Eastern Sierra Avalanche Advisory - 2/24/17

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THIS AVALANCHE ADVISORY EXPIRED ON February 25, 2017 @ 6:52 am
Avalanche Advisory published on February 24, 2017 @ 6:52 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center
bottom line

Although snowfall ended Wednesday morning, upper elevation moderate winds out of the SW to W have continued to load leeward slopes.  Human triggered avalanches will be likely and natural avalanches possible in steep areas that have continued to receive wind-loaded snow.  These sensitive areas are most likely to exist above tree-line on the leeward side of ridges and sidewalls of gullies.  Also small wet point-release natural avalanches will be likely with today’s sunny skies on solar aspects, that could possibly step-down to a larger slab failure.   

How to read the advisory

Bottom Line

Although snowfall ended Wednesday morning, upper elevation moderate winds out of the SW to W have continued to load leeward slopes.  Human triggered avalanches will be likely and natural avalanches possible in steep areas that have continued to receive wind-loaded snow.  These sensitive areas are most likely to exist above tree-line on the leeward side of ridges and sidewalls of gullies.  Also small wet point-release natural avalanches will be likely with today’s sunny skies on solar aspects, that could possibly step-down to a larger slab failure.   

Avalanche Problem 1: Wind Slab
  • Character ?
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    Certain
    Very Likely
    Likely
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    Unlikely
  • Size ?
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  • Trend ?
    Same

Although the recent significant storms are now over with snowfall ending Wednesday morning, moderate SW to W winds have continued to load leeward slopes, especially at upper elevations.  Reports yesterday came in of recent natural avalanche activity that could have taken place as recently as yesterday afternoon as a result of this wind-loading.  As light SW to W winds continue today, with moderate gusts up to 35mph, isolated areas will continue to be wind-loaded.  Wind-slabs heal with sensitivity decreases over time, but just how long this takes from a few hours to a couple days isn’t know.  Be wary of firmer denser snow that could be hollow sounding and the more obvious clue of snow being visibly transported.  Do your own localized stability assessments in safe places, and avoid steep convex areas where it is more likely that a sensitive wind-slab could be triggered.  Also be wary of corniced slopes for two reasons: 1) A cornice breaking underneath you; 2) Wind-loaded slope underneath the cornice.    

Avalanche Problem 2: Loose Wet
  • Character ?
  • Aspect/Elevation ?
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
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  • Trend ?
    Increasing Danger

As clear skies allow the sun to heat up rock-bands and surrounding snow on slopes with solar aspects (E-S-W), small wet point release will be likely, but limited in size due to the continued cold temperatures today.  However, although unlikely, it is possible that a smaller point release could trigger a larger slab failure where a sensitive snowpack exists (more E ot W facing slopes).  

advisory discussion

A solid week of stormy weather came to end this past Wednesday morning, increasing the total snowpack depth by over 40” around Mammoth, 10-15” south toward Bishop, and 20” north toward VA Lakes.  These storms came in with lots of density changes, some periods of upside-down layering (less dense snow under more dense), and lots of wind.  Evidence of small to large natural avalanches were seen throughout the range during this cycle, and even as recently as yesterday due to continued wind-loading.  As winds remain at a light level today, moderate gusts out of the SW to W will continue to move some snow at upper elevations.  Sensitive windslabs will be the greatest concern today, from older ones with more stubborn sensitivity, to fresher very sensitive ones.  The storm slabs that formed during this storm in more sheletered locations have had time to settle and stabilize, which recent snowpack test results have supported.

recent observations

-2/23 - Mammoth - Red Cone - Recent avalanche activity, wind loading

-2/23 - Crowley - Red Mountain - Recent avalanche activity 

-2/23 - Crowley - Red Mountain - Even more recent avalanche activity: Report came in that fairly fresh crisp crown was visible across upper bowls of Red Mountain in the late afternoon (debris D2.5) suggesting continued wind-loading yesterday resulted in slope failure in the afternoon. 

-2/23 - Convict - McGee - After 2pm: Snow banners over high peaks, snow saltation across slopes at 9000'.

-2/22 - June - Mt. Wood avalanche activity, sheltered snow stability

weather

Our break from stormy conditions continues today, with light westerly to southwesterly winds gusting up to 35mph by afternoon, sunny skies with increasing high clouds in the afternoon, and high temperatures in the low 20s at 10,000’. 

For tomorrow (Saturday), expect mostly sunny skies with increasing clouds and a chance of scattered snow showers in the afternoon with less than a half inch of accumulation.  Higher elevation winds will continue out of the W to SW, with gusts into the 60s decreasing to the 40s above 10,000’ by afternoon.  Expect slightly colder temperatures with highs around 20 at 10,000’. 

Long-term:  The Sunday-Monday forecasted Atmospheric River is looking to be loosing strength, with main impacts being increasing high elevation winds, and less than a foot total of new snow over a 2 day period for the northern areas of the forecast area, and much less south of Mammoth.  After this disturbance, it looks to be high and dry through next week, with warming temperatures.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Friday Friday Night Saturday
Weather: Sunny then becoming partly cloudy Partly cloudy Partly cloudy then becoming mostly cloudy. Slight chance of snow in the morning. Chance of snow in the afternoon.
Temperatures: 23 to 29 deg. F. 9 to 15 deg. F. 21 to 27 deg. F.
Wind direction: Variable SW SW
Wind speed: Light winds. Gusts up to 35 mph in the afternoon. 10 to 15 mph. Gusts up to 30 mph increasing to 40 mph after midnight. 10 to 15 mph with gusts to 35 mph in the morning becoming light.
Expected snowfall: 0 in. 0 in. up to 2 in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: Sunny then becoming partly cloudy Partly cloudy Partly cloudy. Slight chance of snow in the morning. Chance of snow in the afternoon.
Temperatures: 17 to 23 deg. F. 5 to 11 deg. F. 14 to 20 deg. F.
Wind direction: W SW W
Wind speed: 15 to 20 mph with gusts to 35 mph 20 to 30 mph with gusts to 45 mph 20 to 30 mph. Gusts up to 60 mph decreasing to 40 mph in the afternoon.
Expected snowfall: 0 in. 0 in. up to 2 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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