Posted:
Mar 6, 2021 @ 6:27 am

The avalanche danger in the west central Montana backcountry is moderate. Evaluate snow and terrain carefully.

Good Morning. This is Travis Craft with the West Central Montana Avalanche Center advisory on Saturday, March 6, 2021. This advisory is sponsored by the Trail Head. 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 22 to 38 degrees this morning. Temperatures froze overnight in all locations except in the Rattlesnake at higher elevations. This will lock up low elevation and mid-elevation snowpacks. Winds are predicted to be gusty into the 20’s today out of the SW. Winds will help keep the snowpack cool. Cloud cover is expected with the front moving in today. Yesterday, we found N slopes above 7000 ft to be dry. Expect to find a melt-freeze crust today on all other aspects as you travel, getting thinner as you gain elevation. Facets failed in tests above 7000 ft in the Central Bitterroot. Rollerballs were observed from Lost Trail Pass to the Rattlesnake on multiple aspects except for true North. In Lost Horse, we observed several Glide avalanches that failed in the previous days. The Rattlesnake pit tests show the snowpack is gaining strength.

Today will have variable conditions. The avalanche danger is MODERATE. Be mindful of changing conditions as you change aspect and gain elevation. Avoid traveling under glide cracks. Pay attention to the snow surface. Is it wet or dry? How thick is the crust? Investigate layers you find in the snow and see if they are reactive in pit tests. Look for rollerballs and move to a different aspect if you see them. Be on the lookout for small areas of wind drifted snow on ridges and terrain features.

Bottom Line

Do not let your guard down. Investigate the snowpack today and see how it changes with aspect and elevation. Choose slopes less than 30 degrees. The persistent weak layers are gaining strength but cannot be ruled out. Seek shaded slopes that are low angle.

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

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.

Special Announcements

The mountains are busier than ever before, with new and veteran backcountry users enjoying the goods. To celebrate the snowfall and help ensure everyone has the information needed to enjoy the mountains and return home safely, we bring you Loving La Niña! This virtual fundraising event includes two outstanding gear packages and two ways to enter to win. Please click HERE for more information about this exciting event. All proceeds benefit west-central Montana’s avalanche forecasting and education programs. Together, we can save lives and continue creating the most fun, safe, and responsible backcountry community possible. Spread the word, and spread the love for La Niña!

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 - Loose Dry and Wet

  • TYPE

    loose-dry

    Loose Dry

    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-3

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

Loose dry on North aspects. Loose wet on other aspects. Roller Balls are a red flag to choose a different slope.

 

Problem 2 - Persistent Weak Layer

  • 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-3

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

While stability has improved in many areas we still are seeing propagation on near surface facets, buried surface hoar, and the January 13 crust/facets combo. It is possible to trigger an avalanche on these surfaces.

Mid elevations and areas that are shallow have weak faceted snow as the base. These have been collapsing under the weight of skiers and we are seeing propagation in tests. It is possible to trigger these deeper layers. Shallower avalanches or cornice fall may step down to these deep persistent layers causing large destructive slides.

Where depth hoar, basal, or near surface facets exist, avoid slopes over 30º and provide wide margins below and adjacent to avalanche slopes.

GALLERY

Millpoint-rollerballs-03-05
Millpoint-rollerballs-03-05
Rattlesnake snowpack, north aspect, 03:05:2021
Rattlesnake snowpack, north aspect, 03:05:2021
Lost Horse 03/06/2021
Lost Horse 03/06/2021
20210305LostTrailBC-Pit
20210305LostTrailBC-Pit
Point 6 study plot-05-Mar
Point 6 study plot-05-Mar

Observations 03/05/2021

FORECAST & OUTLOOK

Cold front today. Temperatures continue to drop. Light precipitation over the next couple of days. Look for the avalanche danger to stay the same. 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.