THIS SNOWPACK SUMMARY EXPIRED ON March 4, 2015 @ 5:55 am
Snowpack Summary published on March 3, 2015 @ 5:55 am
Issued by Ben Bernall - Kootenai National Forest
Avalanche Character 1: 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.

This mid pack persistent slab is found wherever we dig pits in our region.  Time, temperature, and gravity created a very strong surface layer that makes it difficult to impact the mid-pack weakness. Even though this weak layer requires considerable force to fail, we still continue to observe full propagation across the column of this failure.  The failure layer is 2-4 mm faceted crystals.

 

Snowpack Discussion

Snowpack conditions are largely stable with very hard near surface crusts making it difficult to impact mid pack weaknesses.  There are no significant storm loading, wind transport, or thawing events in our weather forecast through Wednesday.  Extended forecasts call for dry weather and near normal tempertaures (melt-freeze cycles) through the weekend.

This has been a very difficult February for winter enthusiasts.  The hydrologic graphs for 2015 are tracking in mirror image of 2005. If it does indeed mimic 2005, then significant winter weather will arrive in early April after everyone has given up hope for powder days.  Really, can it get any worse?  We can reasonably expect our next significant weather event to be thawing conditions.  But for now, backcountry travelers should identify thin snowpack areas and avoid the weaknesses associated with them.  In the Kootenai Region under our current snowpack, that is a lot of area to be examining and evaluating.  

recent observations

Yesterday, I visited Lost Horse Mountain (6,559 feet) in the Purcell Range (27 air miles north of Libby). There I encountered a 31 inch deep snowpack on a steep east aspect. The top inch was new snow over night. The next 8 inches was multiple knife hard ice layers tightly bonded together. Penetration of this layer was very difficult with an avalanche shovel. Below this is a 4 inch pencil hard layer that sits atop a 1 inch knife hard ice crust.  Below these layers is a 5 inch thick four finger soft layer composed of 2-4 mm weak snow (facets). Below this is a 5 inch thick 1 finger hard slab. Finally, a 7 inch knife hard crust rests on the ground.

Extended Column Tests required hard force but produced full propagation between the 1 inch ice crust and the 4 finger soft layer (ECTP 27, Q1). A 14 inch hard slab sits above this layer

 ECTP 27, Q1 on a soft faceted layer

 Pit cards define the 4 finger soft facet layer

weather

Since the Thursday February 26th advisory, weather in the Kootenai Region has been cold and dry. All SNOTEL sites have been reporting below freezing tempeartures day and night, with single digits Saturday morning. SNOTEL sites are reporting SWE increases of 0.1 - 0.3 inches since Thursday afternoon. Weather yesterday at Lost Horse Mountain (6,559 feet) was low clouds creating limited visibility, light snow with an accumulation of 1 inch, tempearture of 25º F, and east winds at 3-5 mph.  Forecasted weather through Wednesday calls for decreasing cloud cover, cold temperatures with a gradual warming by Wednesday (25-30º F). Snow ended Monday night with total accumulations of 2-4 inches, and northeast winds at 18 mph Monday night decreasing to 5 mph out of the southwest by Wednesday. 

Disclaimer

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.