Posted:
Jan 5, 2018 @ 6:06 am

Good morning, this is Logan King with the West Central Montana Avalanche Center’s weather update for January 5th, 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 across West Central Montana are in the low 30’s this morning with many locations already above freezing. Precipitation has been minimal with a few snotels showing and addition of .1-.2 inches of SWE. Winds at Point 6 are 17 mph gusting to 24 mph from the W. Further south at Deer Mountain, winds are 7 mph gusting to 12 mph from the SSW. Weather conditions will be similar to yesterday until moisture returns to the region late today. The snow level is expected to be fairly high through Saturday morning. 

Conditions have not changed much over the last few days and the main avalanche concerns continue to be wind slabs and deep persistent slabs. Wind slab activity continues across the region above 6,500 feet. Deep persistent slabs are hard to trigger but will be high consequence events. Carefully evaluate terrain to identify areas of wind loading and potential trigger zones for deep persistent avalanches.

If you are out in the backcountry, please send us your observation, these are very helpful in producing the advisory. The next advisory will be issued tomorrow January 6th, 2018.

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

    4-5

    2 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-5

    Likely

    The likelihood of an avalanche resulting from this problem.

Wind slabs above 6,500 feet continue to be reactive.

Problem 2 - Deep Persistent

  • TYPE

    deep-persistent-slabs

    Deep Persistent Slabs

    Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground.  The most common persistent weak layers involved in deep, persistent slabs are depth hoar, deeply-buried surface hoar, or facets surrounding a deeply-buried crust. Persistent, Deep-Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. They commonly develop when Persistent Slabs become more deeply-buried over time.

  • SIZE

    6-7

    3 (Large-Very Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    The likelihood of an avalanche resulting from this problem.

The Thanksgiving crust is difficult to trigger but has been involved in a few recent natural and human triggered avalanches producing large dangerous avalanches.

FORECAST & OUTLOOK

Mild conditions today will shift to storms tonight through the weekend.

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.