Avalanche Advisory: Tuesday - Dec 22, 2020

THIS AVALANCHE ADVISORY EXPIRED ON December 23, 2020 @ 6:57 am
Avalanche Advisory published on December 22, 2020 @ 6:57 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

SW winds picked up dramatically overnight blowing old surface snow into fresh dense deposits on the leeward side of terrain features where it’s possible that a human could trigger a Wind Slab avalanche.  Weak sugary snow persists at the base of the snowpack in many areas, and where the right combination of overlying slab thickness and lack of slope anchors exist a Persistent Slab avalanche could be triggered. MODERATE avalanche danger exists at all elevations, and barely covered obstacles are plentiful.   

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    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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Very strong gusty SW winds picked up dramatically overnight at all elevations reaching speeds into the 90mph range over ridgetops, and are expected to decrease slightly thru today and be more out of the W.  Be on the lookout for new dense freshly deposited wind slabs on the leeward side of ridges and cross-slope features and sidewalls of gullies especially on NW-NE-S facing aspects.  The strength of the winds could cause slabs to form in unexpected places and further downslope than usual.  Use cornice formation and blowing snow as clues for places to avoid. Even a small slide can be consequential with all the exposed obstacles of our thin snowpack right now.  

Avalanche Problem 2: Persistent Slab
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Shooting cracks, whoomphing, and propagating test results continue to be reported and are concerning signs that the sugary faceted snow “persisting” at the base of the snowpack is weak. It’s most possible to trigger a persistent slab avalanche on a steep slope without adequate rocks and bushes protruding thru the weak layer to keep it anchored in place. Our thin variable snow coverage will keep these avalanches small and isolated, but triggering even a small pocket could result in injury or worse, especially as these types of avalanches tend to fail above the trigger. E-N-NW aspects are the most concerning, and all elevations are suspect. Take your shovel out and explore the snow yourself, and avoid steep consequential slopes where the right combination of buried weak layers and lack of anchors may exist.

advisory discussion

The one thing that is consistent throughout the forecast region is a thin snowpack. What varies is just how thin. The Mammoth area has the deepest snowpack with the best chances of linking a few turns together without hitting a rock or a log, with those chances decreasing north toward VA Lakes, and tennis shoes being better travel tools than skis in the southern mountains above Bishop. The catch here is that the places with the most snow are also the places with a better chance of triggering an avalanche. Early season snow in November sat around for nearly a month turning into weaker and weaker faceted snow until it became buried by December’s snowfall.  The shallow snowpack with the plentitude of obstacles will make it hard to get into dangerous terrain, but not impossible.  Best to keep it mellow by keeping your speed down and sticking to lower angle terrain, and keep monitoring the snow pack for when more snow comes. 

Weather and CURRENT CONDITIONS
weather summary

A cold front moving thru the region has brought strong gusty winds out of the SW overnight which will decrease slightly and shift out of the W thru today.  Expect sunny skies with highs in the mid 30s around 10,000’.  Dry conditions will prevail thru Christmas Eve, and then unsettled weather is expected for Christmas day thru the weekend with some snowfall but no major accumulations.  

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny. Snow levels below 7000 feet. Chance of precipitation is 10%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 35 to 41. deg. F. 11 to 16. deg. F. 34 to 39. deg. F.
Mid Slope Winds: West 15 to 20 mph. Gusts up to 65 mph decreasing to 45 mph in the afternoon. Northwest around 15 mph. Gusts up to 45 mph decreasing to 30 mph after midnight. West around 15 mph in the morning becoming light. Gusts up to 35 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny. Snow levels below 7000 feet. Chance of precipitation is 10%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 29 to 35. deg. F. 9 to 14. deg. F. 32 to 38. deg. F.
Ridge Top Winds: West 30 to 50 mph with gusts to 90 mph decreasing to 20 to 35 mph with gusts to 65 mph in the afternoon. Northwest 15 to 30 mph. Gusts up to 60 mph decreasing to 40 mph after midnight. East 15 to 30 mph with gusts to 45 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. 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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