Posted:
Jan 21, 2017 @ 5:41 am

The current avalanche danger is LOW for the West Central Montana backcountry. Low danger does not mean no danger. Human triggered avalanches are still possible, unstable snow can be found on isolated terrain features.

Good morning, this is Logan King with the West Central Montana Avalanche Center’s avalanche advisory for Saturday, January 21, 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

Conditions this morning continue to be mild with mountain temperatures in the teens to low twenties across the region. Winds are light this morning as Point 6 is recording winds gusting to 18mph out of the east and at Deer Mountain in the southern Bitterroot winds are gusting to 17mph from the south-east. Most snotel sites show no new snow overnight while Twin Lakes in the Bitterroot possibly picked up an inch or two of snow since yesterday afternoon.

Observers near Lost Trail Pass were able to get small windslabs to fail on Thursday and the windslabs will continue to be the primary concern today. Windslabs are small and isolated and may be hard to identify so carefully look for sign of wind transport when choosing where to recreate today. Winds have been anything but consistent this year and unfortunately windslabs can still be found on any aspect due to local variability in the wind, so carefully evaluate which aspects and terrain features are wind loaded while you are traveling.

The secondary avalanche concern today will be persistent slabs. Travis and Matt were in the southern Missions yesterday and found the near surface facets to be reactive in compression tests but they did not propagate in extended column tests. The persistent weak layers will be of greatest concern in areas where the surface snow has settled and formed a slab. Slabs are not widespread but pay attention to how the snow feels underneath you as you travel and if it has a slab like feel to it, take the time to look at what snow structure is underneath.

Finally Temperatures have been warm and what little snow we have seen the last couple days has been wet and heavy. Small wet point releases have been seen throughout the region over the last few days. Be cautious of heavily solar affected aspects that will be more prone to these small wet slides, if you see rollerballs start moving try to find a cooler and dryer aspect to recreate on. Although not large in size these loose wet slides can be dangerous if terrain traps are present. Keep in mind the consequences of even a small slide if there are trees or rocks that you would get carried through or over.

 

Avalanche and Weather Outlook.

A weak disturbance is expected across the region today bringing scattered light snow showers, with minimal accumulations. The subtle change in the weather will not have an effect on the avalanche conditions and the avalanche danger looks to stay the same through today.

We continue to get great public observations, and as always if you get out please feel free to share what you are finding. Your observations are extremely helpful with writing the advisory and keeping track of regional conditions.

The next regularly scheduled advisory will be on Tuesday, January 24, 2017.

Ski and ride safe.

READ FULL ADVISORY  

Problem 1 - Windslabs

  • 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-2

    Unlikely/Possible

    The likelihood of an avalanche resulting from this problem.

Pockets of windslabs are out there and can be triggered under the right conditions.

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.

Near surface facets continue to fail in compression tests and basal facets can still fail in compressions tests as well. Propagation of persistent weak layers is minimal but with how widespread they are there is likely a localized area where a persistent slab is laying in wait.

Problem 3 - Wet Loose

  • TYPE

    loose-wet

    Loose Wet

    Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose-Dry Avalanches,they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose-wet avalanches can trigger slab avalanches that break into deeper snow layers.

  • SIZE

    1-2

    < 1 (Small)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-4

    Possible/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:

    E - East
    SE - Southeast
    S - South
    SW - Southwest
    W - West

With warm temps and a heavy wet snow surface small wet loose slides will be likely on heavily solar affected slopes.

VIDEO

FORECAST & OUTLOOK

Scattered snow shows today with minimal accumulation and mild temperatures.

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.