Eastern Sierra Avalanche Advisory - 12/28/17

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON December 30, 2017 @ 6:50 am
Avalanche Advisory published on December 28, 2017 @ 6:50 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Human triggered avalanches will be unlikely, but not impossible, for Thursday and Friday.  The greatest avalanche concern that exists is small isolated areas at and above tree line on non-southerly facing slopes where old stubborn shallow wind slabs rest on top of weaker faceted snow.  While unlikely, harm could come to a person triggering one of these slabs in an area where a fall could result in a slide thru obstacles.  Pay attention to local signs such as shooting cracks or whumphing, which are indications of unstable snow.     

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Above Treeline

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Near Treeline

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Below Treeline
Avalanche Problem 1: Persistent Slab
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While human triggered avalanches are unlikely, avalanche concern still exists in isolated areas where firm dense wind deposits sit on top of weak sugary faceted snow.  Despite the warm daytime temperatures, clear nights have continued to keep the snow surface cold on E-N-W facing slopes resulting in continual weakening of the underlying loose snowpack.  Although a triggered avalanche would likely be small, it could have consequence if it resulted in a fall above dangerous terrain.  Observations have been few, and variability even over short distances can be great, so it is important to make your own assessments in the field.  

advisory discussion

The Ridiculously Resilient high pressure Ridge remains ridiculous and resilient, with no end in sight through at least the middle of next week.  The last weak storm we had was on Dec 21st, which dropped between 1-4” of new snow, with considerable winds, forming dense wind slabs in a variety of locations.  Where these wind slabs sit atop weak sugary faceted snow is where the limited avalanche concern persists.  Despite warm daytime temperatures, the clear cool nights have been continuing the faceting process of the underlying snowpack.  This weak underlying snow will likely become a much more significant concern once we have another snowstorm.  Melt freeze surface crusts have been forming on slopes with sun exposure (more southerly).  Beware of firm conditions and early season obstacles.

recent observations
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12/27 - Mammoth Lakes Basin - Snowpack faceting, variable surfaces

12/27 - VA Lakes - Wind effects, propagation tests

12/25 - Mammoth Lakes Basin - Warming snow surface, facets

Weather and CURRENT CONDITIONS
weather summary

Our charming High Pressure ridge will stick around keeping conditions dry through at least the middle of next week, with above average temps.  Some models are showing a possible break in this high pressure towards next weekend, and maybe even a flurry, while other models are showing dry.  Too early to tell, but doesn’t hurt to hope!  For now (Thursday and Friday), expect sunshine, temperatures reaching 50 degrees near 10,000’, and light winds with moderate gusts. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Thursday Thursday Night Friday
Weather: Sunny Clear Partly cloudy
Temperatures: 49-57 deg. F. 24-34 deg. F. 52-58 deg. F.
Wind Direction: W SW SW
Wind Speed: light rising to 10 mph in the afternoon 10 mph 10 to 20 mph. Gusts up to 30 mph in the afternoon
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Thursday Thursday Night Friday
Weather: Sunny Clear Partly cloudy
Temperatures: 44-50 deg. F. 27-35 deg. F. 45-51 deg. F.
Wind Direction: N shifting to W in afternoon W W
Wind Speed: 10 to 20 with gusts up to 35 mph. 10 to 20 mph with gusts to 30 mph. 20 to 30 mph. Gusts up to 40 mph increasing to 50 mph in the afternoon.
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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