Regional Weather and Avalanche Observations
LOCATION: Great Northern
REGION: Flathead National Forest
DATE: 12 Apr 2007
OBSERVER: Brad Lamson
GENERAL FIELD OBSERVATIONS:
AUDIBLE FAILUREYES
SNOWPACK COLLAPSINGYES
SHOOTING CRACKS IN SNOW SURFACEYES
WIND LOADINGYES
RECENT AVALANCHE ACTIVITYYES
RECENT SNOW FALLYES
RECENT RAIN FALLNO
SIGNIFICANT TEMPERATURE CHANGENO
AVALANCHE DEPOSIT ON ROAD OR RAILNO


AVALANCHE OBSERVATIONS:
AVALANCHE LOCATION: numerous
STARTING ZONE ELEVATION: 2000 m
SLOPE INCLINE: 30 degrees
ASPECT: NE
TYPE OF AVALANCHE: Hard Slab
AVALANCHE LIQUID WATER CONTENT:
AVALANCHE DEPOSIT LIQUID WATER CONTENT:
SIZE CLASSIFICATION:
Class 3-3.5 Could bury or destroy a car/ break a few trees.
TRIGGER: Walker
LOCATION OF STARTING ZONE: Top of Path
BED SURFACE: Crust
TERMINUS: Bottom of Runout Zone
FOR SHORT PATHS:

AVALANCHE DIMENSIONS
MINIMUM CROWN HEIGHT: 70 cm
MAXIMUM CROWN HEIGHT: 100 cm
WIDTH (FLANK TO FLANK): 300 m
TOTAL LENGTH OF RUN: 450 m
VERTICAL RELIEF: 350 m

OBSERVER NOTES:
Strolled up the Great Northern, the road is drivable for 11miles from the end of the pavement and then another 4 miles to the trailhead (used snowmachine). South and west aspect are fried but softened up later in the day, easy travel with supportable crust. Shaded areas still held powder snow. 20cm (avg) accumulation on these aspects overlying a hard crust. Once on the ridge, walked over to the east side to have a look and the whole thing blew. Several layers of storm accumulations went on a facet/crust layer, most like from early March. The slope at the top was 30' rolling over to 40'+, there was enough tension that it pulled snow from close to the ridge top. There were several other slides that had happened during Tues. storm and the crowns had partially filled in. Some of these slides were of the ridge tops and others were mid slope involving convex rolls and steep wind loaded deposits. Still lots of hang fire. Some huge cornices on the ridges also that have not broken off yet. We noted that this would be the kinda thing that you would slide into (30'), make 10 turns and then hit the convexity of the slope (40'), release all of the tension and when it went you wouold be right in the middle. We skied the west face back down before the sun/heat hit it, finding a line between some wet point release from the day before.
ATTATCHMENTS:

<< BACK TO INDEX