Dec 27, 2011 @ 6:23 am

December 27, 2011 Avalanche Advisory


On slopes  above 5000 feet that are steeper than 35 degrees and wind-loaded there is a Considerable Avalanche Danger. On all slopes above 5000 feet that are steeper than 35 degrees there is a Moderate Avalanche Danger

Good morning, this is Dudley Improta with the West Central Montana Avalanche Center’s advisory for December 27, 2011

Weather and Snowpack Analysis

Over the past couple of days the region received anywhere from 2 to 4 inches of snow and it is snowing lightly this morning in the northern part of the advisory area and along the Idaho border. This new snow is sitting on surface hoar produced from the brief clearing on Saturday night. The new snow is very weak; sluffing easily when skied and failing with very low scores in stability tests. This new layer may be a problem in the immediate future and the surface hoar layer from mid-December is a problem right now.

We went back into the Rattlesnakes yesterday, since we called high avalanche danger in there on Friday. We looked at numerous exposures and did a bit of digging. That weak layer we talked about Friday (this video is still pertinent) is now 18 inches from the surface; and it is still failing and propagating with stability tests. That’s 18 inches from the surface in the Rattlesnakes; in the rest of the advisory area there is 6 to 12 inches of snow sitting on this layer.  On the tour we had some collapsing of the snowpack but did not see recent avalanching.

The wind has been moving snow. East and north aspects are loaded, particularly above 6000 feet. These are the aspects I would pay very close attention to. This photo shows what the wind has been doing the last few days.

Weather Forecast and Avalanche Outlook

The Weather Service is predicting a series of storms this week – beginning tonight – which may bring a foot or more of heavy wet snow to many mountain locations. These storms will be accompanied by strong winds. This predicted snow will test the weak layers in the snow pack (the surface hoar from Saturday and the mid-December weakness) and we are likely to see high avalanche danger – as happened in the Rattlesnakes – throughout the advisory area. Snow is expected at 5000 feet and above with strong possibilities of rain below that. Either way, rain or wet snow will increase the avalanche danger.

For those interested in looking at snow profiles from this season we are posting them in a folder of 2012 snow profiles in our photo section also.

Steve will issue the next advisory Friday, December 30.

You might have wished for snow for Christmas, looks like it worked out. Ski and ride safe!

If you get out and see avalanche activity or want to send us quick snow observations please use our public observations form on the home page or write us at [email protected] with any observations or questions.



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.