Avalanche Advisory: Sunday - Dec 27, 2020

THIS AVALANCHE ADVISORY EXPIRED ON December 28, 2020 @ 7:00 am
Avalanche Advisory published on December 27, 2020 @ 7:00 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

A few inches of new snow and extreme SW winds yesterday will put small WIND SLABS at the top of the list for avalanche concerns today at all elevations on NW-NE-SE facing slopes. The tricky PERSISTENT SLAB avalanche problem remains a concern as well at all elevations on shady aspects.  MODERATE avalanche danger exists at and above treeline, and while LOW exists below treeline, it certainly does not mean NO.  And be wary of all the obstacles!     

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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2-4” of new snow fell between Friday night and Saturday morning with extreme SW winds at all elevations.  Winds dropped off dramatically as they shifted out of the NE and E around noon yesterday and are expected to stay relatively light today.  Be on the lookout for sporadic dense wind deposits on the leeward side of terrain features and sidewalls of gullies on steep slopes that may still be sensitive to a human trigger.  While an avalanche at higher elevations could be more consequential, an avalanche at any elevation could likely result in injury due to all the obstacles that exist in our shallow snowpack.  

Avalanche Problem 2: Persistent Slab
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The one thing consistently found across our forecast region is a weak snowpack on shady aspects (NW-NE-E) where early season November snow sits sugary at the base.  Whoomphing and shooting cracks continue to be reported, and propagating test results are widespread.  Where the right combination exists of overlying slab on a steep enough slope, lack of underlying anchors, and a sweet trigger spot, a human triggered avalanche could be possible that could break above you.  Triggering a smaller wind slab could be the extra force needed to step down and result in a larger than expected persistent slab avalanche. Be wary of steep shady terrain.   

advisory discussion

The snowpack is thin out there.  South of Mammoth it takes quite some effort, motivation, and a degree of masochism to travel in the mountains right now.  Mammoth and north travel is more realistic, but tons of obstacles, both visible and just under the surface, litter slopes.  Keep the speeds down and be careful!

recent observations
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-12/26 – VA Lakes: Small Windslab Avalanche triggered, weak snowpack, propagating test results.

-12/26 – Mammoth – Sherwins: Wind deposits including at lower elevations, whoomphing and shooting cracks, weak shallow snowack with propagating test results.

-12/26 – Mammoth Lakes Basin – Red Cone: ECTP

-12/26 – Mammoth Lakes Basin – Lake Mary Ridge: Whoomphing, propagating test results.

-12/26 – Mammoth Lakes Basin – Red Cone: Strong wind effects, ECTPs at multiple depths.   

-12/25 – Mammoth – Smugglers: Strengthening snowpack on East aspect below treeline.

Weather and CURRENT CONDITIONS
weather summary

Another cold storm system moves in from the Pacific today bringing cloudy skies and light snowfall of up to 2” mostly in the afternoon.  Temperatures will only reach the mid-teens around 10,000’ with light lower elevation winds and ridgetops gusts up to 30mph out of the south.  Snowfall will continue thru tonight and tomorrow with slightly greater amounts of accumulation likely.  The pattern continues to be active into the New Year with fast moving storms beginning with another chance of light snow 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: Cloudy. Chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 40%. Cloudy. Periods of snow.. Snow levels below 7000 feet. Chance of precipitation is 80%. Cloudy. Snow in the morning, then snow likely in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 100%.
Temperatures: 23 to 29. deg. F. 14 to 20. deg. F. 20 to 26. deg. F.
Mid Slope Winds: Light winds. Light winds. Light winds.
Expected snowfall: Up to 2 inches. | SWE = less than 0.10 inch. in. 70% probability of 1 to 3 inches. 30% probability of 3 to 6 inches. | SWE = up to 0.20 inch. in. 80% probability of 1 to 3 inches. 20% probability of 3 to 5 inches. | SWE = up to 0.20 inch. in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Cloudy. Chance of snow through the day. Snow levels below 7000 feet. Chance of precipitation is 50%. Cloudy. Snow likely. Snow levels below 7000 feet. Chance of precipitation is 90%. Cloudy. Snow in the morning, then snow likely in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 100%.
Temperatures: 16 to 22. deg. F. 9 to 14. deg. F. 13 to 19. deg. F.
Ridge Top Winds: South 15 to 20 mph with gusts to 30 mph. South 15 to 20 mph with gusts to 30 mph. West around 15 mph with gusts to 30 mph.
Expected snowfall: Up to 2 inches. | SWE = less than 0.10 inch. in. 70% probability of 2 to 4 inches. 30% probability of 4 to 6 inches. | SWE = up to 0.30 inch. in. 80% probability of 1 to 3 inches. 20% probability of 3 to 5 inches. | SWE = up to 0.20 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 Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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