Eastern Sierra Snowpack Summary - Mar 31 2016

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THIS ADVISORY EXPIRED ON April 2, 2016 @ 6:40 am
Avalanche Advisory published on March 31, 2016 @ 6:40 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.

Isolated wind slabs are the key concern in the mid to upper elevations where winds can easily transport the new snow to: leeward slopes, below ridgelines, crossloaded gullies & depressions, and drifts around terrain features. The recent East to Northeast winds are forecasted to continue for the next two days and will favor further isolated wind slab formation on exposed/wind prone SE-S-SW-W-NW aspects. Assess wind slab stability while ascending and prior to committing to complex terrain. 

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.

As temperatures begin to rebound over the next two days the threat of Loose Wet will rise on solar aspects and are most likely mid-morning to mid-day, depending on aspect and localized heating. Generally, the hazard rises in the morning for E-SE aspects, SE-SW mid-day, and westerly aspects by afternoon. Use extra caution while traveling in complex terrain with multiple aspects where localized heating can produce extensive loose slides. Triggered Loose Dry slides are a concern on steep northerly slopes where the snow is protected from the wind and has yet to settle and bond to the underlying melt-freeze crust on solar aspects or where there is extensive wind pack in mid and upper elevations. These slides may be small in size but can quickly overtake a rider and possibly carrying them into hazardous terrain.  

 

Snowpack Discussion

Primary avalanche issue is focused on the mid to upper elevations for wind slabs recently deposited on the melt freeze crust on solar aspects or on firm windpack found on northerly aspects. Either interface can slow bonding and act as a good bedsurface. Secondary avalanche issue: As temperatures warm, the threat of wet loose will likely rise on solar aspects. Triggered Dry Loose avalanches on steep, where the snow remains unwind affected and is not yet settled or well bonded to the underlying snow

Snowpack - The recent cool temperatures and occasional light snowfalls have helped slow the steady retreat of the snowline at the lower elevations (~7,700 - ~9,000’). The snow at this elevation has cycled through extensive melt-freeze cycles with no major layering other than the recent new snow but is currently very icy at the interface and will slow new snow bonding as well as make for a good bedsurface. Mid and upper elevation snowpack is easing toward a spring snowpack with multiple melt-freeze crusts with a relatively strong upper and mid snowpack. The Low that lingered for a good part of the week has delivered 2-7” of snow throughout the region. The new snow continues to form bonds to the underlying snow interface.

 

 

recent observations

Treasure Lakes Basin via South Lake Road (March 30, 2016), objective - Mt. Johnson but retreated due to poor visibility. South Lake TH was approx. 30-minute skin from where we parked below Parchers Resort. Summer trail had thin snow cover immediately above the lake but coverage improved quickly. Cloud ceiling was in and out of the Treasure Lakes basin throughout the morning and the clouds finally settled in the South Fork drainage around 1:00 p.m. Snowfall intensity increased from periodic showers (S-1) to steady snow (S1) by 2:00 p.m. Winds were North throughout the day. Calm to Light in the a.m. increasing to Moderate in the afternoon. 3-4" light new snow below treeline. 6-10" new snow above treeline. Beneath new snow was primarily a firm old snow surface (MfCr and old wind pack).

We observed several recent D1 Loose Dry avalanches on North aspects in very steep terrain, especially beneath rock-bands and originating in small couloirs. Active light snow transport by North winds above treeline. Great powder skiing on North aspects with very little wind effect.

Tour- June Lake Ski Area>Hourglass>Fern Creek>Yost Lake>June Lake Ski Area (3/29/16) 1200, Skies clear, Early melt cycle snow on E-S-W aspects, ~10,000’ and below. Ski penetration 2-4 cm. NE-N aspects, ~ 9700’ still cool with mix of windboard, wind scallops, soft facets, and firm wind slab. Upper Hourglass light melt freeze crust forming, temps remain cool, light melt-freeze crust over 2-4cm new snow, patchy in places due to wind, snow wind loaded onto North-Northeast aspects. Old melt-freeze crust on Southeast to South aspects. Summit ridge (1400) Partly Cloudy, clouds building from the SW, light to moderate SW winds, and upper descent into Fern Creek mixture of Sastrugi, ice, and patches of freshly transported snow, down to ~10,200. Below well formed ribbons of soft snow (5-10cm) over very icy/firm base to Fern Lake. Fern Lake (1430), mostly cloudy, snow flurries forming over the higher elevations. 1-3cm of new snow over breakable melt-freeze crust over 4-8cm loose dry to moist snow underneath, depending on aspect from Fern Lake to ski area boundary. Test slopes yielded no results. Light snow transport noted during the day on N-NE aspects. 

weather

Thurs-Friday: The upper level low which has brought the Sierra much cooler weather and light snow is slowly exiting the region. A ridge of high pressure builds in Thursday through the weekend bringing warmer temperatures and generally light winds with high temperatures likely rise the 60s in Sierra valleys Friday.

Sat-Sunday: The Sierra Front is likely to see weak breezes (aka Zephyr), with gusts around 20 mph. A weak shortwave trough will track across northern California by Saturday afternoon; locally the impact will be an increase in clouds and the potential for showers. Generally quiet weather is expected Sunday, as weak SW flow aloft will keep dry and mild conditions over the region with afternoon cumulus coverage and light zephyr breeze. There is a very slim possibility of isolated late day showers, appears too limited to a few brief sprinkles.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Thursday Thursday Night Friday
Weather: SUNNY CLEAR SUNNY
Temperatures: 44 TO 49 deg. F. 25 TO 30 deg. F. 48 TO 53 deg. F.
Wind direction: NORTHEAST EAST EAST
Wind speed: 10 TO 15 MPH. GUSTS TO 30 MPH IN THE MORNING. 10 TO 20 MPH 10 TO 15 MPH BECOMING LIGHT
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: SUNNY CLEAR SUNNY THEN BECOMING PARTLY CLOUDY
Temperatures: 37 TO 44 deg. F. 25 TO 30 deg. F. 42 TO 48 deg. F.
Wind direction: NORTHEAST NORTH BECOMING NORTHEAST NORTHEAST
Wind speed: 20 TO 30 MPH WITH GUSTS TO 50 MPH 25 TO 30 MPH WITH GUSTS TO 40 MPH, 15 TO 20 MPH AFTER MIDNIGHT. 15 TO 20 MPH DECREASING TO AROUND 10 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.

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