Posted:
Dec 15, 2016 @ 5:11 pm

An avalanche warning is in effect for the west central Montana backcountry.  The avalanche danger is now HIGH on terrain steeper than 30 degrees.  Natural avalanches are likely and human triggered avalanches are very likely.  Travel in avalanche terrain is not recommended.

Good afternoon, this is Travis Craft, with an avalanche warning for Thursday, December 15, 2016. This avalanche warning will expire at 5:00pm on December 16, 2016.  The warning will be extended or terminated at that time.

This information is the responsibility of the Forest Service and does not apply to operating ski areas.

Snow and Weather 

With the addition of a large amount of new snow and wind to the poor structure of the snowpack we are issuing an avalanche warning.  Travel in avalanche terrain is not recommended.

We will be in the field tomorrow and will continue the warning tomorrow at 5pm or terminate it.

Ski and ride safe.

READ FULL ADVISORY  

Problem 1 - 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

    5-6

    2-3 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-6

    Likely/Very Likely

    The likelihood of an avalanche resulting from this problem.

 

Problem 2 - 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

    6-7

    3 (Large-Very Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-7

    Very Likely

    The likelihood of an avalanche resulting from this problem.

 

Problem 3 - Strom Slabs

  • TYPE

    storm-slabs

    Storm Slabs

    Release of a soft cohesive layer (a slab) of new snow which breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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

    5-6

    2-3 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-6

    Likely/Very Likely

    The likelihood of an avalanche resulting from this problem.

 

FORECAST & OUTLOOK

Increased winds.

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.