instability include whumpfing, collapsing, shooting cracks, and recent avalanches. Travel in low angle, wind sheltered terrain today well away from steep slopes.

  • Persistent Slabs

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

    Human triggered persistent slab avalanches are likely today. North and east aspects at middle and upper elevations all have some form of buried weak layers, including surface hoar, facets, and depth hoar. Recent snow has added stress to older, weak snow within the snowpack. The likelihood oftriggering a deeper avalanche on weak snow near the ground increases today. Wind slab avalanches could step down to the weak facets near the ground. Avalanches this size would be large and destructive. 

    Red flags include whumpfing, collapsing, shooting cracks, and recent avalanches. Be aware of terrain above and around you, as you can trigger an avalanche from a distance (remote triggering). It is worth your time to dig down into the snowpack to look for poor snowpack structure (harder snow over soft) but don’t be fooled by a lack of unstable results in snowpit tests. The best way to manage the hazard today is avoidance. Stick to low angle slopes without steep terrain overhead.

Avalanche Discussion

We have changed our forecasting schedule. Starting with yesterday’s forecast, we will be publishing consecutive forecasts on Thursdays, Fridays, Saturdays, and Sundays. Check out this blog post for further information.

New 24 hour totals:

North Fork Jocko SNOTEL (Seeley Lake): 1 inch with .10 inches of SWE (snow water equivalent)

Stuart SNOTEL (Rattlesnake): 7 inches with .70 inches of SWE

Lolo Pass SNOTEL (Northern Bitterroot): 8 inches with .60 inches of SWE

Twin Lakes SNOTEL (Central Bitterroot): 9 inches with 1.30 inches of SWE

Saddle Mountain SNOTEL (Southern Bitterroot): 5 inches with .50 inches of SWE

Updated storm totals:

North Fork Jocko SNOTEL (Seeley Lake): 13 inches with 1.7 inches of SWE ( snow water equivalent)

Stuart SNOTEL (Rattlesnake): 17 inches with 1.7 inches of SWE

Lolo Pass SNOTEL (Northern Bitterroot): 25 inches with 2.3 inches of SWE

Twin Lakes SNOTEL (Central Bitterroot): 37 inches with 4 inches of SWE

Saddle Mountain SNOTEL (Southern Bitterroot): 14 inches with 1.6 inches of SWE

This puts the new snow total for the week at over 3 feet in the southern Bitterroot and over 1 foot in other parts of our forecast region. This is a lot of new snow that was accompanied by a lot of wind. Avalanche conditions are very dangerous. Natural avalanches are possible, but human-triggered avalanches are very likely.

Wind slabs are widespread and reactive. They have formed in places you might not normally encounter. They are capable of stepping down into weak layers near the ground. The snowpack in the central Bitterroot is especially overloaded. Heed extra caution in this zone.

Weak faceted snow, surface hoar, and depth hoar are all buried within the snowpack. These layers have not yet adjusted to this new load and are showing signs of instability. This observation from yesterday reported a very easy extended column test result (ECTPV) that failed in a layer of weak faceted snow.

The new slab of snow is dense and cohesive in many areas. Like this large avalanche triggered in the Seeley Lake zone on Wednesday, it is possible to trigger an avalanche from a distance (remote trigger). Slabs can propagate a wide distance and run far down slopes. Dense and hard slabs are destructive and difficult to escape. The debris is also difficult to travel over during an avalanche rescue.

The snowpack is slowly building on lower elevations. As much of the new snow fell on dirt, there are not currently persistent weak layers with a slab sitting on top. For this reason, low elevations are at a low danger for the day. Continue to keep an eye out for ground hazards such as downed logs, stumps, and rocks. They may exist under new snow and be obscured from view.

Temperatures may reach historic lows today. Most of western Montana will have wind chills capable of causing frostbite in under 10 minutes. Extreme weather can make an avalanche incident go from bad to worse in a matter of minutes. Be prepared with extra layers, food, and water.

It is imperative that you stay alert if you venture into the backcountry today. The best way to manage the hazard is to avoid avalanche terrain. Give a wide berth when traveling near or below steep slopes.

Please considersubmitting an observation of what you see in the mountains. Even simple photos and notes about the weather help forecasters make more accurate forecasts.

Ski and ride safe!

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