THIS SNOWPACK SUMMARY EXPIRED ON March 13, 2015 @ 10:03 pmSnowpack Summary published on March 13, 2015 @ 5:03 am
Issued by
Ben Bernall - Kootenai National Forest
Avalanche Character 1: Loose Wet
Loose Wet avalanches occur when water is running through the snowpack, and release at or below the trigger point. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
With no freezing temperatures since Monday AM and periodic light rains adding free water to the snowpack, our top layers (16 inches) are very loose. In travelling to the site, the snowmobile would lurch from side to side as a ski penetrated. With very cautious riding, you could achieve a level ride most of the time. The loose wet snowpack condition is forecasted to persist through Saturday. Saturday's forecasted significant (0.39 Inch) rain on snow will further degrade snowpack stability.
Backcounrty travelers should avoid over steep slopes especially on Saturday during the rain on snow event. Risk will increase significantly if forecasted amounts of rain are delivered.
Snowpack Discussion
Back country travel on our current meager snowpack is really difficult. Last Monday, I attempted unsuccessfully to access four sites to dig for snowpack information. Today I made a north aspect approach to the highest peak (Mount Henry 7,243 feet) in the Purcell Range and was turned back after 4 miles of travel. I was fortunate today to have a nearby site with a north aspect approach that allowed 12 miles of travel on mostly complete snowpack. With no refreeze since Monday AM and none forecasted through Saturday, back country travelers need to be cautious on steeper slopes, especially with terrain traps below them. If it starts raining during your trip, best advice is to immediately return to the trailhead via the safest route. Avalanche hazard normally rises significantly during heavy rain on snow events. Do not ignore the obvious signs - be safe out there.
recent observations
Yesterday I visited Boulder Pass (6,000 feet) in the Purcell Range, 31 air miles north of Libby. There, I encountered a 37 inch snowpack on a steep north aspect. The top 4 inches was 4 finger soft and wet from recent rains. Below that is a 12 inch layer that is 4 finger to fist very soft and mostly dry. These layers sit atop an 11 inch knife hard crust. The bottom 10 inches of the snowpack is loosely consolidated large grains. Recent rains and above freezing temperatures since Monday AM have had great influence on the top 16 inches of the snowpack. Snowmobile and ski penetration are 4 and 6 inches respectively, and boot penetration is 10-12 inches. Extended Column Tests produced one fracture with hard force (ECTN30) 16 inches from the surface. No propagation of this failure was observed.
(Boulder Pass east of Mt Henry)
(Bould Pass pit ECTN30)
Weather and CURRENT CONDITIONS
weather summary
Since the Tuesday, March 10th advisory, weather in the Kootenai Region has been warm and wet. All SNOTEL sites are reported above freezing temperatures since Monday AM. Day time highs range from mid to upper 40's F. SNOTEL sites are reported snowpack settlement of 2 - 4 inches, and SWE increases of 0.2 - 0.4 inches after several periods of light rain. Weather yesterday east of Mount Henry (7,243 feet) in Boulder Pass was mostly cloudy, 35º F, southwest winds 5-7 mph, with light rain overnight. Forecasted weather through Saturday calls for partial clearing Friday followed by cloudy conditions Saturday. Temperatures will stay above freezing with day time highs in the mid 40's F to low 50's F. Chance of precipitation is 100% Saturday in the form of rain with 0.39 inch possible.
(Mt Henry 7,243' shrouded in clouds)
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.
