Eastern Sierra Snowpack Summary - May 01 2016

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THIS ADVISORY EXPIRED ON May 2, 2016 @ 11:12 am
Avalanche Advisory published on May 1, 2016 @ 11:12 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.

Mid to Upper Elevations: Friday’s weak storm deposited 1”to 4” of snow throughout the Sierra Crest. Moderate North to Northeast winds are forecast through Sunday, which will potentially form tender Wind Slabs on NW-W-S-SE-E aspects. Natural releases may be possible, triggered releases are possible. Tender Wind Slabs will most likely be encountered below ridgelines, in gullies/depressions, and adjacent to terrain features that promote drifting. Avoid freshly formed drifts and hollow sounding slabs on steeper terrain. Though these tender pockets may not be big enough to result in burial, they could entrain a rider and carry them into hazardous terrain with potentially high consequences.

 

Avalanche Character 2: Wet Slab
Wet Slab avalanches occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoid avalanche terrain when you see pinwheels, roller balls, loose wet avalanches, or during rain-on-snow events.

Upper Elevations:  Sunday – As skies clear temperatures will rise with solar slopes heat up quickly, especially protected/sheltered areas where the air is relatively calm, which will soften and weaken the surface snow. As temperatures rise through the day, northerly aspects may begin heat-up, shedding some of the recent new snows. Natural Wet Loose releases are possible, triggered releases are probable on slopes of 35 degrees. Be especially cautious on large mountain faces with complex terrain and multiple aspects, which can result in widely disparate warming and weakening of the snow surface.

Mid to Lower Elevations: Loose/Wet Loose releases are possible on slopes of 35 degrees and steeper, especially Sunday as skies clear and temperatures begin to further rise under the intense spring sun. Any new snow will likely easily slough off the underlying snow if disturbed. Natural releases may be possible, human triggered Loose Wet avalanches are probable on solar aspects on terrain ~35 degrees and steeper. These may not be large enough for burial but they could entrain a rider and carry them into hazardous terrain with potentially high consequences. Plan your travels to avoid slopes before the snow heats-up excessively. Punchy, manky snow past boot-top, and significant recent rollerball activity are indicators the threat of wet loose releases is increasing.

 

 

 

 

 

 

Snowpack Discussion

Primary avalanche focus for Saturday: Wind Slabs in the Mid to Upper elevations on E-S-W aspects expanding to NW-N-W-S-SE aspects as winds swing to the Northeast to East Sunday. Mid to Lower Elevations – Loose/Wet Loose avalanches are possible on slopes of 35 degrees and steeper on Saturday, trending toward Loose Wet avalanches Sunday, especially on solar aspects.

Snowpack

Mid to Upper Elevations: The mid to deep snowpack is transitioning to a spring snowpack with minimal layering. On northerly aspects, the upper snowpack remains cool and consists of shallow layers of recent snows that settle and consolidate between intermittent spring storms. Recent northerly winds have strongly affected the NW-NE aspects creating a variety of snow surfaces of wind board, wind slabs, scallops, and soft snow in more protected areas. On solar aspects, the new snow is subjected to intense sun producing alternating layers of melt-freeze crusts and softer unconsolidated snow transitioning toward corn snow on East, South, and West aspects. This has created a series of alternating melt-freeze crusts and soft snow layers on all aspects except North to Northeast aspects in the upper elevations where the snow remains cool enough to limit melt-freeze formation. Overall the recent new snows have bonded well to the underlying snowpack.

Lower elevations: the snowpack consists of consolidated granular snow that has been subjected to extensive melt/freeze cycles with the occasional addition of light snowfalls which quickly melt off or transition to corn as the skies clear between storms.

recent observations

Black Mtn/Red Lake, Virginia Lake (4/29/16): Intended to ascend the Black Mountain to assess snow stability and wind slab distribution. Departed the Turnbull Lake Trailhead for Red Lake Bowl. 1”to 2” at the trailhead with 2”to 3” in the higher elevations.  New snow was moist where exposed to the sun (dry where shaded and unexposed to sun). Lake ice continues to deteriorate, especially around inlets and outlets. Creeks mostly open below 9,800’. Some ski tracks evident in Red Lake Bowl as well as the flanks of South Peak with one party working the main bowl between Mt Olson and South Peak. Ascended up Red Lakes Bowl, 2”-3” new snow throughout the bowl with shallow winds slabs formed along terrain features and in depressions, favoring NE-SE-SW aspects. Wind Slabs nonreactive. Easterly aspects surface snow is moist up to 10,600’. Above, 10, 600’ snow still cold. Moderate Northwest winds were transporting snow onto NE-SE-SW aspects. Black Mountain (North Face), entry almost complete clear of snow, top ¼ strongly wind affected with wind slabs and wind scour. Below, very consistent soft conditions to the valley floor. All test slopes, negative results with no recent avalanches observed. Some rollerballs noted below Red Lakes Bowl summit ridge (NE aspect, 10,600') and on exit below Cooney Lake (10,245’) on NE aspects both natural and skier triggered, primarily in the trees where the air is calmer and warmer.

Black Mtn/Red Lake, Virginia Lake (4/26/16): Departed the Turnbull Lake Trailhead for Red Lake Bow. Snow conditions at the trailhead(11:00): 1”to 2” new, moist where exposed to the sun (dry where shaded and unexposed to sun), air temp 6.4C (43F). Lake ice continues to deteriorate, especially around inlets and outlets. Creeks mostly open below 9,800’. Fair amount ski tracks evident prior as well as multiple parties skiing throughout the drainage. Ascended up Red Lakes Bowl, 2”-4” new snow throughout the bowl with shallow winds slabs formed along terrain features and in depressions, favoring NE-SE-SW aspects. Wind Slabs nonreactive. Easterly aspects developing a melt freeze crust up to 10,400’ (air temp, 4C / 39). Above, 10, 400’ snow still cold.  Time 1300, snow temp -1, air temp + 1 (10,800’), aspect NE. Minor wind transport with the new snow, slowly filling ski and skin tracks. Ascended to the summit of Black Mountain, descend the north face. Top almost complete clear of snow, top ¼ strongly wind affected with multiple horizontal drifts, wind scour, and light breakable crust. Below, very consistent soft conditions to the valley floor. All test slopes, negative results. No recent avalanche observed but extensive rollerballs noted on exit below Cooney Lake (10,245’) on NE aspects both natural and skier triggered, primarily in the trees where the air is calm. 

weather

Saturday: Snow shower activity will diminish with light precip generally limited to Mono-Mineral Counties as drier air spreads south across the region bringing an end to nearly all lingering shower activity. Brisk north to northeast winds with gusts 30-40 mph will keep temperatures across the region a few degrees below average. Winds will diminish in most lower elevations although over the Sierra ridges, northeast to east gusts up to 55 mph will continue through Saturday night.

Sun –Monday: temperatures will warm up to near or slightly above average, with highs near or above 70 degrees for many lower elevations. Chance of precipitation as weak disturbances will produce some instability leading to some showers and thunderstorms forming each afternoon-evening near the Sierra.

Tuesday: Elongated trough off the west coast is expected to progress inland with some model solutions faster with its arrival. Southerly flow will pump moisture into the region with some instability present for isolated showers and possibly a thunderstorm or two with a slight chance precipitation to much of eastern Sierra Tuesday afternoon/evening.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Sunday Sunday Night Monday
Weather: PARTLY CLOUDY THEN BECOMING MOSTLY CLOUDY. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS IN THE AFTERNOON. .MOSTLY CLOUDY THEN BECOMING PARTLY CLOUDY SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS IN THE EVENING. PARTLY CLOUDY. SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS IN THE AFTERNOON.
Temperatures: 44 TO 50 deg. F. 24 TO 31 deg. F. 48 TO 54 deg. F.
Wind direction: NORTHEAST LIGHT WINDS. LIGHT WINDS BECOMING SOUTH
Wind speed: 15 TO 20 MPH WITH GUSTS TO 30 MPH. 10 TO 15 MPH IN THE AFTERNOON.
Expected snowfall: UP TO 1 INCH. UP TO 1 INCH. UP TO 1 INCH. in. UP TO 1 INCH. in. UP TO 1 INCH. in.
Over 10,000 ft.
  Sunday Sunday Night Monday
Weather: PARTLY CLOUDY THEN BECOMING MOSTLY CLOUDY. SCATTERED SNOW SHOWERS AND ISOLATED THUNDERSTORMS IN THE AFTERNOON. MOSTLY CLOUDY THEN BECOMING PARTLY CLOUDY. SCATTERED SNOW SHOWERS AND ISOLATED THUNDERSTORMS IN THE EVENING. PARTLY CLOUDY. SLIGHT CHANCE OF THUNDERSTORMS AND SNOW SHOWERS IN THE AFTERNOON.
Temperatures: 35 TO 43 deg. F. 23 TO 29 deg. F. 39 TO 47 deg. F.
Wind direction: NORTHEAST LIGHT WINDS. LIGHT WINDS BECOMING SOUTH
Wind speed: 20 TO 25 MPH WITH GUSTS TO 40 MPH DECREASING TO 10 TO 15 MPH WITH GUSTS TO 25 MPH IN THE AFTERNOON. 10 TO 15 MPH IN THE AFTERNOON.
Expected snowfall: UP TO 1 INCH in. UP TO 1 INCH in. UP TO 1 INCH. 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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