Posted:
Dec 12, 2016 @ 8:30 am

Good morning, this is Travis Craft with an early season snowpack and avalanche update.

Weather and Snowpack

Mountain temperatures are 12 F to 24 F this morning.  In the northern part of the advisory area winds are 17 mph out of the west with gusts of 27 mph.  The southern area winds are coming out of the WSW at 6 mph with gusts of 10 mph.  Snotels are reporting 5 to 12 new inches of snow in the last 24 hours.

This new loading on top of the existing poor structure of our snowpack will make it very reactive.  In the last 48 hours we have had reports of natural avalanches near St. Mary’s peak and a slide triggered on Little St Joe in the Bitterroot.  Also, a public observation from the Rattlesnake showing instabilities.  The snowpack needs some time to adjust to the new snow.  With more loading from snow and wind on the poor structure of the snowpack we will see the avalanche danger rise.  I would be very cautious traveling in avalanche terrain and make very conservative decisions.

We will issue our first advisory with an adjatiave rating on Thursday, December 15 2016.

We have many upcoming events check our education page for listings. Also if you are out recreating in the backcountry, please send us your observations these are very helpful in producing the advisory.

Ski and ride safe.

 

READ FULL ADVISORY  

Problem 1 - Persistent Slab

  • 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-4

    Possible/Likely

    The likelihood of an avalanche resulting from this problem.

Facets are reactive in tests and have been triggered by skiers.

Problem 2 - Wind Slab

  • 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-4

    Possible/Likely

    The likelihood of an avalanche resulting from this problem.

Lots of new snow with strong winds have loaded up leeward slopes.

FORECAST & OUTLOOK

 

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.