Avalanche Advisory: Wednesday - Dec 26, 2018

THIS AVALANCHE ADVISORY EXPIRED ON December 28, 2018 @ 6:58 am
Avalanche Advisory published on December 26, 2018 @ 6:58 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Wednesday: Human triggered wind slab avalanches will be possible in exposed mid to upper elevation areas.  4-6” of new snow fell late Christmas-eve night accompanied by strong SW winds, which shifted out of the N yesterday, and will continue out of the NW today.  Due to this wind shift, be on the lookout for sensitive wind slabs on all aspects just below ridgelines, the sidewalls of gullies, and around other features that promote drifting.  

Thursday: While smaller and more isolated, human triggered wind slab avalanches could still be possible today at exposed mid to upper elevations.  These will most likely be found on NE-E-S-SW facing slopes as winds continue out of the W and NW.

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Avalanche Problem 1: Wind Slab
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3-6” of new snow fell along with moderate SW winds on Christmas-eve night.  Winds shifted out of the north for all of Christmas day with speeds reaching 60-90 mph over ridgetops.  Today (Wednesday) winds are expected to continue at more moderate speeds out of the NW.  While NE-E-S-SW facing slopes will be of greatest concern for fresh wind slabs sensitive to human triggering, there could remain wind slabs with lingering sensitive on the remaining aspects as well.  Watch for areas of denser wind deposited snow, especially just below ridgelines and around other terrain features that promote drifting.  Do your own localized assessments to determine how fresh and sensitive wind slabs are before committing to steeper terrain where wind slabs may exist.  While likely small, a resulting slide could lead to a nasty fall and a potential burial especially if a terrain trap is involved.  If in doubt, stick to lower angled sheltered slopes.  

For Thursday, this concern will decrease and become even more isolated to NE-E-S-SW facing slopes as N to W winds continue. Continue to do your own localized assessments before committing to steep consequential terrain.   

advisory discussion

The modest Christmas-eve night storm came in right-side-up starting warm and finishing cold.  Overall new storm snow bonded well, leaving the avalanche concern focused on fresh and lingering wind slabs.  Prior to this latest storm, faceted weak snow has been found in many areas at the surface of the snow pack, or just below old dense wind slabs.  Tests continue to show these young facets to have the potential to be reactive, but do to the relatively small amount of new snow, they are not nearly as concerning as they would be if than if we got a much bigger dump.  None-the-less, these now slightly deeper layers are worth monitoring as a potential concern for future bigger storms.  

Weather and CURRENT CONDITIONS
weather summary

For Today (Wednesday) expect northwest winds to continue at moderate speeds, partly cloudy skies, and temperatures reaching the low 30s around 10,000’.  Winds will shift more out of the west for a period tonight, before shifting back to northwest at moderate speeds for Thursday with mostly cloudy skies, slight chance of snow showers, and COLD temperatures barely breaking out of the teens around 10,000’.   

The rest of the year looks to be cold and dry.  Fingers crossed for 2019!    

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Partly cloudy. Partly cloudy then becoming mostly cloudy. Slight chance of snow showers after midnight. Snow levels below 7000 feet. Chance of precipitation is 10%. Mostly cloudy. Slight chance of snow showers. Snow levels below 7000 feet. Chance of precipitation is 20%.
Temperatures: 33 to 38. deg. F. 12 to 18. deg. F. 19 to 25. deg. F.
Mid Slope Winds: Northwest 10 to 15 mph with gusts to 35 mph. West 15 to 20 mph with gusts to 40 mph. North 15 to 25 mph with gusts to 45 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. Up to 1 inch. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Partly cloudy. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%. Mostly cloudy. Slight chance of snow showers. Snow levels below 7000 feet. Chance of precipitation is 20%.
Temperatures: 28 to 33. deg. F. 8 to 13. deg. F. 15 to 21. deg. F.
Ridge Top Winds: Northwest 20 to 30 mph with gusts to 50 mph. Northwest 15 to 30 mph with gusts to 45 mph shifting to the west 25 to 35 mph with gusts to 60 mph after midnight. Northwest 20 to 30 mph with gusts to 50 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. Up to 1 inch. | SWE = less than 0.10 inch. 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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