Eastern Sierra Avalanche Advisory - 2/13/17

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THIS AVALANCHE ADVISORY EXPIRED ON February 15, 2017 @ 5:50 am
Avalanche Advisory published on February 13, 2017 @ 5:50 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center
bottom line

The primary avalanche concern for Wednesday thru Thursday will be increasing wind slabs at middle and upper elevations as pre-frontal Southwesterly winds increasing Thursday. Wind Slabs will likely be encountered primarily on NW-N-NE-E-SW aspects but may be encountered on other aspects due to localized edding. Wednesday, ahead of the next system warm temperatures will maintain the threat of loose wet avalanches on solar aspects at middle and lower elevations. Wednesday: Above about 9000 feet, natural avalanches are unlikely, but human triggered avalanches possible. Evaluate snow and terrain carefully and identify windloaded features such as below ridgelines and along the sidewalls of gullies. Thursday: natural avalanches possible; human- triggered avalanches likely on wind loaded slopes in the mid to upper elvations.

Wednesday: Below ~ 8000 feet, both natural and human triggered avalanches will remain unlikely. 

Thursday: natural and human triggered avalanches will remain unlikely but Isolated pockets of Wind Slab may form Thurday in favored locations (gullies, shallow depressions, rock outcroppings, etc.) if the snowline falls further than forecasted.

 

How to read the advisory

Bottom Line

The primary avalanche concern for Wednesday thru Thursday will be increasing wind slabs at middle and upper elevations as pre-frontal Southwesterly winds increasing Thursday. Wind Slabs will likely be encountered primarily on NW-N-NE-E-SW aspects but may be encountered on other aspects due to localized edding. Wednesday, ahead of the next system warm temperatures will maintain the threat of loose wet avalanches on solar aspects at middle and lower elevations. Wednesday: Above about 9000 feet, natural avalanches are unlikely, but human triggered avalanches possible. Evaluate snow and terrain carefully and identify windloaded features such as below ridgelines and along the sidewalls of gullies. Thursday: natural avalanches possible; human- triggered avalanches likely on wind loaded slopes in the mid to upper elvations.

Wednesday: Below ~ 8000 feet, both natural and human triggered avalanches will remain unlikely. 

Thursday: natural and human triggered avalanches will remain unlikely but Isolated pockets of Wind Slab may form Thurday in favored locations (gullies, shallow depressions, rock outcroppings, etc.) if the snowline falls further than forecasted.

 

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

Moderate Southwesterly winds accompanying the arrival of the next system Thursday will form wind slabs leeward slopes. Heightened avalanche conditions exist on NW-N-NE-E-SE primarily on wind loaded terrain at upper and middle elevations.  However, Wind Slabs may be encountered on other aspects due to localized edding. Be wary of hollow, drum-like sounding snow or cracks shooting out from your feet. Thursday (~below 8000'), isolated pockets of Wind Slab may form in favored locations (gullies, shallow depressions, rock outcroppings, etc.) if the snowline falls further than forecasted. 

 

Avalanche Problem 2: Loose Wet
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Decreasing Danger

Warm temperatures thru Wednesday will continue to drive Loose Wet releases, especially around rock outcrops and below cliff bands. Time of day is critical with east aspects receiving the first radiation of the day, then south, then west. Watch out for pinwheels rolling down the slopes around and above you.

advisory discussion

The past week’s storm was accompanied by warm temperatures and a moderate southwest flow. Heavy wet precipitation kicked off a huge cycle of natural avalanches through Saturday. Reports from across the forecast area of wet slab, storm slab, and wind slab activity came pouring in. Temperatures cooled late in the week with lingering showers, and 6 to 30 inches of lighter, transportable snow at the surface was deposited as sensitive wind slabs on leeward slopes. Many of these slabs ran naturally Friday and Saturday or were kicked off intentionally by parties testing slopes. The remaining slabs on northeast aspects have gained strength and become more stubborn to trigger. Then the wind shifted post-storm to the northeast and blew some of the remaining soft snow onto southerly aspects. Winds yesterday were variable and localized wind slabs may have formed in other areas as well. Wind affected snow has been found lower in elevation than usual. These newer wind slabs have ranged from stubborn to touchy and may still take a day or two to stabilize.

Once the sun appeared again over the weekend, the intense solar radiation quickly warmed rocks and cliff bands as well as the surrounding snow. Reports of loose snow avalanches and roller balls began to appear Saturday and continued into Sunday afternoon. At lower elevations across the forecast area melt-freeze crusts were beginning to form. Temperatures will warm again a few degrees over the next two days; highs will reach the 40s even above 10,000 feet. Cloudy skies tonight and Tuesday may provide some shade, but may also prevent some of that solar energy from escaping into the atmosphere keeping the upper snowpack warm. This will extend the chance of wet point releases. Time of day is critical when evaluating your exposure to wet loose avalanches. East aspects will warm first in the morning and the action will follow the sun as it moves across the sky warming south and then west facing slopes in the afternoon. Be on the lookout for moist surface snow, pinwheels rolling down around you, and steep rocky terrain.

weather

 

...HIGH WIND WATCH IN EFFECT FROM LATE TONIGHT THROUGH THURSDAY AFTERNOON...

Dry conditions with increasing clouds ahead of the next system. Thursday will feature a windy day with mountain snow and lower valley rain. Friday into Saturday brings another system with less wind but additional rain and higher elevation snow. There will be a brief break before a much stronger storm brings wind and more significant precipitation early next week. 

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 then becoming mostly cloudy. Mostly cloudy. Cloudy with snow.
Temperatures: 42 to 48 deg. F. 29 to 34 deg. F. 31 to 37 deg. F.
Wind direction: Light winds becoming southwest Southwest Southwest
Wind speed: 10 to 15 mph with gusts to 30 mph in the afternoon. 15 to 25 mph. Gusts up to 40 mph increasing to 70 mph after midnight. 20 to 35 mph with gusts to 85 mph.
Expected snowfall: 0 in. 0 in. up to 6 in.
Over 10,000 ft.
  Monday Monday Night Tuesday
Weather: Sunny then becoming mostly cloudy. Mostly cloudy. Cloudy with snow.
Temperatures: 36 to 42 deg. F. 25 to 30 deg. F. 26 to 32 deg. F.
Wind direction: Light winds becoming southwest Southwest Southwest
Wind speed: 10 to 15 mph with gusts to 40 mph in the afternoon. Southwest 15 to 25 mph with gusts to 50 mph increasing to 25 to 35 mph with gusts to 85 mph after midnight. 40 to 60 mph. Gusts up to 110 mph increasing to 125 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 2 to 6 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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