Wet snow instabilities and deep persistent weaknesses may be possible to trigger on steep terrain (37 degrees or steeper) and isolated features. Normal safe travel precautions are advised.
The Bottom Line: Wet snow instabilities have been increasing in the afternoon due to daytime warming, sun exposure, and light winds (less of a factor today with moderate winds cooling the snow surface and on Saturday with the incoming cold front). Utilize safe travel precautions for the possibility of afternoon wet avalanches in wind-protected areas on Friday. Lingering deep slab instabilities persist on some northerly aspects, though they are hard to trigger. Watch for isolated pockets of deep slab instabilities on steep (37 degrees or steeper), rocky terrain on shaded / northerly aspects and evaluate terrain configuration carefully.
Discussion: Very warm daytime temps and clear nights over the past week have perpetuated the February melt/freeze cycle. Surface snow has been moist to wet in the afternoons and corn skiing has generally been good. Yesterday I observed debris from a wet loose avalanche in the Upper McKay Creek drainage, though from a distance it was hard to determine its size class. Lower elevation southerly aspects have lost much of their snowpack, resulting in bare ground over wide areas. Highway 108 and Leavitt Lake Road in the BWRA have long stretches of pavement/dirt/mud. Upper mountain cirques are still holding snow - snowpits have been ranging between 50cm and 100cm in depth. Northerly aspects are still showing near-surface faceting and persistent weaknesses deeper in the snowpack.
I did a crown profile yesterday on a northerly aspect at 9,100' where wet slabs from the Feb 6-9 storm event had released. Interestingly, I saw two propagating fractures in separate faceted layers - neither of which failed during the storm loading or when the wet slab avalanches ran over them. The failures were hard to trigger - shoulder hits (ECTP24) for both fractures. These results, combined with two similar reports from observers over the past week, suggest lingering deep slab instabilities persist on isolated terrain features - shaded, northerly aspects where well-developed facet layers exist. No slab avalanches have been observed in the BWRA since the storm-related avalanche cycle two weeks ago.
Other snowpits and column tests above treeline have not revealed any propagating fractures in the past week. Some roller-ball activity and small wet-loose avalanches have been observed in the last few days in the BWRA. Side-slipping on skis through moist/wet surface snow overlying hard melt/freeze crust has not produced any momentum-building wet loose slides.
Friday will remain warm with moderate winds to cool the snow surface. A cold front from Canada pushes down the Eastern Sierra Front Saturday into early next week, dramatically reducing temperatures and bringing a chance of precip. Mixed rain/snow, then snow even at lower elevations, will favor the Eastern Sierra south of I80 and in Mono County, though accumulation is expected to be light. Temps are expected to rise again by mid next week and weather should remain warm and dry for the rest of the week.
This snowpack summary applies only to backcountry areas in the Bridgeport Winter Recreation Area. "http://bridgeportavalanchecenter.org/forecast-area-map" Click here for a map of the area. This snowpack summary describes general avalanche conditions and local variations always occur. This snowpack summary expires in 48 hours unless otherwise noted. The information in this snowpack summary is provided by the USDA Forest Service who is solely responsible for its content.
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