Dec 1, 2010 @ 2:41 pm

December 1, 2010 Update

Hello!  It’s December 1, 2010 and this is Steve Karkanen with early season avalanche information from the West Central Montana Avalanche Center in Missoula. 

The Thanksgiving holiday will be remembered for a long time for the epic snow conditions at local ski resorts and in the backcountry.  Most mountain locations now have more than enough snow to recreate on as well as the potential for avalanche activity on steep terrain.

Our regular avalanche advisories start on December 17 but we will post information updates as conditions change and we receive good information.

This winter is shaping up to be a good one for snow depth stability.  The heavy dense early storms laid down a solid base and subsequent snowfall is bonding well to the earlier layers.  Nearly all of the reports we have received so far indicate a mostly stable condition with a few exceptions.  We received a report of unstable conditions from a party on St Mary’s Peak in the Bitterroot.  They reported that high winds scoured the southeast aspects and they observed cracking and whumpfing on their hike.

The snowpack has now had several days at moderate temperatures and is adjusting well to last weekend’s storm.  The Weather Service is forecasting several inches of new snow by the weekend so the primary concern will be how well the new snow bonds to the older snow and how heavily the wind loads steep leeward terrain. 

Remember that most avalanches occur during or immediately after a storm and that if you see signs of avalanche activity or any of the below indicators, the snowpack is probably unstable.

The major red flags or indicators of an unstable snowpack condition are:

  • Recent avalanche activity – this is the clearest indicator of an unstable snowpack that many people overlook.
  • Heavy new snowfall or rain – most avalanches happen during or immediately after a storm
  • Collapse noise or a whumpfing sound of the snow – if you experience this on flat terrain assume unstable conditions on a steeper slope.
  • Shooting cracks or fracture propagations running out from you as you travel, typically associated with collapse noise.
  • High winds – any amount of snow with wind can quickly raise the avalanche danger on leeward terrain.
  • Warming temperatures – a storm that starts out cold and turns warm puts heavy snow on cooler weaker layers.

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.