Issued by Doug Lewis - Eastern Sierra Avalanche Center
This is the last Snowpack Summary to be issued for the 2015-16 season. The local support and enthusiasm for the Center’s mission has been truly overwhelming. On behalf of the Eastern Sierra Avalanche Center, I would like to thank the Eastern Sierra backcountry community for helping to make this an incredibly successful season. Your support, contributions, observations made it possible and we look forward to serving the community next season.
Primary avalanche focus for Monday thru Wednesday: All Elevations - Loose Wet avalanches possible on slopes of 35 degrees and steeper, especially solar aspects as the temperatures warm. Mid to Upper elevations – isolated pockets of Wind Slab on W-N-E aspects.
Mid to Upper Elevations: The mid to deep snowpack is transitioning to a spring snowpack with minimal layering. On northerly aspects, has remained cool with the upper snowpack remains consisting 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.
Monday: A weak shortwave brushing across northern CA will lead to some shower and isolated thunderstorm activity mainly across northeast CA and near the Sierra this afternoon and early evening. Most of these cells will move to the north or northwest.
Tues. – Wednesday: a large low pressure over the eastern Pacific moves slowly east, reaching the California coast by Wednesday. The increased upper level divergence ahead of the Low, along with an influx of moisture will bring increased chances for showers and thunderstorms across the region. The best potential for shower and thunderstorms will be over northeast CA and the northern Sierra.
Wednesday: An upper level jet streak rotates around the Low with the favorable left exit region possibly providing enhanced lift over parts of eastern CA. Some uncertainty remains with the location of this enhanced lift, but areas could see more organized and stronger storms with potential for heavy precipitation. However, instability may be reduced due to widespread cloud cover and increased wind shear aloft. In this less unstable scenario, areas of light to moderate rain may still occur with more isolated thunder. Slight changes in timing and location of the upper jet could bring either scenario Wednesday afternoon or evening.
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.
Upper Elevations: Clearing skies, light winds, and rising temperatures are forecasted for Mon-Tuesday, which will allow the sun to quickly heat-up the surface snow, especially solar aspects. As temperatures rise through the day, northerly aspects may begin to heat-up and weaken the surface snow, which could result in shedding of the recent new snows. Natural Wet Loose releases are possible, triggered releases are probable on slopes of 35 degrees, especially solar aspects. Use extra caution on large mountain faces with complex terrain and multiple aspects, which can result in widely disparate warming and weakening of the surface snow.
Mid to Lower Elevations: Loose Wet releases are possible on slopes of 35 degrees and steeper as skies clear and temperatures begin to rise under the intense spring sun. Any new snow will likely easily slough off the underlying snow if disturbed. Natural Loose Wet releases are possible, human triggered Loose Wet avalanches are probable on solar aspects on terrain ~35 degrees and steeper. Though these avalanches may not be large enough for burial, 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 and be willing to adjust your travel plan as conditions change. Indicators the threat of Loose Wet releases is increasing: observed slides, punchy or manky snow past boot-top, and significant recent rollerball activity.
Mid to Upper Elevations: A series of weak storms have deposited several inches of new snow throughout the Sierra Crest over the past week. Moderate North to Northeast winds during the week formed isolated tender Wind Slabs on NW-SW-SE aspects. Though these Wind Slabs have had a brief time to settle, warming temperatures may cause them to weaken and become reactive. Light Southerly winds are forecasted for the next couple of days, which may form new isolated Wind Slabs on W-N-E aspects. Isolated natural and triggered releases may be possible on slopes of 35 degrees and steeper. Wind Slabs may be encountered below ridgelines, in gullies/depressions, and adjacent to terrain features that promote drifting. Use extra caution around 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.
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.