Posted:
Jan 17, 2017 @ 6:58 am

The current avalanche danger is LOW for the west central Montana backcountry. Human triggered avalanches are still possible in isolated terrain.

Good morning, this is Travis Craft with the West Central Montana Avalanche Center’s avalanche advisory for January 17, 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 range from 13 F to 26 F in the region. Winds are 10 mph out of the S in the Bitterroot. Point Six, in the northern part of the advisory area, winds are reading 22 mph with gusts of 32 mph out of the WSW. The forecast area received 0 to 1 inches of new snow in the last 24 hours. The new snow had SWE’s ranging from 0 to .2 inches of water.

Steve and I took the sleds into the Crooked Fork around Lolo Pass yesterday.  Logan went to Crystal Theater.  Dudley was at Yurtski in the southern Swan over the weekend teaching a level 1.  The persistent weak layers in our snowpack are gaining strength.  The high and dry weather has made for some good touring, but all observers reported large surface hoar growth on all aspects.  This will be our next layer of concern.

The first avalanche problem is wind slabs.  Remember identify wind slabs and avoid them. These slabs are on many different aspects, and some slopes are cross-loaded due to the changes in wind direction over the last couple of days.  We had two great public observations from the weekend with wind slabs. Click on the links to see them.  One of the slabs was human triggered, and the other was natural.

The second avalanche problem is persistent slabs. There are two layers (1.) 2 feet from the surface of near surface facets and (2.) the basal facets on the ground. The layers are gaining strength. Dig a pit to assess these facets before committing to any steep slope.

These avalanche problems are in isolated terrain.  Low avalanche danger still means human triggered avalanches are still possible.  Assess slopes carefully and identify any concerns.

Avalanche and Weather

The precipitation forecast maintains a slowing trend, so light snow is possible by this afternoon, but the majority is not expected to begin until Wednesday morning.  The avalanche danger will increase with the precipitation.  The main concern will be the surface hoar that is being buried by the new snow.

We have been getting a lot of public observations, thank you.  If you are out in the backcountry, please send us your observations, these are very helpful in producing the advisory.

The West Central Montana Avalanche Center would like to extend our deepest condolences to friends and families of all involved in the avalanche fatality in Southern Glacier National Park on Thursday, January 05, 2017.  Here is the link from the Flathead Avalanche Center of the full report.  Logan will issue the next advisory on Thursday, January 19, 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

    2-3

    1 (Small)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-2

    Unlikely/Possible

    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

  • IMAGE

Wind slabs exist in isolated pockets in the advisory area.

Problem 2 - Persistent Slabs

  • TYPE

    persistent-slabs

    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

    3-4

    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-2

    Unlikely/Possible

    The likelihood of an avalanche resulting from this problem.

  • IMAGE

Dig a pit before committing to any steep terrain.

Two layers of concern:

1. A Layer of near surface facets below a crust 30 cm from the surface.

2. The basal facets on the ground.

VIDEO

Observations MLK

FORECAST & OUTLOOK

The precipitation forecast maintains a slowing trend, so light snow is possible by this afternoon but the main precipitation is not expected to begin until Wednesday morning. The avalanche danger will increase with the new loading. The main concern will be the surface hoar that the new snow will be falling on.

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.