Avalanche Advisory: Monday - Dec 17, 2018

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THIS AVALANCHE ADVISORY EXPIRED ON December 18, 2018 @ 6:25 am
Avalanche Advisory published on December 17, 2018 @ 6:25 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Avalanche danger will be elevated today as moderate SW winds redistribute the 3-5” of new morning snowfall into unstable wind slabs.  Human triggered avalanches will be likely and natural avalanches possible on exposed leeward slopes facing SE-E-NE-N-NW at mid to upper elevations.  Thin snowpack, early season obstacles exist!

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Below Treeline
Avalanche Problem 1: Wind Slab
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Moderate SW winds will continue to form fresh sensitive wind slabs throughout the day even after snowfall stops this morning.  3-5” of new snow is plenty for this wind to create dangerous wind slabs that could take a rider on a violent ride and leave them partially or even possibly fully buried.  Avoid denser smooth wind deposits on the leeward side of ridges, sidewalls of gullies, and around other features that promote drifting.  Wind slab deposition can be VERY variable across a slope.  One spot could be fine, and 20ft away could be a dangerous wind slab.  Watch for clues such as blowing snow, cornice formation and wind ridges to let you know where these slabs may exist.  Shooting cracks from your skis is a sign that snow is unstable and that steeper slopes should be avoided.  If in doubt, play it safe and stay away from steep slopes where new wind slabs could exist.  

Firm conditions exist under this small amount of new snow, making a fall even more consequential! 

advisory discussion

This is the kind of day where an avalanche accident is more likely to happen over a day where a foot or two of new snow falls.  One to two feet of snow is an obvious indicator to most people that unstable slopes are widespread, and people tend to be conservative in their decision making and stay off of steep slopes.  3-5” of new snow with winds however doesn’t create such widespread avalanche danger.  Avalanche danger is confined to deposition areas, which can be very variable in distribution.  It is easy to get lured out onto steep slopes because the snow that has been encountered so far seems fine and safe, only to unexpectedly hit a sensitive wind deposit and get caught in an avalanche.  Keep this in mind when you are making your decisions today, and don’t just rely on luck. 

Besides avalanches, a thin sharky snowpack with lots of early season obstacles exist!     

recent observations
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Recent observations reporting widespread firm conditions! Challenging for travel and riding, and concerning as a bed surface for avalanches to fail on.   

12/16 - Mammoth - Sherwins(Mammoth Rock): Thin coverage and poor condiitons.

12/16 - VA Lakes - South Peak: Thin firm windboard and snow depth.

12/16 - Rock Creek - Mt. Dade: Firm condiitons

Weather and CURRENT CONDITIONS
weather summary

A low-pressure system is moving thru the region this morning, bringing snow and moderate to strong SW winds.  While the system has moved in slowly, it will be quick to exit.  Snow began around 2am, and ~3-5” are expected before conditions dry up later this morning.  SW winds will decrease and some sun should make its way thru the clouds in the afternoon, with high temperatures reaching the low 30s around 10,000’.    

Breezy SW to W winds will continue for Tuesday, with above average temperatures reaching 40deg around 10,000’, and partly sunny skies.  The rest of the week should be dry and breezy with well above average temperatures. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy then becoming partly cloudy. Snow showers in the morning. Snow levels below 7000 feet. Chance of precipitation is 85%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%. Partly cloudy.
Temperatures: 32 to 37. deg. F. 18 to 23. deg. F. 40 to 45. deg. F.
Mid Slope Winds: Southwest 10 to 15 mph. Gusts up to 60 mph decreasing to 40 mph in the afternoon. Light winds. Light winds. Gusts up to 30 mph increasing to 45 mph in the afternoon.
Expected snowfall: 80% probability 2 to 4 inches. 20% probability of up to 2 inches. | SWE = up to 0.15 inch. in. 0 in. 0 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy then becoming partly cloudy. Snow showers in the morning. Snow levels below 7000 feet. Chance of precipitation is 95%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%. Partly cloudy.
Temperatures: 27 to 32. deg. F. 16 to 21. deg. F. 36 to 41. deg. F.
Ridge Top Winds: Southwest 30 to 45 mph with gusts to 75 mph decreasing to 20 to 30 mph with gusts to 50 mph in the afternoon. Southwest 10 to 15 mph with gusts to 25 mph. West 15 to 25 mph with gusts to 40 mph increasing to 20 to 35 mph with gusts to 60 mph in the afternoon.
Expected snowfall: 80% probability 2 to 4 inches. 20% probability of up to 2 inches. | SWE = up to 0.25 inch. 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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