Issued by Doug Lewis - Eastern Sierra Avalanche Center
Primary avalanche focus for Thursday – Friday: Wind Slabs in the Mid to Upper elevations on NE-SE-SW-W aspects. Mid to Lower Elevations – Loose avalanches are possible on slopes of 35 degrees and steeper on Thursday, trending toward Loose Wet avalanches Friday, especially on solar aspects.
Mid to Upper Elevations: The snowpack continues to transition toward a spring snowpack with corn snow forming on East, South, and West aspects while North to Northeast aspects are still holding onto to colder snow conditions with a variety of light crusts, windpack, wind board, and some soft facets. The snowpack has minimal layering expect the most recent snowfalls, which are quickly capped by melt-freeze crusts as soon as the weather clears. 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 has undergone extensive melt-freeze cycles and has consolidated into granular melt/freeze snow (corn snow) as the snowpack recedes at the lower elevations. Wednesday’s storm delivered light snow with trace to 2” accumulation in the lower elevations.
Thurs-Friday: The main low is expected to pull east of Nevada this afternoon, with back edge of wrap around shower potential near and south of I-80. Instability appears to be too weak for thunderstorms this afternoon. Rain and snow will be minimal. Cool northwest to north surface flow will prevail today, with some stronger gusts up to 35-40 mph possible in southern Mono and Mineral Counties. Shower should diminish Thursday evening over Mono and Mineral Counties with maybe a few weak showers near the Sierra Crest. Generally dry conditions through much of Friday. A low is projected to dive quickly south across Nevada Friday night, bringing increased Northwest to North winds with a chance for precipitation. Strong dynamics and forcing associated with the low could produce some convectively enhanced bands of showers and isolated thunderstorms in Mono County overnight. The Low will bring cooler air to the region with snow down to ~6,000 feet late Friday night.
Sat-Sunday: Light snow accumulations through Saturday morning near the Sierra with showers decreasing. Brisk North to Northeast winds will produce chilly conditions on Saturday. Low pressure will remain over the Great Basin on Sunday, with moist, unstable conditions over the area with chances for showers and even a few thunderstorms on Sunday along the Sierra Crest.
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.
South Pk, Virginia Lks (4/25/16): Snow showers with poor visibility throughout the afternoon hours. Light to moderate Northwest winds with some snow transport evident (scalloping, drifting, etc.). 2” to 6” new snow (powder) over breakable crust (melt-freeze crust on lower angled north aspects, steeper North –Northeast slopes breakable wind crust) with decomposing softer grains underneath. Below this is settled spring snowpack, no real layering. New snow is still cold and has bonded well to the underlying snow. Test slopes yielded no results.
Mid to Upper Elevations: the latest storm deposited 2’ to 8” of relatively low-density snow throughout the Sierra Crest. Moderate North to Northwest winds are forecasted through Friday, which will potentially form tender Wind Slabs on NE-SE-SW-W aspects. Natural releases are possible, triggered releases are probable. 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.
Mid to Lower Elevations: Thursday - Loose releases are possible on slopes of 35 degrees and steeper. Friday – as temperatures begin to warm under the intense spring sun, any new snow may easily slough off the underlying snow if disturbed. Natural releases are 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.
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.