Posted:
Feb 14, 2019 @ 6:52 am

The avalanche danger for the west central Montana backcountry is CONSIDERABLE on wind loaded slopes. All other slopes have a MODERATE danger. Identify wind loaded slopes and avoid them. Careful evaluation is needed to identify features of concern.

Good morning, this is Travis Craft with the West Central Montana Avalanche Center’s avalanche advisory for February 14, 2019. Today’s advisory is sponsored by Yurtski. 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 14 F to 20 F. In the Bitterroot winds are calm. In the northern part of the advisory area, winds are 6 mph and gusting 9 mph out of the ENE. Snotels are reporting between .3 and .7 inches of SWE for the last 24 hours.

Our forecast area has received several new inches of snow over the last 24 hours accompanied by moderate winds. The region will see rising temperatures today and no precipitation during the day.

The primary avalanche problem is wind drifted snow. Winds have loaded leeward slopes. Look for wind slabs on exposed terrain on northwest, northeast, and southeast aspects. These slabs are sensitive to human triggers. Look for smooth rounded pillows and drifts on ridges and cross-loaded slopes. Identify these slopes and avoid traveling on them.

The second avalanche problem is new snow. Look for large loose snow avalanches and storm slabs. We saw several point releases yesterday and saw the new snow start to slab up later in the day. Shooting cracks and natural avalanche activity are red flags of instability. Use small test slopes with low consequences to see how the new snow is bonding to old snow surfaces(video)(video).

The final avalanche problem is persistent slabs. We have weak layers in our snowpack, buried surface hoar, and facets. Dig a pit 3 feet down and see if any of our weak layers are reactive in pit tests.

Bottom line: Today the snowpack is adjusting to the new load of snow. Avoid wind drifted slopes. Dig a pit to see how the new snow is bonding to old snow surfaces and how the weak layers in our snowpack are adjusting to the new load of snow. Use test slopes and lower angle terrain to check the bonding of new snow to old snow surfaces. Pay attention to changing conditions and look for red flags(shooting cracks, natural avalanche activity, and collapsing).

Avalanche and Weather Outlook

Today, look for warming temperatures. The avalanche danger will stay the same today. Snow will enter the forecast area tonight with high snowlines in the Bitterroot.  See the forecast here. New snow and wind will increase the avalanche danger overnight and into Friday.

As always, if you make it out, please, feel free to share, what you find on our public observations page.

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
    NW - Northwest

  • IMAGE

Winds have loaded leeward slopes. Look for wind slabs on exposed terrain on northwest, northeast, and southeast aspects. These slabs are sensitive to human triggers. Look for smooth rounded pillows and drifts on ridges and cross-loaded slopes. Identify these slopes and avoid traveling on them.

Problem 2 - New Snow

  • 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-4

    Possible/Likely

    The likelihood of an avalanche resulting from this problem.

The second avalanche problem is new snow. Look for large loose snow avalanches and storm slabs. We saw several point releases yesterday and saw the new snow start to slab up later in the day. Shooting cracks and natural avalanche activity are red flags of instability. Use small test slopes with low consequences to see how the new snow is bonding to old snow surfaces(video)(video)

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

    5-6

    2-3 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-2

    Unlikely/Possible

    The likelihood of an avalanche resulting from this problem.

We have weak layers in our snowpack, buried surface hoar, and facets. Dig a pit 3 feet down and see if any of our weak layers are reactive in pit tests.

VIDEO

Observations

Observations

FORECAST & OUTLOOK

Today, look for warming temperatures. The avalanche danger will stay the same today. Snow will enter the forecast area tonight with high snowlines in the Bitterroot. See the forecast here. New snow and wind will increase the avalanche danger overnight and into Friday.

 

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.