Eastern Sierra Snowpack Summary - Apr 09 2016

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THIS ADVISORY EXPIRED ON April 11, 2016 @ 7:39 am
Avalanche Advisory published on April 9, 2016 @ 7:39 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center
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.

Saturday: Loose Wet in the lower to mid elevations on all aspects due to weak overnight freezes and rain reported up to 10,000’ Friday night, which saturated the lower elevation snowpack and weakened the mid-elevation surface snow. Loose Wet avalanche issues are possible below ~9000’ on all aspects. Use extra caution on steep slopes 35 degrees and steeper, especially where terrain features can compound the consequences of small releases. 

Sunday: Temperatures are forecast to cool, which will permit the mid-elevations to freeze more thoroughly limiting the Loose Wet concerns for the mid-elevations to solar aspects as the new snow heats up during the day and has yet to bond firmly to the underlying snow. Lower elevations will continue to see weak freezes thru Sunday which will maintain the threat of Loose Wet releases on all aspects, possibly failing to ground. These slides may be small in size but can overtake a rider and possibly carrying them into hazardous terrain. 

Avalanche Character 2: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

Mid to Upper Elevations: As temperatures cool, the snowline is forecasted to descend with up to 7” possible by Sunday morning.  South to Southeast winds of 15 to 20 mph (Sat & Sat night) will possibly form sensitive wind slabs on SW-NW-NE-E aspects. Wind slabs may be found on leeward slopes, below ridgelines, around terrain features, or crossloaded gullies & depressions. Assess wind slab instability while ascending and prior to committing to big mountain faces with hazardous terrain. Quick hand pits can give you a good indication of how well fresh wind slabs are bonding to the adjacent snow interface. Additional concern is rider triggered sloughing in steeper terrain where the new snow hasn’t had sufficient time to form bonds to the underlying snow. 

 

Snowpack Discussion

Primary avalanche issues for Saturday will depend on elevation (~9000’ and below), loose wet avalanches on all aspects. From ~ 9000’ and above, isolated Wind Slabs on SW-NW-NE aspects. Sunday Loose Wet avalanches from ~8,500’ and lower. Above~8500’, possible wind slab formation on leeward slopes (SW-NW-NE-E aspects) deposited on melt freeze crust on solar aspects or on firm windpack found on northerly aspects in the mid to upper elevations. Either interface can slow bonding and act as a good bedsurface. As temperatures warm Sunday, Loose Wet releases maybe possible on solar aspects as the new snow heats up during the day and has yet to bond firmly to the underlying snow. 

Snowpack – The snowpack continues to transition toward spring with corn cycles setting up between spring snowfalls. At the mid and upper elevations, the snowpack consists of a relatively strong mid and upper snowpack with a snow surface of melt-freeze crust on solar aspects and firm windpack, wind board, with pockets of shallow soft snow on more northerly facing aspects. Lower elevations (~9,000’ and below), the snowpack is thinning quickly and consists of mostly granular melt/freeze snow. The storm system moving into the area this weekend has ushered in warm temperatures and rain up to the mid elevations with new snow in the upper elevations Friday night. As temperatures began to slowly cool Saturday, the snowline is forecast to slowly descending into the mid elevations. Lower elevation snow remains very warm with weak nightly freezes, trending toward isothermal. 

recent observations

Mt. Dade (4/7/16)-Overall cloud cover and low temps yielded firm crust throughout tour and most elevations, up in the basin at around 12000 ft began to see some colder pockets of cold snow and evidence of some ongoing wind transport of snow not glued down by melt/freeze. We bailed on the couloirs as it was bony and wind scoured with unappealing consequences. I took a couple turns the cut skiers right across apron over a small roll over, and triggered the slide from above as I traversed the leeward aspect of the roll. Crown was 10-12" with about 30ft width. Ran about 100 ft with fracture pattern. We did see some slab formation while skinning but no shooting crack or propagation. No other signs of instability seen. 

Dore Cliff Cirque, Lundy Canyon (4/6/16)- Toured up Dore Cliff cirque yesterday (4/6/16) and saw this avalanche across the canyon on a SE facing slope. Not sure if it was a windslab from our recent snow events but I'd guess it released due to rapid warming probably within the last few days. Also observed a small point release on a NE/E facing slope above Saddlebag Lake. No instabilities observed in the cirque I skied.

weather

Saturday: Low pressure west of the northern Baja continues to slowly move east towards the coast today with areas of light precipitation/showers increasing in coverage and spread northward. Snow levels are likely running between 8500 and 9000 feet. Tonight, the divergence band may rotate around into northeast CA and far northwest NV with favored areas receiving easily 0.25 to 0.50 inches of additional precipitation.
 
Sun-Monday: As the first upper low exits into Arizona, another disturbance dives into southern CA and the northern Baja. Residual moisture should allow at least some scattered showers late evening Sunday and in the morning Monday. 
 
Tuesday: Models continue to show inconsistencies in solution details but a wet unsettled pattern is forecast through much of next week. Tuesday, mild with only slight chance to low end chance pops.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Saturday Saturday Night Sunday
Weather: CLOUDY. SHOWERS. CLOUDY. SNOW SHOWERS IN THE EVENING...THEN CHANCE OF SHOWERS AFTER MIDNIGHT. CLOUDY THEN BECOMING MOSTLY CLOUDY. CHANCE OF SNOW SHOWERS IN THE MORNING...THEN SHOWERS LIKELY IN THE AFTERNOON.
Temperatures: 37 TO 47 deg. F. 29 TO 34 deg. F. 39 TO 49 deg. F.
Wind direction: SOUTHEAST SOUTHWEST LIGHT WINDS.
Wind speed: 10 TO 15 MPH WITH GUSTS TO 25 MPH. 10 TO 15 MPH WITH GUSTS TO 25 MPH IN THE EVENING BECOMING LIGHT.
Expected snowfall: UP TO 3 in. UP TO 2 in. UP TO 2 in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: CLOUDY. SNOW SHOWERS. CLOUDY. SNOW SHOWERS IN THE EVENING...THEN CHANCE OF SNOW SHOWERS AFTER MIDNIGHT. CLOUDY THEN BECOMING MOSTLY CLOUDY. CHANCE OF SNOW SHOWERS IN THE MORNING...THEN SNOW SHOWERS LIKELY IN THE AFTERNOON.
Temperatures: 30 TO 37 deg. F. 23 TO 29 deg. F. 32 TO 39 deg. F.
Wind direction: SOUTHEAST SOUTH LIGHT WINDS.
Wind speed: 15 TO 20 MPH WITH GUSTS TO 30 MPH. 15 TO 20 MPH WITH GUSTS TO 30 MPH SHIFTING TO THE NORTHEAST AFTER MIDNIGHT.
Expected snowfall: 2 TO 5 in. 1 TO 2 in. UP TO 2 in.
Disclaimer

This snowpack summary applies only to backcountry areas outside established ski area boundaries. This snowpack summary only describes general avalanche conditions and local variations always occur. This snowpack summary expires 24 hours after the posted time unless otherwise noted. The information in this snowpack summary is provided by the Eastern Sierra Avalanche Center who is solely responsible for its content.

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