Dec 20, 2018 @ 6:14 am

For wind loaded terrain the avalanche danger remains HIGH across the West Central Montana backcountry. The danger on non-wind loaded terrain is considerable.  Very dangerous avalanche conditions exist as large avalanches are possible in many areas. Cautious route finding is essential and travel in and around avalanche terrain is not recommended.

Good morning, this is Logan King with the West Central Montana Avalanche Center’s avalanche advisory for Thursday, December 20th, 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

Mountain temperatures this morning are in the twenties as of 4 a.m. Overnight a trace to an inch of snow fell at some locations but overall not much snow has fallen since mid-day yesterday. Winds are light out of the SSE-SE at about 8 mph and gusting to 10 mph.

Wind slabs are the primary avalanche concern today. Yesterday we remotely triggered a wind slab in  the Rattlesnake (pic, video), and observed another skier triggered windslab while observers in the Bitterroot triggered a winds slab as well (pic). The big take away is wind slabs are wide spread, very sensitive to triggers, and are not something you want to be on, below, or near for that matter. If you are seeing signs of wind loading you can also expect to hear/see whumpfing, shooting cracks, collapsing and remote triggers; all of which should point you away from wind affected terrain.

Buried surface hoar continues to be reactive in stability tests and will make persistent slabs the secondary concern. The buried surface hoar is breaking down and is not as widespread as last week but is very reactive in stability test but can still be found on at many locations (video). Take the time to dig a pit to see if the persistent weak layers are present and reactive.

Avalanche and Weather Outlook

Snowfall should be minimal today with the next round of snow impacting the region tonight and into Friday (forecast). Strong winds are expected to usher in the next round of precipitation so expect to see strong winds develop through the day today. The lull today doesn’t appear to be long enough to let avalanche conditions settle down so they should remain the same leading into the next storm.

Join us tonight at Big Sky Brewing from 6-8 pm for Beers with Forecasters. Come have a beer and talk to your local forecasters about avalanche conditions, or ask a question you have been pondering all season. This is great opportunity to practice you rescue skills as well in the new beacon park at Big Sky Brewing.

If you do make it out into the hills 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 (Large)

    The potential size of avalanche resulting from this problem.



    Very Likely

    The likelihood of an avalanche resulting from this problem.


Stiff wind slabs on top of weak snow are very reactive across the advisory area.

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


    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.


Buried surface hoar readily propagates in stability tests and with the addition of weak faceted snow near the base, persistent slabs continue to be a significant concern.




  • Danger Trend


    Same Danger

  • Area Forecast


Strong winds today will develop today leading up to the next round of precipitation tonight and into tomorrow.

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.