Posted:
Apr 1, 2020 @ 6:52 am

This is Travis Craft with an end of season update. The West Central Montana Avalanche Center issued its last advisory yesterday, March 31, 2020. The operating season for the center has come to a close. If you are going to recreate in the backcountry, it is time to become your own forecaster. 

There is a multitude of resources available to help with trip planning. Utilizing these resources can help you when mapping out routes and keeping tabs on weather and conditions. Familiarize yourself with local telemetry resources, cameras, and apps to monitor conditions.

Check the uphill travel policies of each ski area you plan to visit. Remember, when the ski resort is closed, there is no ski patrol for rescue or avalanche mitigation. The rules for travel and riding are the same for the backcountry. 

Traveling in the backcountry this time of year can be very dynamic. Winter conditions can be found at higher elevations with spring conditions at lower elevations. Pay attention to weather changes and remember to reassess the snowpack throughout the day. Travel one at a time in avalanche terrain, carry a beacon, shovel, and probe, and stay alert for signs of instability. Dig a pit. Look for red flags.

Here is a link to some excellent online e-learning material. KBYG

Avalanche Problems and Ways to Combat Them

Wet Avalanche Problems

As the snow heats up during the day, be aware of the increasing likelihood of wet loose avalanches. Signs that the snowpack is warming include pinwheelsrollerballs, or if you are sinking up past your boots in heavy, wet snow. 

Rain on snow events and nights without freezing temperatures lead to wet slab avalanche problems. These are hard to predict. The best way to avoid these is heading home when the rain starts and avoiding travel on or below steep slopes when temperatures do not refreeze overnight.

Glide cracks are opening in isolated areas of the Bitterroot and Missions. These are the result of the entire snowpack sliding on a wet ground surface, and they can slowly open for weeks at a time. They can fail suddenly and unpredictably, producing avalanches the full depth of the snowpack. Stay well away from slopes where glide cracks are present.

New Snow Problems

Loose snow avalanches and Storm slabs: Use small test slopes to see how the new snow is bonding to old snow surfaces. Use hand pits and pole tests to assess the new snow. Look for cracks from your skis or machine to identify storm slabs.

Wind Problems

Wind slabs: Watch for blowing snow and rounded, textured, drifts. Shooting cracks are a sign of unstable wind slabs.

Cornices will continue to be suspect for the remainder of the season until they have all broken down. Warm temperatures and more loading can lead to cornice failure. Give them a wide berth.

Old Snow Problems

Persistent slab avalanches: Dig a pit and look for stripes in the snow to identify weak layers. Perform a pit test to see how reactive these layers are. Choose a shallow spot to see if you have weak sugary snow at the bottom of the snowpack if you do choose another slope.

Bottom Line

Be diligent with your snowpack assessments and trip planning. Look for terrain traps. Dig a pit. Check the weather forecast. Be your own forecaster.

We will continue posting observations throughout the spring. If you get out, please take a minute to fill out the observation form on our website (missoulaavalanche.org), or shoot us a quick email at [email protected] Thank you to everyone who has sent in observations this year.

Please take a moment to read this message from Missoula Avalanche, Greater than the Sum of Our Parts.

Finally, I would like to extend our most sincere thanks to the fantastic community whose continued support makes our avalanche center and educational opportunities possible. Thank you to all of the supporters, sponsors, donors, partners, and our excellent board, who has helped make the center what it is today.

Ski and ride safe.

 

READ FULL ADVISORY  

Problem 1 - New Snow

  • 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.

Storm Slabs and Loose Dry.

Problem 2 - 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-3

    Possible

    The likelihood of an avalanche resulting from this problem.

Loose Wet and Wet Slabs

Problem 3 - Cornices

  • TYPE

    cornices

    Cornices / Cornice Fall

    Release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the down-wind side. They range from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (~10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice fall can entrain loose surface snow or trigger slab avalanches.

  • SIZE

    4-5

    2 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    The likelihood of an avalanche resulting from this problem.

Cornices are loosing strength and can not be trusted for the remainder of the season.

Problem 4 - Glide

  • TYPE

    glide-avalanche

    Glide Avalanches

    Release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. The are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

    Predicting the release of Glide Avalanches is very challenging. Because Glide Avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide Avalanches.

  • SIZE

    4-5

    2 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    The likelihood of an avalanche resulting from this problem.

Glide avalanches are best managed with avoidance. If glide cracks are present find different terrain to travel on.

Problem 5 - Persistent Slabs

  • 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

    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.

Dig a pit and look for stripes in the snow to identify weak layers. Perform a pit test to see how reactive these layers are.

Problem 6 - Wind Slabs

  • TYPE

    wind-slabs

    Wind Slabs

    Release of a cohesive layer of snow (a slab) formed by the wind.  Wind typically erodes snow from the upwind sides of terrain features and deposits snow on the downwind side.  Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

  • 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.

 Watch for blowing snow and rounded, textured, drifts. Shooting cracks are a sign of unstable wind slabs.

VIDEO

FORECAST & OUTLOOK

Get 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.