Posted:
Jan 7, 2021 @ 6:18 am

The avalanche danger is moderate in the west central Montana backcountry today. Human triggered avalanches are possible today.

Good Morning. This is Travis Craft with the West Central Montana Avalanche Center advisory on Thursday, January 7th, 2021. This advisory is sponsored by the Trail Head. This advisory 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 22 degrees to 28 degrees F this morning. Winds are primarily calm, gusting to 12 mph out of the West. The forecast area has received 1 to 2 inches of new snow.

Warm temperatures yesterday produced roller balls and loose wet slides on sun-exposed slopes to 8000 ft. Pit tests showed that the snowpack is slowly healing and less reactive.

There are layers of concern in the top third of the snowpack and in the bottom third. Persistent weak layers are problems that stay with us for a long time. The structure of our snowpack should not be trusted. An unstable result in a pit test plays a large role in my decision-making process, and a stable result plays a small role.

Bottom Line

Choose simple terrain that does not expose you to terrain traps. Avoid likely trigger points on slopes. Dig a pit and look for stripes in the snow to identify weak layers. Perform a pit test to see how reactive these layers are. Choose a shallow spot to see if you have weak sugary snow at the bottom of the snowpack if you do choose another slope.Travel one at a time in avalanche terrain, carry a beacon, shovel, and probe. Remember to reassess conditions throughout the day and stay alert for signs of instability. Dig a pit. Look for red flags.

Upcoming Education Events:

Please visit our education page for an up to date list of regional educational events and course offerings. Below are a few select events and opportunities to check out.

Public Observations

Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. This forum is a great resource to glean information about current conditions. Here is the link to Public Observations.

Ski and ride safe.

READ FULL ADVISORY  

Problem 1 - Persistent Weak Layers

  • 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.

Faceted layers can be found throughout the forecast area. Shallower snowpacks have worse structure than deeper areas and are more suspect. In some places, persistent slabs are up to 40 inches thick and becoming low likelihood, high consequence problems. In other areas problem layers are in the upper foot of snowpack.

The problem facets tend to be concentrated around crusts. Look for these and soft sugary snow above and below as you assess the snowpack.

The extended column test (ECT) and the propagation saw test (PST) are best for assessing the stability of these layers.

Where facets are found stick to low angle slopes and avoid traveling under steep terrain as remotely triggered avalanches are possible

GALLERY

01_06_21_Central_Bitterroot
01_06_21_Central_Bitterroot
pin wheels
pin wheels
20210106_stmsrys
20210106_stmsrys
telemmadows
telemmadows
1_6_21_Central_Bitterroot_BSH
1_6_21_Central_Bitterroot_BSH

Observations 01/07/2020 Advisory

FORECAST & OUTLOOK

Light precipitation today with low accumulations of snow. Snow line will be around 4500 ft. See the forecast.

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.