Eastern Sierra Avalanche Advisory - 3/12/17

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THIS AVALANCHE ADVISORY EXPIRED ON March 13, 2017 @ 6:27 am
Avalanche Advisory published on March 12, 2017 @ 6:27 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center
bottom line

Sunday - the main avalanche concern is Loose Wet releases. Unseasonably warm temperatures forecasted for Sunday will produce small loose-wet point releases on E-SE-S-SW-W in the mid to upper elevations. Lower Elevations the range will expand to include NW/NE as well. Natural releases likely on solar aspects, triggered releases probable in steeper terrain. Timing is critical to avoid for wet loose avalanches. Small point releases are indicators that surface snow is loosing strength and becoming unstable, larger avalanches may be possible. Caution - small slides can easily entraining a rider and carry them into dangerous terrain and in rare instances could entrain enough snow to potentially bury a person, especially where a terrain trap is involved.  

 

How to read the advisory

Bottom Line

Sunday - the main avalanche concern is Loose Wet releases. Unseasonably warm temperatures forecasted for Sunday will produce small loose-wet point releases on E-SE-S-SW-W in the mid to upper elevations. Lower Elevations the range will expand to include NW/NE as well. Natural releases likely on solar aspects, triggered releases probable in steeper terrain. Timing is critical to avoid for wet loose avalanches. Small point releases are indicators that surface snow is loosing strength and becoming unstable, larger avalanches may be possible. Caution - small slides can easily entraining a rider and carry them into dangerous terrain and in rare instances could entrain enough snow to potentially bury a person, especially where a terrain trap is involved.  

 

Avalanche Problem 1: Loose Wet
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Increasing Danger

Recent warm temperatures and sunny skies are generating Loose Wet releases on solar aspects (E-SE-S-SW-W) in the mid to upper elevations. Lower elevations NE-E-SE-S-SW-W-NW. In the lower elevations where there’s a shallower snowpack there maybe a buried weak layer that can be triggered by larger point releases overloading it and stepping down into this layer and possible propagating into a larger slab failure. Timing is critical to avoid wet loose avalanches with easterly aspects thawing first, then south, then west in the late afternoon. Small point releases are indicators that surface snow is loosing strength and becoming unstable, larger avalanches may be possible. Caution - small slides can easily entraining a rider and carry them into dangerous terrain.

 

advisory discussion

High pressure entrenched off the California coast has ushered in an extended period of spring-like weather, which has rapidly shifted the snowpack from a winter-like snow regime toward spring-like snow conditions, with the accompanying melt/freeze cycles, on solar aspects as the sun races toward the spring equinox (March 21). Cloudy skies Friday night, kept temperatures above freezing to nearly 11,000’. Warm temperatures Saturday on solar aspects softened the snow with the upper 30 to 45 cm of the snowpack becoming wet with small wet point releases were reported. The recent warm-up has even impacted the northerly aspects (~ below 9000’) where the snow has turned sticky and thick (aka Manky).

The last snowfall in the area occurred on Sunday (3/5) , and was accompanied by very strong SW to West winds through Monday forming Windslabs  on exposed W-NW-N-NE-E-SE aspects at all elevations with the mid to upper elevations most heavily impacted. The Windslabs that formed during that storm event have had six days to stabilize. Since then, spring like conditions have dominated the region with above average temperatures and low winds. As temperatures climbed the avalanche focus shifted toward loose-wet point releases on solar aspects in the mid to upper elevations, all aspects in the lower elevations, especially when the overnight low temperatures are only near or above freezing.

With spring conditions comes firm melt-freeze crusts on solar aspects in the AM hours (possibly later) and firm wind-board on more northerly aspects. These snow conditions make an arrest difficult on steeper terrain if a fall occurs (Slide For Life). If these conditions are encountered, crampons, ice ax, or a whippet maybe required to travel safely in steep terrain. Caution in complex terrain with multiple aspects. Careful snow assessment is recommended, reevaluate your plan as needed, be prepared to alter your objective. 

weather

Sunday thru Monday – High pressure will dominate the forecast through the first part of the week with mostly sunny skis today and into Monday. Temperatures will remain well above normal for this time of year with upper 50s to low 60s in the Sierra valleys.

Tuesday thru Wednesday – High pressure ridge will persist for the balance of next week with only a glancing blow from a couple of shortwaves moving through the Pacific Northwest into the northern Rockies late. Gusty winds will precede the front along with slightly cooler temperatures, which will remain well above average with lows at least slightly above average for mid-week into next weekend. 

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: Sunny Clear Sunny
Temperatures: 52 to 58 deg. F. 26 to 32 deg. F. 53 to 59 deg. F.
Wind direction: Light winds Light winds Light winds
Wind speed:
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Sunday Sunday Night Monday
Weather: Sunny Clear Sunny
Temperatures: 45 to 53 deg. F. 23 to 29 deg. F. 46 to 54 deg. F.
Wind direction: Light winds Light winds Light winds
Wind speed:
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer
This Avalanche Advisory is designed to generally describe avalanche conditions where local variations always occur. This product only applies to backcountry areas located outside established ski area boundaries. 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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