Posted:
Mar 11, 2021 @ 6:45 am

The avalanche danger in the west central Montana backcountry is MODERATE on north facing slopes above 6500 ft. All other slopes are Low.  Evaluate snow and terrain carefully.

Good Morning. This is Travis Craft with the West Central Montana Avalanche Center advisory on Thursday, March 11, 2021. This advisory is sponsored by the Big Sky Brewing Company. This advisory does not apply to operating ski areas and expires at midnight tonight. The USDA Forest Service is solely responsible for its content.

Weather and Snowpack

Temperatures range from 8 to 16 degrees this morning. Winds will be light gusting to the teens today out of the West. It will be warm and sunny today.

Yesterday, we found dry snow on North facing slopes throughout the advisory area. Weak snow still failed in pit tests on these slopes. On all other aspects, there is a supportable crust, and the snowpack has consolidated. The likelihood of triggering these facets is going down, but the consequences of triggering this layer are high.

Cornices and glide cracks will be with us for the rest of the season. Cornices are sagging and should be given a wide berth. Avoid glide cracks. Take small steps into riding steeper and steeper terrain. If you feel a supportable crust, it will be less likely to trigger a persistent weak layer. On North facing slopes greater than 35 degrees above 6500 ft, it is possible to trigger a persistent weak layer.

Today with warming temperatures and light cloud cover, look for loose wet activity on sun-exposed terrain. When roller balls show up, move to shadier aspects.

Bottom Line

Choose slopes with a supportable crust to minimize the likelihood of triggering a persistent weak layer. Choose slopes less than 35 degrees if there is not a supportable crust.

Avoid traveling under large cornices and give them a wide berth on ridges. If roller balls show up, move to shadier aspects or head home. Avoid glide cracks. 

Carry a beacon, shovel, and probe. Reassess conditions throughout the day and stay alert for signs of instability. Dig pits. Look for red flags.

Remember: the danger rating and avalanche forecast are meant to give you baseline information to use in your travels, but YOU get to make the decision whether riding or skiing specific terrain is a good idea or not.

Upcoming Education Events

Please visit our education page for an up-to-date list of regional educational events and course offerings. Below are a few select events and opportunities to check out.

Public Observations

Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. This online forum is a great resource to glean information about current conditions.

You can now text us your observations to (406) 219-5566 when you don’t have time to fill out the observations page. Texted observations won’t get posted on the website, but will be used in the development of the forecast.

Ski and ride safe.

READ FULL ADVISORY  

Problem 1 - Wet Snow

  • TYPE

    loose-wet

    Loose Wet

    Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose-Dry Avalanches,they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose-wet avalanches can trigger slab avalanches that break into deeper snow layers.

  • SIZE

    3-4

    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-2

    Unlikely/Possible

    The likelihood of an avalanche resulting from this problem.

  • ADDED DANGER

    Increased Slope Danger

    Increased/Added Danger

    There is an increased risk of avalanches on these slopes:

    E - East
    SE - Southeast
    S - South
    SW - Southwest
    W - West

As the sun comes out and produces roller balls it is time to move to shadier aspects. Timing is everything with spring conditions. When the roller balls show and you start to punch into the snowpack head home or seek out shade.

Cornices are sagging. Avoid being under cornices during the day. Give these giants a wide berth on ridges.

Problem 2 - Persitent Weak Layers

  • TYPE

    persistent-slabs

    Persistent Slabs

    Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks.  Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Persistent, Deep-Slab.

  • SIZE

    5-6

    2-3 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-2

    Unlikely/Possible

    The likelihood of an avalanche resulting from this problem.

  • ADDED DANGER

    Increased Slope Danger

    Increased/Added Danger

    There is an increased risk of avalanches on these slopes:

    N - North
    NE - Northeast
    NW - Northwest

North facing slopes still have weak layers that are propagating in pit tests. On slopes with supportable crusts you will be less likely to trigger these weak layers.

VIDEO

Lost Horse 03/10/2021

GALLERY

Lolo surface hoar, 03:10:2021
Lolo surface hoar, 03:10:2021
Mt. Fuji snowpack, 03:10:2021
Mt. Fuji snowpack, 03:10:2021
Pit location and wind clues
Pit location and wind clues
S Missions Cornice 03/08/2021
S Missions Cornice 03/08/2021
Lappilake-suncrust-03-08
Lappilake-suncrust-03-08

Observations 03/10/2021

FORECAST & OUTLOOK

Expect the avalanche danger to rise as the sun comes out and warms slopes. Look for the snowpack to refreeze overnight. This look to be the trend over the next couple of days. See the forecast.

This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.