Posted:
Apr 21, 2018 @ 9:04 am

Good Morning, this is Logan King with a springtime avalanche update.

SPRINGTIME SNOW SAFETY CONSIDERATIONS

Winter has lingered across the region for a while, but spring has finally made an earnest appearance in West Central Montana. The last few days have brought temperatures that are well above freezing. Warm temperatures paired with clear conditions have finally pushed to snowpack into the warm melt-freeze cycles and wet late day conditions that we expect to see this time of year.

The snowpack has entered a predictable cycle which means that avalanche hazards can primarily be managed with timing when and where you choose to travel. In areas where it freezes overnight firm melt-freeze crust will form and will develop into wet avalanche problems as they warm. The southern half of the compass will be the first to go. If you see signs of weakening snow like pinwheels and roller balls you should move to a cooler and shaded aspect. Avoid traveling on or under cornices especially later in the day.

Continually re-evaluate conditions as they will be changing on the scale of minutes, and will do so every day. Don’t be lulled into complacency by the warm and sunny weather. Wet and Glide avalanches are a serious concern this time of year along with cornice failures so stay on your toes and use safe travel protocols if you are out in the mountains.

We will continue to post public observations as long as we receive them and will update information as need be. If you are out recreating in the backcountry, please continue to send us observations by sending an email or use the form available on our website at missoulaavalanche.org. The information provided might keep someone out of trouble.

Ski and ride safe.

READ FULL ADVISORY  

Problem 1 - Wet Loose or Slabs

  • TYPE

    wet-slabs

    Wet Slabs

    Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet slabs can be very destructive.

  • 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.

Wet avalanches are extremely difficult to predict, the best indicator of a rising concern are rollerballs and sloppy surface snow.

Problem 2 - Cornice Failures

  • 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

    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.

Avoid traveling on or under cornices.

Problem 3 - Glide Avalanches

  • 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

    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.

Glide avalanches are incredibly unpredictable, so if you see glide cracks move to different terrain.

FORECAST & OUTLOOK

Spring conditions will lead melt-freeze cycles.

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.