Eastern Sierra Snowpack Summary - Mar 28 2016

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THIS ADVISORY EXPIRED ON March 31, 2016 @ 6:39 am
Avalanche Advisory published on March 28, 2016 @ 6:39 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center
Avalanche Character 1: 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.

Sunday/Monday’s recent shot of light snowfall, cool temperatures, and moderate Southwest winds have elevated the concern for new wind slabs that have likely formed in the mid to upper elevations on steep, exposed slopes, primarily on NW-N-E-SE facing aspects Monday but will expand to include W-S-SE by Tuesday as winds shift to the North – Northwest. Avoid freshly formed drifts below ridgelines, sidewalls of gullies and hollow sounding slabs. Remember, small avalanche can carry a skier or boarder into steep rocky terrain and result in injury.

Avalanche Character 2: 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.

Wednesday, as temperatures warm and rebound toward normal, the potential for loose-wet instability on solar aspects will rise as the slopes 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 relatively cool, confining most 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 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.

Additional hazard considerations: potential firm melt-freeze crusts and wind board conditions (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.

Snowpack Discussion

Primary avalanche concerns for Monday thru Wednesday: sensitive wind slabs in the mid to upper elevations steep exposed slopes with a focus on NW-N-E-SE facing aspects Monday but will expand to include W –S – SE as winds shift to the North – Northwest by Tuesday.  Secondary concern is for Loose-wet instability primarily on steep mid-elevation solar aspects (SE-S-SW-W) Wednesday as temperatures begin to rebound.

The snowpack is currently trending toward spring-like conditions with melt-freeze crusts forming at the surface between storms and the underlying snow beginning to turn towards corn on solar aspects in mid and upper elevations. Northerly aspects in the mid to upper elevations are still holding onto pockets of cold winter like snow but the aspect spectrum is narrowing to just North to Northeast aspects, favoring shaded and protected upper elevation slopes.

Sunday/Monday’s recent shot of light snowfall, cool temperatures, and moderate Southwest winds have elevated the concern for new wind slabs that have likely formed in the mid to upper elevations on steep, exposed slopes, primarily on NW-N-E-SE facing aspects Monday but will expand to include W-S-SE by Tuesday as winds shift to the North – Northwest.  Avoid freshly formed drifts below ridgelines, sidewalls of gullies and hollow sounding slabs. Remember, small avalanche can carry a skier or boarder into steep rocky terrain and result in injury

As Monday’s weak low eases east, temperatures will slowly rebound toward normal by Wednesday increasing the potential for loose-wet instability 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 relatively cool, confining most 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 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.

Additional hazard considerations:  potential firm melt-freeze crusts and wind board conditions (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.

recent observations

Sherwin Forest, Rock Chute (3/27/16):

- 1:00 pm, 10,000', ENE aspect, 33 deg slope: top 4 cm melted wet melt freeze crust, moist 8 cm down, boot penetration <10 cm. Breezy SW winds, moderate at ridgetop.  No snow transport visible anywhere. Clear skies. Some small rollerballs, nothing significant.  No new signs of loose-wet avalanche activity. Firm wintery snow upper 1/4 of Rock Chute, softer wintery snow bottom half. Variable below the Chute with: patches of nice wintery snow on northerly facing open slopes, to corn, to transitional moist snow.  Supportable throughout, even down low at 1:45 pm (although somewhat sticky skiing in lower 1/4 of elevation).

South Peak (3/26/16)

Headed for Olsen-South Peak saddle, then opted for lower portion of the right chute on South. Snow was stable, and the packed powder made for excellent skiing on these north-facing slopes. Snow sluffed from rocky sides made for crud in the upper chute, but nothing had propagated.  The avalanche path to the right (west) of the wide Olsen-South bowl appears significantly wind-loaded towards the bottom.

Esha Peak via Esha Canyon (~12,400) (3/25/16): light southerly breeze at ridgeline.

- 1200 PM: 0 degrees Celsius on the summit.  Evidence of northerly to westerly winds with previous boot pack and ski tracks blown over in some places. Hand pits: old wind slab below soft recent snow resulted in some clean failures but requiring moderate force. A few isolated areas of sensitive shallow wind slab from previous afternoon's winds.

- 1pm (9,000') north aspect, 32 degree slope: Snow surface slightly moist down to a very firm old wind crust, ~ 8 cm.  ~9,500' steeper (35 deg) northerly facing slopes had small rollerballs forming as a result of skiing. No signs of rollerballs today at least until early afternoon. Evidence of small loose-wet slides on McGee Mountain, east face, ~9500' elevation.  Occurred (Thursday) afternoon, as observers noted clean slopes in the morning, and saw the small slide debris mid-mountain on their return in the afternoon from the highway.  

- Southerly facing slopes bordering Esha Canyon are mostly burned out to ground.  Enough snow in bottom of canyon to skin all the way to the mouth of the canyon bottom at ~8,400'.  A few patches of rock that required booting over. Possible to ski a very small shallow ribbon out of canyon to 8,000' almost to creek but melting super quick!

-Variable snow conditions overall.  North face: wintery, various wind effects with some patches of soft good snow, many stretches of firm wind-board, very limited areas of soft breakable crust.  In canyon, some good stretches of corn snow.

weather

Mon –Tuesday: A very dynamic upper low and cold front will pass over the region Monday with upslope flow increasing snow amounts in the northern part of Mono County and Alpine County. As the upper low settles over the region Monday night we expect periods of snow showers to continue thru Tuesday. The snow showers should result in limited accumulations, mainly at the higher elevations. High temperatures 14-18 degrees below normal Monday will slowly moderate Tuesday.

Wed-Thursday:  Mild and dry weather returns as a ridge of high pressure builds over northeast California and western Nevada late this week with the ridge axis near the West Coast for easterly flow over the region. Slow warm-up during the week with temperatures several degrees below seasonable, 4-8 degrees below normal Wednesday, Thursday 2 to 5 degrees below normal for most areas. Northeast flow will build as the Low slides east Wednesday.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Monday Monday Night Tuesday
Weather: MOSTLY CLOUDY THEN BECOMING CLOUDY. SNOW SHOWERS. MOSTLY CLOUDY. SCATTERED SNOW SHOWERS. MOSTLY CLOUDY. CHANCE OF SNOW SHOWERS.
Temperatures: 24 TO 32 deg. F. 8 TO 15 deg. F. 27 TO 33 deg. F.
Wind direction: WEST NORTH NORTH
Wind speed: 15 TO 25 MPH WITH GUSTS TO 35 MPH. 15 TO 25 MPH WITH GUSTS TO 35 MPH. 15 TO 25 MPH WITH GUSTS TO 35 MPH.
Expected snowfall: 0-2 in. 0-1 in. 0-1 in.
Over 10,000 ft.
  Monday Monday Night Tuesday
Weather: MOSTLY CLOUDY. SCATTERED SNOW SHOWERS IN THE MORNING...THEN SNOW SHOWERS IN THE AFTERNOON. MOSTLY CLOUDY. SCATTERED SNOW SHOWERS. MOSTLY CLOUDY. CHANCE OF SNOW SHOWERS
Temperatures: 22 TO 32 deg. F. 5 TO 13 deg. F. 17 TO 27 deg. F.
Wind direction: SOUTHWEST NORTH NORTHWEST
Wind speed: 45 TO 50 MPH WITH GUSTS TO 75 MPH BECOMING WEST AND DECREASING TO 35 TO 40 MPH WITH GUSTS TO 60 MPH IN THE AFTERNOON. 30 TO 40 MPH WITH GUSTS TO 60 MPH 30 TO 35 MPH WITH GUSTS TO 50 MPH DECREASING TO 15 TO 20 MPH WITH GUSTS TO 30 MPH IN THE AFTERNOON.
Expected snowfall: 0-3 in. 0-2 in. 0-1 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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