Avalanche Advisory: Saturday - Dec 8, 2018

THIS AVALANCHE ADVISORY EXPIRED ON December 9, 2018 @ 7:00 am
Avalanche Advisory published on December 8, 2018 @ 7:00 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

SW winds increased last night.  Human triggered wind slab avalanches will be possible on exposed SE-E-N-NW facing steep terrain on the leeward side of ridges, cross loaded gullies and around other features that promote drifting at upper elevations. Evaluate snow and terrain carefully.  Early season obstacles exist!

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Below Treeline
Avalanche Problem 1: Wind Slab
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Mid to upper elevation winds increased for the first time last night since up to 8” of light snow fell earlier this week.  These SW winds in the mid-30 mph range will continue this morning before decreasing in the afternoon.  With adequate light snow available for transport, be on the lookout for fresh wind slabs sensitive to human triggering in exposed terrain facing SE-E-N-NW at upper elevations. Blowing snow and cornice formation can give you clues as to where these slabs may be, and realize that slight terrain variations can lead to very variable distribution of these slabs. While these wind slabs are expected to be on the smaller side, they could still be large enough to cause a bad fall and potentially bury a person especially if a terrain trap is involved.  Do your own localized assessments before committing to steep terrain where fresh wind slabs may be.

advisory discussion

Up to 8” of very light snow fell with very light winds on Tuesday and Wednesday on top of a very stable underlying snowpack.  The sun came out yesterday with warmer temperatures and caused some small loose wet point releases on sun-exposed slopes.  Last night winds increased at mid to upper elevations for the first time since the new snow fell creating a wind slab avalanche problem for today in specific areas.  While sunny skies today will still cause some small loose wet activity at lower elevations, this slope warming will be moderated by the wind at higher elevations. 

We spoke of an interesting frozen surface film / thin humidity / zipper crust that formed on slopes throughout the mammoth crest zone a few days ago.  Observations yesterday confirmed that it did get completly faceted away and is now undetectable.      

Early season obstacles exist!  Plenty of rocks, logs, and tree stumps are lurking just under the surface, which has led to injury and broken equipment already.  Take your time, be careful, and don’t end your season before it barely begins! 

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12/7 - Mammoth area - Earthquake Dome: Stable conditions, settlement, surface hoar on ridgetop

12/7 - Mammoth area - Mammoth Crest: Surface facets, surface Hoar, thin condiitons.

Weather and CURRENT CONDITIONS
weather summary

Sunny skies, even warmer temperatures, and moderate mid to upper elevation SW winds in the mid 30mph range are expected today for the mountains.  These winds will decrease in the afternoon.  A temperature inversion will likely keep lower elevations below 7000’ cooler and in the clouds.  Clouds will return throughout the day on Sunday, along with increased SW winds as another weak low-pressure system makes its way inland, with a slight chance of flurries Monday night.   

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Saturday Saturday Night Sunday
Weather: Sunny Clear Partly cloudy then becoming mostly cloudy
Temperatures: 36 to 41 deg. F. 16 to 21 deg. F. 34 to 40 deg. F.
Mid Slope Winds: Light winds becoming south after midnight Southwest
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Sunny Clear then becoming partly cloudy Partly cloudy then becoming mostly cloudy
Temperatures: 33 to 38 deg. F. 13 to 18 deg. F. 27 to 32 deg. F.
Ridge Top Winds: Southwest Southwest Southwest
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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