Avalanche Advisory: Sunday - Dec 2, 2018

Avalanche Advisory published on December 2, 2018 @ 6:44 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

*Bottom line UPDATE for Monday - Natural and human triggered avlanches are unlikely, but small avalanches are not impossible in isolated areas or extreme terrain at upper elevations where a wind slab with lingering sensitivity may still exist on SE-S-N-NE terrain.  Next FULLY updated advisory will be published Tuesday morning.  

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Above Treeline

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Near Treeline

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Below Treeline
Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Moderately heavy snowfall from mid-morning thru mid-afternoon yesterday (Saturday) accompanied by STRONG SW winds created widespread wind slabs on leeward terrain at all elevations.  SE-E-N-NW facing slopes will be most concerning especially at tree line and above, but wind slabs will likely also be found at lower elevations and in typically more sheltered terrain due to the strength of yesterday’s winds.  Be on the lookout for denser snow deposits and clues such as cornices and wind ridges to help determine where these slabs may exist.  As time passes these wind slabs will become less sensitive and more stable.  Watch for signs such as shooting cracks, and do your own localized assessments to see how these wind slabs are bonding over the next two days before committing to steeper potentially wind-loaded terrain.  Avalanches could be large enough to bury a person.   

advisory discussion

Thanksgiving was the first real storm of the season.  Dropping a foot+ of snow above 9000’, it paved the way for this week’s colder Wednesday-Thursday storm which dropped another 2-3’ of snow, with highest amounts recorded around Tioga Pass and Snow levels reaching down to 6000’.  The sun came out on Friday and everywhere the eye could see was a beautiful winter wonderland.  Along with the sun, winds increased Friday as well at higher elevations adding some impressive snow banners blowing off of peaks, before calming considerably Friday evening.  Small cornice collapses were observed over the Sherwin ridgeline Friday evening as a result of those winds which redistributed snow onto leeward slopes, and surely created some fresh wind slabs especially in exposed areas at tree-line and above.  Saturday morning started off clear, but quickly turned stormy mid-morning with moderately heavy snowfall and STRONG SW winds which persisted into late afternoon.  Some hardy split-boarders made it out to Redcone bowl and found some great skiing on its western slopes which the SW winds weren’t loading, but wisely stayed away from the more suspect north slopes.  While ESAC was hosting it’s spectrum of avalanche clinics at it’s season kick-off event at Main Lodge on Mammoth Mtn, hardy skiers and boarders riding lifts outside in the storm were finding some of the best turns of the year.  

Much in contrast to last season, the underlying snowpack to the ground this season at this time does not have suspect weak layers lurking, since all of the snow on the ground has fallen so recently.  Our biggest avalanche concern for today (Sunday) will be surface instabilities in the form of wind slabs at mid to upper elevations as a result of the STRONG SW winds that blew most of yesterday (Saturday) which re-distributed some of the 2-3’ of soft snow that fell mid-week and blew the fresh 4-10” of snow that came down yesterday (Saturday) into fresh wind slabs on leeward terrain at all elevations.  With sunny skies and calm conditions Sunday and Monday, these wind slabs will strengthen and become less concerning with time.  It will be important for backcountry users to recognize where wind slabs may be and do their own localized assessments of wind-deposited slopes to see just how these new wind slabs are bonding.  

Keep in mind the coverage is still thin!  Despite the appearance of smooth snow covered slopes, rocks, tree stumps and logs are lurking just under the surface.  Don’t end your season with an injury before it really even begins!


weather summary

Expect sunny skies, light winds and chilly temperatures for Sunday and Monday.  Sunday will be considerably colder than Monday. Clouds begin to thicken Monday night as the next low pressure system moves into our area off of the Pacific bringing good chances of light snow from Monday night thru Thursday.  

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 Partly cloudy then becoming clear Mostly sunny
Temperatures: 18 to 24 deg. F. 5 to 11 deg. F. 26 to 32 deg. F.
Mid Slope Winds: N/A N/A N/A
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Sunny Partly cloudy then becoming clear Mostly sunny
Temperatures: 11 to 16 deg. F. 1 to 7 deg. F. 20 to 25 deg. F.
Ridge Top Winds: West to northwest Southwest Southwest
Expected snowfall: 0 in. 0 in. 0 in.
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 Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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