Posted:
Jan 8, 2018 @ 6:29 am

Good morning, this is Logan King with the West Central Montana Avalanche Center’s weather update for January 8th, 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

Most of the region did not receive snow yesterday or last night, but a few snotels did pick up 1-2 inches. Mountain temperatures this morning are in the upper twenties to low thirties. Winds have increased in the Southern Bitterroot to 14 mph and are gusting to 21 mph from the SE. In the northern portion of the advisory area winds remain calm.

The snowpack continues to stabilize but the deep persistent slab can still be triggered and result in large avalanches. Wind slabs and deep persistent slabs continue to be the main concern. Take the time to identify if these layers are present and what the possibility is of triggering an avalanche. Carefully consider the consequences of an avalanche before traveling on or in avalanche terrain.

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 9th, 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

    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.

Above 6,500 feet.

Problem 2 - Deep Persistent Slabs

  • 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-2

    Unlikely/Possible

    The likelihood of an avalanche resulting from this problem.

Thanksgiving crust with small facets on top.

FORECAST & OUTLOOK

Mild and calm today before the next system moves in 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.