Posted:
Jan 24, 2017 @ 6:30 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 24, 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 11 F to 18 F in the region. Winds are 8 mph with gust of 13 mph out of the NNE in the Bitterroot.  Point Six, in the northern part of the advisory area, winds are reading 9 mph with gusts of 13 mph out of the E.  The forecast area received 0 to 2 inches of new snow in the last 24 hours.  The new snow had SWE’s ranging from 0 to .2 inches of water.

Tim and I took sleds to Granite Pass in the northern Bitterroot, yesterday.  Matt and Josh were in the Rattlesnake over the weekend, teaching a level 1 class.  All of us observed fresh shallow wind slabs. We saw no propagation in ECT’s.

Today’s primary avalanche problem is small, shallow wind slabs.  These slabs are 1 to 2 inches in depth. They are isolated on leeward terrain.  Wind slabs can be identified by smooth rounded pillows on the surface near ridgelines.

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.  These instabilities are healing, and we have not seen propagation in tests for almost two weeks. Still, dig a pit before committing to any steep slopes.

Avalanche and Weather Outlook

A subtle disturbance is moving through the region today through Wednesday; this will bring a couple of inches of snow to the area.  With these conditions, the avalanche danger will stay the same.

Join us tonight at the University of Montana in the North Urey Lecture Hall at 6:00 pm for a free lecture on Introduction to Avalanches.

If you are out in the backcountry, please send us your observations, these are very helpful in producing the advisory.  I will issue the next advisory on January 26, 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.

  • IMAGE

Shallow wind slabs in isolated pockets.

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-1

    Unlikely

    The likelihood of an avalanche resulting from this problem.

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

Granite Pass 01/23/2017

GALLERY

Lolo Pass-23-Jan
Lolo Pass-23-Jan
Rattlesnake 01_22_17
Rattlesnake 01_22_17
Granite Pass
Granite Pass
Wind Transport Point Six
Wind Transport Point Six
Rattlesnake Level 1
Rattlesnake Level 1

Observations 01/20-23/2017

FORECAST & OUTLOOK

A subtle disturbance is moving through the region today through Wednesday; this will bring a couple of inches to the area.  With these conditions, the avalanche danger will stay the same.

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.