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Rollerballs and Deep Slab Hunting
Location Name:
BNSF Avalanche Safety - Running Rabbit Mtn GNP
Observation date:
Friday, January 24, 2020 - 17:15
Is this an Avalanche Observation:
Yes
Observation made by:
Public
Tabs
Quick Observation
Toured up the Shed 10.7 ridge on the south face of Running Rabbit Mtn. After checking on the Shed 11 weather station, continued up the SW ridge of Running Rabbit to 7200 feet and checked on the uppermost starting zone of Path 1163. Descended the same route.
Objectives were to observe recent avalanche activity and new snow depths and wind-loading above the rain/snow line. Also wanted to seek out some steep, rocky, high elevation terrain with shallow snowpack depths and assess the snowpack structure/stability at a location representative of a possible deep persistent slab trigger point.
Rollerballs were widespread on slopes steeper than 30° and below 6000 feet, but only a few progressed to wet loose avalanches. The few wet loose avalanches observed were small D1-D1.5.
No slab avalanche activity observed.
No collapsing or audible failures during the tour.
Ski cuts on small test slopes did not produce any cracking or slab releases. But below 6000 feet they set off plenty of nice sized rollerballs but without any wet loose avalanches.
No wind-loading due to a fully wet snowpack surface up to about 6500 feet. Above this elevation a slightly moist snowpack surface up to 7000 feet combined with an actively forming rime crust acted to limit blowing and drifting snow.
The recent (MLK) rain crust was only about ¼ thick and present from the Canyon floor up to 6500 feet where it thinned and disappeared. There was 4-5 inches of snow on top of the crust around 6000 feet.
Dug a snowpit and conducted a full profile on the ridge immediately west of the upper starting zone of Path 1163, 7200 feet, easterly aspect, 28° slope (pit profile below).
Snow depth here was only about 40 inches and the November crust/facet layer was present at the base about 30 inches down.
The holiday crust was not present at this location which is consistent from earlier observations.
The first Extended Column test yielded ECTP16 on the basal facets and the column quickly slid into the pit. The second ECT yielded ECTP16 on the same layer.
Very light rain with temperatures in the mid-30s to 40 °F from the Canyon floor up to 5500 feet with calm to light SW winds.
Very light rain/snow mix from 5500 to about 6500 feet with light SW winds.
Occasional very light (S-1) snowfall with temperatures just below freezing and light SW winds from 6500-7200 feet.
Skies were mostly cloudy with occasional breaks revealing some blue sky.
Snowpack, Avalanche, Weather Images:
