Posted:
Feb 3, 2018 @ 6:19 am

The current avalanche danger is Considerable in the west central Montana backcountry.  Natural avalanches are possible, and human-triggered avalanches remain likely. Cautious route finding and conservative decision making are essential for backcountry travel today.

Good morning, this is Travis Craft with the West Central Montana Avalanche Center’s avalanche advisory for February 03, 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 range from 29 F to 34 F in the region.  In the Bitterroot winds are 11 mph with gusts of 19 mph out of the SW.  In the northern part of the advisory area, winds are reading 22 mph with gusts of 24 mph out of the SW.  Snotels are not reporting this am. Most data is from midnight and before.  Rain has fallen to roughly 6000 feet.

Logan and I took the sleds to the southern Missions yesterday near Seeley Lake.  We found 6 new inches of snow and warming temperatures throughout the day. We observed active wind transport of snow and cornice growth. We also saw wet loose releases in the afternoon.

The main avalanche problem is wind slabs. These slabs are large and getting stressed by warming temperatures and the addition of new snow.  Look for rounded pillows of snow near ridgelines and on cross-loaded slopes. Recognize signs of instability such as cracking in the surface snow. Avoid traveling on or under wind loaded slopes.

The second avalanche problem is wet loose releases. When slopes start to produce roller balls or pinwheels, it is time to move to another aspect.

The final avalanche concern is persistent slabs. There are some weak layers in the snowpack that could become reactive with the additional loading of snow or rain. Dig a pit and see how reactive these weak layers are to the new load and warming temperatures.

Overall with the addition of rain and warming temperatures the snowpack can change rapidly. Look for bullseye data today; roller balls, shooting cracks and collapsing, these will identify changing snowpack conditions. There is a lot of uncertainty in how high the rain will fall; therefore today conservative decision making is essential. Pay close attention today as conditions can change quickly in a matter of minutes to hours with rain on snow events.

Avalanche and Weather Outlook

Today rain and snow mix to 6000 feet and above possibly. These conditions will lead to increasing avalanche danger today. See the forecast here.

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.

  • IMAGE

These slabs are large and getting stressed by warming temperatures and the addition of new snow.  Look for rounded pillows of snow near ridgelines and on cross-loaded slopes. Recognize signs of instability such as cracking in the surface snow. Avoid traveling on or under wind loaded slopes.

 

Problem 2 - Loose Wet

  • 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

    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.

  • IMAGE

The second avalanche problem is wet loose releases. When slopes start to produce roller balls or pinwheels, it is time to move to another aspect.

 

Problem 3 - 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

    4-5

    2 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    The likelihood of an avalanche resulting from this problem.

  • IMAGE

There are some weak layers in the snowpack that could become reactive with the additional loading of snow or rain. Dig a pit and see how reactive these weak layers are to the new load and warming temperatures.

VIDEO

Ground Hog Day Observations

02/02/2018 Observations

FORECAST & OUTLOOK

Today rain and snow mix to 6000 feet and above possibly. These conditions will lead to increasing avalanche danger today. See the forecast here.

 

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.