Posted:
Dec 5, 2016 @ 7:39 am

Good Morning, this is Logan King with an early season conditions update.

A significant storm has rolled into West Central Montana bringing cool temps, wind and snow. The storm system started working its way into the region early Sunday and has since dropped 4-12 inches of snow at mountain locations across the advisory area. The new snow; as enticing as it may be warrants some close attention.

Primarily the new snow will require some time to settle. Thats right, the ground counts as a bed surface and the snow will require time to bond to the ground in areas where little or no snow had fallen. At higher elevations and some cold northern aspects where thin snowpacks have existed prior to the new snows arrival, look for a weak basal facet layer that likely developed during cold nights in the shallow snowpack. The storm also came in with some wind, Point 6 shows winds peaking at 40+mph midday Sunday and are sustained at 20-30mph this morning. With new snow available for transport and noteworthy winds, keep an eye out for areas where windslabs and pockets of wind affected snow may be lurking.

This is the time of year to get your head on right, take your time and don’t rush into potentially dangerous situations. Take a class or re-read your favorite avalanche book. We have been hearing a few reports regarding conditions and will be starting regular avalanche advisories next week, so as always if you do venture out please share what you find through our public observation page.

READ FULL ADVISORY  

Problem 1 - Storm 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.

 

Problem 2 - 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-3

    Possible

    The likelihood of an avalanche resulting from this problem.

 

Problem 3 - Basal Facets

  • 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-3

    Possible

    The likelihood of an avalanche resulting from this problem.

 

VIDEO

12/05/2016 Lolo Pass

FORECAST & OUTLOOK

More snow is expected as another system will move through the region later this week.

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.