THIS SNOWPACK SUMMARY EXPIRED ON December 10, 2014 @ 6:00 amSnowpack Summary published on December 9, 2014 @ 6:00 am
Issued by Ben Bernall - Kootenai National Forest
Avalanche Character 1: Storm Slab
Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.
Recent warm, wet weather has taken the loose dry snow of last week and modified it to form a soft slab. This soft slab sits atop a rock solid rain crust that formed after Thanksgiving. This soft slab reacts to pressure but fails to propagate at this time.
Travel on steep unanchored slopes of all aspects and all ranges in the Kootenai National Forest is not recommended. Crossing such slopes should employ normal precautions that includes traveling one at a time, using the same track, moving quickly, and spotting your partner from a safe location, etc.
Colder weather by the weekend should bring near normal tempertaures and possibly significant snowfall.
Today I visisted the east aspect of Flatiron Mountain 5891' in the Purcell Range. There I found 6" of modified new snow forming a soft slab. This sits atop our "benchmark" (Nov 27-28) rain crust which is quite supportable (see image #1).
Benchmark rain crust is between pit brush and phone card. The top three inches partially propagated in our Extended Column Test with easy force. The bottom three inches of the surface soft slab released with moderate force (see image #2).
Image shows partial propagation from left to right. The bottom 13 inches of the snowpack consists of a five inch raincrust "sandwich" that is mostly knife hard and an eight inch basal layer that is pencil hard. These fail only when hard force is applied in stability tests.
Attached image of a point release on an over steepened slope triggered by wet snow (see image #3).
Weather and CURRENT CONDITIONS
Mountain weather since Friday has been warm (>32F Friday AM through Sunday PM) in all ranges, and wet with the East/West Cabinet Ranges showing SWE increases of 0.9 inches. Much of the precipitation came as rain or snow showers. Weather today is dry with mountain fog to 6500 feet. E/SE winds are 3-5 mph and temperatures are just above freezing. Forecasted weather through Wednesday is mostly cloudy and above freezing during the day with light night time freezing. Winds from the SW at 6-10 mph with gusts 16-25 mph. However, there is very little snow available for transport. Light snow is forecasted only for the higher elevations (above 6500 feet).
This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.
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