Eastern Sierra Snowpack Summary - Apr 18 2016

Our goals are lofty, but our ask is simple... We need your help... Click Here to Find Out How

THIS ADVISORY EXPIRED ON April 21, 2016 @ 6:57 am
Avalanche Advisory published on April 18, 2016 @ 6:57 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center
Avalanche Character 1: 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.

Low to Mid Elevation: Moderate nightly freezes and warming temperatures forecasted for Monday thru Wednesday will maintain the threat for Loose Wet releases on E-S-W-NW aspects. Elevation, aspect, cloud cover and wind can greatly affect how much the snow surface thaws. In general, the snow surface will be frozen/firm early with easterly aspects softening mid morning, southerly aspects softening mid-day, and westerly slopes softening in the afternoon. Lower elevation slopes will soften more quickly with the risk of wet loose activity increasing by the afternoon on solar slopes >35 degrees. Plan your travel to avoid slopes before the snow thaws excessively. Punchy, manky snow past boot-top, and significant recent rollerball activity are indicators the threat of wet loose releases is increasing. Isolated natural and human triggered loose wet avalanches are possible at the mid to lower elevations on solar aspects. While planning your travel in the backcountry take note of the daily High & Low temperatures of nearby remote weather observation stations to determine how well the snow froze over night, which can be a good indicator of how quickly the snow surface will thaw during the day and plan accordingly.

Additional considerations: Spring conditions prevail throughout the region with firm snow conditions during the morning and an elevated risk of slide for life conditions. Use extra caution while traveling in or above hazardous terrain in the AM hours, have the necessary equipment to travel safely (i.e., crampons, ice axe, self-arrest grips), and practice self-arrest in a low risk environment prior to venturing into dangerous environments. 

Avalanche Character 2: 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.

Moderately strong SW-N winds late last week formed isolated Wind Slabs near ridgelines, in depressions and gullies, or adjacent to terrain features in the upper elevation on W-NW-NE-SE-S aspects. These Wind Slabs have had  a couple of days to stabilize but tender isolated Wind Slabs may exist in the upper elevations, especially on N-NE aspects where cool temperatures can slow bonding and strengthening. Though these tender pockets likely wont be big enough to result in a burial, they could entrain or cause a slide into hazardous terrain with potentially high consequences. 

Snowpack Discussion

Primary avalanche focus for Monday thru Wednesday depends on aspect and elevation. Mid to Lower Elevations - isolated natural and human triggered Loose Wet avalanches are possible at the mid to lower elevations on solar aspects. Upper elevations - isolated pockets of Wind Slabs in the upper elevations primarily on N-NE aspects.

Snowpack –The upper elevation northerly aspects are still holding onto to colder conditions with a variety of light crusts, windpack, wind board, and soft snow. Southerly aspects are transitioning toward mature corn. Mid and Lower elevations, the snow surface has undergone extensive melt-freeze cycles and has consolidated into granular melt/freeze snow (corn snow) as the snowpack recedes. Creeks are opening up and snow bridges are sagging and possibly suspect.  

Additional considerations: Spring conditions prevail throughout the region with firm snow conditions during the morning and an elevated risk of slide for life conditions. Use extra caution while traveling in or above hazardous terrain, have the necessary equipment to travel safely (i.e., crampons, ice axe, self-arrest grips), and practice self-arrest in a low risk environment prior to venturing into dangerous terrain. 

recent observations

Red Cone Bowl>McLeod Lake>Twin Lakes, Mammoth Lakes Basin (4/17/16) – On approach (1200): 8700’, Snow Surface 0 ° C, Air Temp 8.6° C, Clear Skies, Wind Calm, Boot Pen 4cm, Ski Pen 3cm. 1300: 9600’, Snow Surface 0 ° C, Air Temp 9° C, Clear Skies, Wind Calm, Boot Pen 4cm, Ski Pen 3cm. 1400: 10,300’, Snow Surface 0 ° C, Air Temp 6° C, Clear Skies, Wind Light/SW, Boot Pen 4cm, Ski Pen 3cm. Summit-Light melt freeze crust forming on North aspects, melt-freeze conditions on NW-W-S-E aspects. Numerous Loose Wet releases (D1) from the previous couple of days on East aspects, 1 small skier triggered Loose Wet (d1) in the bowl (East aspect) Rollerballs along eastern edge of the bowl (West Aspect). Skiing was good with consistent soft conditions, minimal frozen crusts in the trees though a bit sticky.

Mt Dade, Rock Creek (4/16/16) – toured from pack station starting around 830. Turned around just before Mt. Dade because of time constraints and because the snow stayed firm until a later hour than expected. Field weather obs taken on a knob just east of Treasure Lakes at 11250', ESE aspect, at 1115 - Sky: clear; T-air: 0C; T-surf: -1C; T-20: -5C; Wind: Light/ENE, no blowing snow; Snow Surface: MF crust; Boot Pen: 3cm; Ski Pen: 2cm. Several recent D1 wet slides observed between 11500' and 12500' on W and SW aspects of Rosy Finch Peak and Morgan South, also on E and NE aspects of Treasure Peak and Dade. Top of the Hourglass looked scoured down to talus from recent winds. Good coverage everywhere in upper drainage. Snow surface stayed cold longer into the day than expected and skiing was hard snow down to 10800' at noon, corn below.

weather

Mon-Tuesday: Unseasonably warm conditions will persist with the region under high pressure into Tuesday. A weak wave will pass south-to-north along the Sierra associated with an upper low off the California Coast Tuesday afternoon and evening. The high pressure ridge will remain over central Nevada, which will limit the impact of the short wave to the Sierra as the parent low is shunted around the ridge`s western periphery limiting precip to northern CA. Instability factors are favorable for a very isolated thunderstorm with chances around 10% mainly along the Sierra Crest. Temperature are forecasted to be 10-15 degrees above seasonal averages with highs in the upper 60s to lower 70s for Sierra valleys.

Wed-Friday: looks windy as the system approaches the California coast. Peak gusts of 40-60 mph are possible in the higher terrain and along US-395. Latest simulations show the Low tracking a bit farther south and slower, which would favor highest precipitation totals for the Sierra between Lake Tahoe and Mammoth Mtn during the day on Friday.

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: SUNNY CLEAR SUNNY THEN BECOMING PARTLY CLOUDY. SLIGHT CHANCE OF SHOWERS IN THE AFTERNOON.
Temperatures: 56 TO 62 deg. F. 25 TO 32 deg. F. 55 TO 63 deg. F.
Wind direction: LIGHT WINDS LIGHT WINDS BECOMING NORTHWEST LIGHT WINDS
Wind speed: 10 TO 15 MPH WITH GUSTS TO 25 MPH AFTER MIDNIGHT.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Monday Monday Night Tuesday
Weather: SUNNY CLEAR SUNNY THEN BECOMING PARTLY CLOUDY. SLIGHT CHANCE OF SHOWERS IN THE AFTERNOON.
Temperatures: 47 TO 55 deg. F. 24 TO 30 deg. F. 47 TO 55 deg. F.
Wind direction: LIGHT WINDS BECOMING NORTH NORTH LIGHT WINDS.
Wind speed: 10 TO 15 MPH IN THE AFTERNOON. 10 TO 15 MPH WITH GUSTS TO 25 MPH.
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.

ESAC receives support from ...