THIS SNOWPACK SUMMARY EXPIRED ON January 9, 2015 @ 10:25 pmSnowpack Summary published on January 9, 2015 @ 5:25 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.
The Sunday afternoon to Monday morning massive storm has modified greatly with 48 hours of above freezing temperatures. That potential "top five powder day" is now capped with a melt-freeze crust at all elevations. Below that crust is snow that has consolidated to form a 1 finger hard slab. Midway through the new storm slab is a weak layer of near surface facets that fail with moderate force. With the forecast for below freezing temperatures and no storm or wind loading, we expect snowpack conditions to improve as cold temperatures are driven deeper into the snowpack.
Avalanche Character 2: Deep Slab
Deep Slab avalanches are destructive and deadly events that can release months after the weak layer was buried. They are scarce compared to Storm or Wind Slab avalanches. Their cycles include fewer avalanches and occur over a larger region. You can triggered them from well down in the avalanche path, and after dozens of tracks have crossed the slope. Avoid the terrain identified in the forecast and give yourself a wide safety buffer to address the uncertainty.
We continue to halt our snowpack investigations when we did down to the benchmark Thanksgiving rain crust. This crust is penetrated only with stiffest and sharpest of shovels.
We will continue to monitor this deep slab for changes as the season progresses. However, we expect this condition to persist well into the winter season.
Massive storm loading followed by several days of above freezing temperatures results in some very interesting snowpack evaluations. Our overall hazard assessment has improved since Tuesday's advisory. The forecasted weather leads us to believe that snowpack conditions will continue to improve slowly. Dangerous avalanche conditions still persist out there and back country travelers need to continue to exercise their best evaluations of snowpack, terrain, and route finding.
Today I visited Poorman Basin in the East Cabinet Range. Upslope of the Snotel site on a southerly aspect at 5500 feet elevation I encountered 55 inches of snowpack. Five inches of snowpack settlement had occured at this Snotel site since Tuesday morning. I encountered no evidence of wind transport during my travels. The top three inches of the snowpack is a pencil hard tempearture crust. It is supportive of skis and snowmobile except during aggressive manuvering. The next 14 inches is a one finger hard slab. Below this is a six inch pencil hard slab over a two inch knife hard rain crust. Finally, a six inch pencil hard slab sits on the Thanksgiving rain crust. I did NOT investigate below the Thanksgiving rain crust as it has been impenetrable since being formed. The Extended Column Test yielded partial propagation (propagation line visible at mid photo) at the 46 inch level with moderate force. Failure was on a very thin layer of small (1mm) near surface facets.
Weather and CURRENT CONDITIONS
Since Tuesday, January 6th weather in the Kootenai Region has been warm and dry. All Snotel sites reported above freezing temperatures until Thursday afternoon. Since then temperatures are on a slow slide downward. No sites recorded any measureable precipitation Tuesday morning. All sites recorded 2 -5 inches of snowpack settlement with the above freezing temperatures. There is little evidence of wind transport in our ranges. Today's weather in the Poorman Basin of the East Cabinet Range brought light snow, calm winds, and 25º F with a cooling trend. Forecasted weather for the Kootenai region is mostly cloudy with continued cooling through Friday. Thereafter, temperatures will start to warm but not to above freezing. Winds will start out of the east Thursday, then switch to the southwest by Friday afternoon. Winds are not forecasted to transport snow. There is a 30% chance for a trace of snow Saturday.
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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