Posted:
Mar 4, 2017 @ 7:05 am

The current avalanche danger in the West Central Montana backcountry is considerable on steep wind loaded terrain. Careful snowpack evaluation to identify wind loaded areas will be critical as human triggered avalanches are likely. The avalanche danger on all other terrain is currently moderate.

Good morning, this is Logan King with the West Central Montana Avalanche Center’s avalanche advisory for March 04, 2017. 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 range from 28-33 degrees as another active weather system works its way into West Central Montana. Overnight an additional trace-3 inches of snow fell and added up to .2 inches of SWE. Currently, winds at Point 6 are 17mph gusting to 35mph from the WSW, and at Deer Mountain are 8mph gusting to 14mph from the S.

Travis and I rode around Seeley Lake yesterday and found significant signs of wind slab development above 6,000ft. We also saw an old crown and flank from a significant natural wind slab failure in the last 2-3 days. With a large load of light snow for transport and a couple of windy days, wind slabs have grown and will be suspect. Avoid steep terrain over 6,000 ft that shows signs of wind loading.

Observers near Lost Trail pass yesterday found storm slabs to be the greatest concern on non-wind loaded terrain. Travis and I also observed storm slabs to be a secondary concern. A density change in the storm snow in the Seeley area propagated in stability tests yesterday. This density change is from a brief warm up during the last storm cycle. This will need a another day or two to finish bonding but a new storm slab will start forming today. Storm slabs vary in thickness and cohesion across the region, take a few minutes to dig and see how the snow is bonding and to identify if the new load is adding to the concern before committing to avalanche terrain.

Avalanche and Weather Outlook

Snow is expected through the day today and temperatures look to cool as the next cold front pushes into the region later today and into tonight. Snow totals of up to a foot are in the forecast over the next few days. The avalanche danger will be increasing on all terrain today and through the weekend.

If you are out in the backcountry, please send us your observations, these are very helpful in producing the advisory. Travis will issue the next advisory on March 07, 2017.

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-5

    Likely

    The likelihood of an avalanche resulting from this problem.

  • ADDED DANGER

    Increased Slope Danger

    Increased/Added Danger

    There is an increased risk of avalanches on these slopes:

    N - North
    NE - Northeast
    E - East
    SE - Southeast
    S - South
    NW - Northwest

  • IMAGE

Wind slabs have formed above 6,000ft on leeward terrain and will be sensitive to artificial triggers today.

Problem 2 - Storm Slab

  • 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

    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.

Density changes in the storm slab have been found to propagate in stability tests.

VIDEO

FORECAST & OUTLOOK

Increasing snow today and into tonight will continuing through the start of the week.

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.