Posted:
Feb 1, 2018 @ 6:42 am

The current avalanche danger is moderate in the west central Montana backcountry. Human triggered avalanches are possible.  Heightened avalanche conditions exist on specific terrain features.  Evaluate snow and terrain carefully and identify features of concern.

Good morning, this is Travis Craft with the West Central Montana Avalanche Center’s avalanche advisory for February 01, 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 11 F to 24 F in the region.  In the Bitterroot winds are 8 mph with gusts of 10 mph out of the South.  In the northern part of the advisory area, winds are reading 4 mph with gusts of 8 mph out of the SW.  The forecast area received 4 to 16 inches of new snow in the last 48 hours.

Logan and I went to Twin Lakes in the central Bitterroot yesterday.  We found 14 new inches of light, low-density snow.  We saw cornice development from the last week of winds and, saw wind loaded slopes near ridge tops and some terrain was cross-loaded. Our weak layers did not propagate in stability tests.  Overall the snowpack is strengthening.

The primary avalanche problem is wind slabs.  Look for rounded pillows of snow near ridgelines and on cross-loaded slopes. Recognize signs of instability such as cracking in the surface snow.  There have been reports of skier triggered wind slabs that were between 1 to 2 feet deep on cross-loaded slopes. Avoid wind loaded slopes.

The second avalanche problem is loose dry releases.  The new snow is light, low-density and did not form a cohesive slab.  Look for large sluffs to be triggered easily today.  These should not be a problem to manage unless they knock you off your machine or down and carry you into a terrain trap.

The final avalanche concern is persistent slabs.  Our buried surface hoar on shadier aspects and crusts on more sun exposed slopes, still need a pit dug to see if they are reactive. Before committing to a steep slope, dig a pit 3 feet down and identify any layers of concern, and see if they are reactive in stability tests.

Overall our snowpack is strengthening.  There are weak layers in our snowpack; they are becoming less reactive with time.  Identify wind loaded terrain and avoid it.

Avalanche and Weather Outlook

We are entering a warm up with potential to see rain fall on a dry snowpack. See the forecast here. With the addition of rain and warmer temperatures expect the avalanche danger to increase quickly.

I will issue the next advisory on Saturday,February 03, 2018

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-3

    Possible

    The likelihood of an avalanche resulting from this problem.

  • IMAGE

Look for rounded pillows of snow near ridgelines and on cross-loaded slopes. Recognize signs of instability such as cracking in the surface snow.  There have been reports of skier triggered wind slabs that were between 1 to 2 feet in depth on cross-loaded terrain. Avoid wind loaded slopes.

 

Problem 2 - Loose Dry

  • TYPE

    loose-dry

    Loose Dry

    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-4

    Possible/Likely

    The likelihood of an avalanche resulting from this problem.

The new snow is light, low density and did not form a cohesive slab.  Look for large sluffs to be triggered easily today.  These should not be a problem to manage unless they knock you off your machine or down and carry you into a terrain trap.

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-1

    Unlikely

    The likelihood of an avalanche resulting from this problem.

  • IMAGE

Our buried surface hoar on shadier aspects and crusts on southern aspects still need a pit dug to see if they are reactive. Before committing to a steep slope, dig a pit 3 feet down and identify any layers of concern, and see if they are reactive in stability tests.

VIDEO

Central Bitterroot 01/21/2018

GALLERY

Twin Lakes-31-Jan
Twin Lakes-31-Jan
Twin Lakes Pit
Twin Lakes Pit
Slide path 1/31/18
Slide path 1/31/18
Deep New Snow
Deep New Snow
Wind loaded slope
Wind loaded slope

Observations 01/31/2018

FORECAST & OUTLOOK

We are entering a warm up with potential to see rain fall on a dry snowpack. See the forecast here. With the addition of rain and warmer temperatures expect the avalanche danger to increase quickly.

 

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.