THIS SNOWPACK SUMMARY EXPIRED ON January 1, 2016 @ 3:43 pmSnowpack Summary published on December 31, 2015 @ 3:43 pm
Issued by Ben Bernall - Kootenai National Forest
Avalanche Character 1: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.
Snow stability tests today showed that the snowpack is indeed getting stronger. Test failures were either non-existent or failed under hard force with no propagation in Extended Column Tests. The primary concern with the snowpack in both the East and West Cabinets is found in isolated areas where ridge-top winds formed cohesive layers that are bonded poorly to old snow interface. This layer does not seem to be prominent or widespread but it is out there on isolated terrain features. Pay attention to these spots and be alert to "pillow" shaped apearances within the snow at or below ridgelines. It is likely these slides would be relatively small in size but should be given special attention in areas where a small slide has high consequences such as cliffs or trees lurking below.
Avalanche Character 2: Persistent Slab
Persistent Slab avalanches can be triggered days to weeks after the last storm. They often propagate across and beyond terrain features that would otherwise confine Wind and Storm Slab avalanches. In some cases they can be triggered remotely, from low-angle terrain or adjacent slopes. Give yourself a wide safety buffer to address the uncertainty.
The only failures in todays stability tests involved weak rounding facets between two rain crusts that failed approximately 4 feet below the surface with hard force. Triggering an avalanche on this layer within the East and West Cabinet ranges is unlikely at this point; however, this layer could still pose a hazard within the thinner snowpack of the Purcell range.
David Thompson Search and Rescue will be hosting an "Introduction to Avalanches" course on January 22nd and 23rd in Libby.
For specifics contact DTSAR Mountian Unit Leader Terry Crooks at 293-1618.
This past week I traveled into the Eastern Cabinets on December 27 and skied primarily on northerly aspects. Despite the nasty trail breaking conditions the snow felt good underfoot as we switch-backed our way up to the ridge. No cracking, collapsing or recent slide activity was observed. Confidence in the snowpack was increased even more as we dug in and performed both an extended column test and a compression test. Test results in the Extended column failed with hard force and no propagation was observed.
Today's travels took my partner and I to the Rattle Mountain area in the West Cabinets where we performed tests on both south and north aspects just below 6,000 feet in elevation. Once again, no "bullseye" information was observed in the form of cracking, collapsing or recent slide activity. None of the extended column tests produced a failure. The compression test results failed under hard force (CT28), failure occured on weak facets below the Deceber 9th rain crust. These facets appear to be rounding and the crust seems to be showing signs of decomposing as well. Though this layer is becoming less of a concern I will continue to watch it as the season goes on. Stay tuned.
The last observation of note today is the formation of surface hoar begining to grow on top of the snowpack. With the upcoming weather that is forecasted this layer is likely to grow in size. Though it is pretty to look at and fun to ski on it will likely cause problems down the road as it is buried by additional snowfall.
Weather and CURRENT CONDITIONS
The light steady snowfall, moderate temps and minimal wind have been favorable for improving the stability within the Kootenai N.F. snowpack. Stability tests and travel observations continue to show improvements in conditions with each venture into the mountains. The forecast for our region is showing plummeting temperatures, fog and valley inversions. This scenario will be very conducive to the creation and growth of surface hoar (feathery shaped crystals growing on the snow surface). This surface hoar could set us up for an increase in avalanche hazard as we exit this high pressure scenario and begin to recieve additional snowfall.
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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