Eastern Sierra Snowpack Summary - Mar 26 2016

THIS Snowpack Summary
EXPIRED ON March 28, 2016 @ 7:03 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center
Snowpack Summary

Avalanche concerns for Saturday thru Sunday: loose-wet instability primarily on steep mid-elevation solar aspects (SE-S-SW-W) as they heat up and soften throughout the day. Secondary concern is small isolated pockets of sensitive wind slabs on upper elevations steep exposed slopes with a focus on N-NE-E-SE facing aspects.

Forecasted clear skies, moderately warm temperatures, and light winds into early Sunday will make loose-wet instability a possibility on solar aspects as they warm throughout the day. This may be encountered on easterly facing slopes in the late morning, southerly facing slopes midday, and westerly facing slopes by the afternoon.  Upper elevation temperatures will remain cool, confining wet-loose activity to mid elevation slopes (~ 11,000’) and lower. Cool nighttime temperatures will allow for a strong refreeze of solar aspects and lower elevation northerly aspects where snow is present.  If you will be traveling in avalanche terrain, plan to be off mid-elevation solar aspects and generally low elevations slopes prior to them showing signs of instability such as boot penetration beyond boot-top or new rollerball activity.

The new wind deposits and wind slabs that formed earlier in the week are showing signs of settling and stabilizing. The wind slabs are generally 8”-10” in depth and confined to the upper elevations in the Mammoth basin, tapering off to 4”-6” north and south, dramatically less south of Rock Creek. Winds predominated out of the SW during this storm, but switched around from the north for a period on Tuesday afternoon evening, resulting in wind deposits on a variety of aspects. Light to breezy SW winds over ridge tops persisted over the past couple of days, which could form small sensitive wind slabs prone to triggering. Sunday SW winds are forecasted to increase through the day and form new wind slabs primarily on steep exposed high elevation slopes just below ridgelines, and on the sidewalls of gullies, primarilly on NW-N-NE-E-SE aspects. Be on the lookout for hollow sounding dense snow and assess slab sensitivity. Remember, small avalanche can carry a skier or boarder into steep rocky terrain and result in injury.   

Additional hazard considerations: very firm melt-freeze crusts and wind board conditions exists (slide-for-life) throughout much of the region’s mid to upper elevations. Realize that a fall maybe very hard to self-arrest. Be prepared for these conditions: crampons and ice axes are recommended, and be well practiced in self-arrest. 

weather

Sat: A weak short wave ridge is expected Saturday with light winds and temps a little above average.

Sun-Monday: winds are expected to increase during the afternoon ahead of a cold front expected to skirt northern California Monday morning with precip staying predominately north of I-80 and U.S. 50. Gusts of 30-35 mph are possible for much of the area Sunday afternoon and evening. Monday, behind the front, it will be much colder with scattered snow showers in the afternoon.

Tuesday: Unseasonably cool and unstable conditions will persist Tuesday underneath upper Low situated across the Great Basin. Scattered snow showers will develop early in the day with an isolated thunderstorm is not out of the question. Models continue to show a building upper ridge into the Pacific Northwest within a larger scale blocking pattern near the west coast later in the week.

recent observations

Bardini Canyon, Table Mountain (3/24/16) booting up fairly straightforward with good snow support. A tongue of snow comes down to about 300 yards from Four Jeffries, so approach and walk-back through sagebrush is currently short. Mostly good corn, though crusting a bit late afternoon. Coverage is good on left side (facing uphill) in lower canyon and there is still good snow coverage atop Table Mountain. Observed some minor rollerball activity on a steep and sunny slope, and settled slab exhibited an old two-inch break at the very bottom of the "tongue".

Esha (3/24/16)

Highly wind-affected snow on the north face of Esha yielded everything from boilerplate ice to hard Sastrugi to perfect corn to blown-in powder above 10,500 ft. Blowing snow at the summit, old roller-balls visible on SE aspects

Nevahbe Ridge (3/23/16) - Hard freeze evident overnight. Some light active snow transport along the Nevahbe Ridge and the upper reaches of Mt. Morgan North. Snow surface - melt freeze/very firm in the bottom portion of the gully, cold dry snow in the lowest throat over wind board, which was a semi-supportable. Small, isolated wind slabs 3-6" thick, noted. These failed in hand shear tests with moderate force Q3, at the melt freeze crust below. Skiing was better than we expected with the crust more supportive than expected and thicker wind affected snow easily avoided. No cracking or whumphing observed during our descent. Ski cuts above tracks did not initiate failure in the "slab" between. Snow surface on the apron of the gully or on our return to the car softened very little.

Onion Valley, Mt Gould/East Face (3/23/16) - Rd is clear to the trailhead. 11,600', 10am - Some softening / moist snow at surface at, South facing slope. Boot penetration very minimal, crampons necessary. 11,200', 2:30pm - Very minimal softening of east and southeast slopes above. 10,500 - 9,200', 3:00pm -aspects with southerly exposure had good surface softening yet remained very supportable (good corn).  Evidence of new snow and wind transport from Monday night (1-3cm down low, up high some areas of 2-5"). No evidence of: instabilities, wind slabs, rollerballs, or loose-wet activity.  Some evidence of limited isolated rollerball activity noted from several days ago below 10,500'.  

 

Avalanche Problem 1:   Loose Wet
  • Type

The new wind deposits and wind slabs that formed earlier in the week are showing signs of settling and stabilizing. The wind slabs are generally 8”-10” in depth and confined to the upper elevations in the Mammoth basin, tapering off to 4”-6” north and south, dramatically less south of Rock Creek. Winds predominated out of the SW during this storm, but switched around from the north for a period on Tuesday afternoon evening, resulting in wind deposits on a variety of aspects. Light to breezy SW winds over ridge tops persisted over the past couple of days, which could form small sensitive wind slabs prone to triggering. Sunday SW winds are forecasted to increase through the day and form new wind slabs primarily on steep exposed high elevation slopes just below ridgelines, and on the sidewalls of gullies, primarilly on NW-N-NE-E-SE aspects. Be on the lookout for hollow sounding dense snow and assess slab sensitivity. Remember, small avalanche can carry a skier or boarder into steep rocky terrain and result in injury.  

 

Avalanche Problem 2:   Wind Slab
  • Type

Light to breezy SW winds over ridge tops persisted over the past couple of days, which could form small sensitive wind slabs prone to triggering. These may be found on steep exposed high elevation slopes just below ridgelines, and on the sidewalls of gullies.  Be on the lookout for hollow sounding dense snow and assess slab sensitivity. Remember, small avalanche can carry a skier or boarder into steep rocky terrain and result in injury.   

Two-Day Mountain Weather Forecast  Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Saturday Saturday Night Sunday
Weather: SUNNY CLEAR THEN BECOMING PARTLY CLOUDY PARTLY CLOUDY
Temperatures: 45 TO 55 deg. F. 22 TO 29 deg. F. 44 TO 54 deg. F.
Wind direction: NORTHEAST LIGHT WINDS BECOMING SOUTHWEST SOUTHWEST
Wind speed: 10 TO 15 MPH. GUSTS UP TO 25 MPH IN THE MORNING 10 TO 15 MPH AFTER MIDNIGHT 10 TO 15 MPH INCREASING TO 25 TO 30 MPH WITH GUSTS TO 45 MPH IN THE AFTERNOON
Expected snowfall: 0 in. 0 in. 0 in.
For above 10000 ft.
  Saturday Saturday Night Sunday
Weather: SUNNY CLEAR THEN BECOMING PARTLY CLOUDY PARTLY CLOUDY
Temperatures: 35 TO 45 deg. F. 20 TO 28 deg. F. 33 TO 43 deg. F.
Wind direction: NORTHWEST SOUTHWEST WEST TO SOUTHWEST
Wind speed: 15 TO 20 MPH WITH GUSTS TO 30 MPH 10 TO 15 MPH 10 TO 15 MPH WITH GUSTS TO 25 MPH, INCREASING TO 25 TO 30 MPH WITH GUSTS TO 45 MPH IN THE AFTERNOON
Expected snowfall: 0 in. 0 in. 0 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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