Dec 30, 2018 @ 6:48 am

The current avalanche danger is Considerable for the West Central Montana backcountry. A significant load of new snow and strong winds are creating dangerous avalanche conditions as human triggered avalanches are likely today.

Good morning, this is Logan King with the West Central Montana Avalanche Center’s avalanche advisory for Sunday, December 30th, 2018.  This danger rating does not apply to operating ski areas, expires at midnight tonight and is the sole responsibility of the U.S. Forest Service.

Weather and Snowpack

Since yesterday morning 4-10 inches of snow has fallen across the advisory area. The new snow has deposited 0.4-0.9 inches of SWE. Winds were out of the SW yesterday and around 5pm began gusting to 40-50 mph and were sustained in the 20’s. Winds shifted early this morning to the WNW and have settled but will ramp back up again and shift later today as the cold front moves through. Mountain temperatures are in the mid 20’s to low 30’s Fahrenheit this morning.

As expected, the current storm has notably increased the avalanche danger since yesterday. The new snow and strong winds are creating dangerous avalanche conditions. A lot of new snow is available for transport and is forming large dangerous Wind slabs. The new wind slabs will easily be triggered today and travel on or around wind loaded terrain is not advised.

The Persistent  slabs are becoming increasingly reactive as well. The locations that have faceted snow and and buried surface hoar will be strained under the new load. Be cautious of locations with weak snow structure as they will need a day or two to adjust to the new load. With lots of new surface snow it will be possible to create small sluff avalanches that then act as triggers for the week layers deeper in the snowpack.

Conditions have drastically changed over the past 24 hours and will require an increased consideration of avalanche potential. Human triggered slides are likely, so use cautious route finding and make conservative decisions today as the snow will need some time to settle and adjust.

Avalanche and Weather Outlook

The mountains around West Central Montana remain under a Winter Storm Warning for continued snow and strong winds today. The new snow and strong winds will keep the avalanche danger trending upward. Look for the wind to shift to a more Northerly or Easterly flow late today as a cold front works into the region. The snow will begin to taper off as the week begins but cold temperatures are poised to set up for the beginning of the week (forecast).

If you get out into the mountains feel free to share what you see on our public observations page. They are not only helpful to your community but extremely helpful to us.

Ski and ride safe.


Problem 1 - Wind Slabs

  • TYPE


    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


    2-3 (Large)

    The potential size of avalanche resulting from this problem.



    Likely/Very Likely

    The likelihood of an avalanche resulting from this problem.

Strong winds and ample snow for transport are creating large touchy wind slabs.

Problem 2 - Persistent Slabs

  • TYPE


    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 (Large-Very Large)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.

Areas with weak snow structure will struggle under the new load, especially where denser storm slabs exist.


Strong winds and snow will continue today.

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.