Avalanche Advisory: Sunday - Jan 26, 2020

THIS AVALANCHE ADVISORY EXPIRED ON January 27, 2020 @ 6:52 am
Avalanche Advisory published on January 26, 2020 @ 6:52 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

Moderate avalanche danger exists at Upper and Middle Elevations on Northerly-Easterly aspects for fresh Wind Slab.  Southerly winds with fresh snow will develop new Wind slab in leeward catchment zones.

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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Shallow, fresh wind slab will develop with today's new snowfall and southerly winds.  Northerly-Easterly aspects at Upper to Middle elevations will be of most concern. New snow will be falling and deposited on a variety of slick surfaces from wind shorn old slab to sheeny sun kissed panels.  Identify features of concern, such as fat pillows adjacent to ridgeline, rock outcroppings or cliff bands and avoid riding over terrain traps. Although unlikely, triggering a fresh wind slab today may add enough weight to cause reaction in residing weak persistent slab conditions within the old snow and cause an avalanche to “step down” and produce a larger more destructive avalanche.

Avalanche Problem 2: Persistent Slab
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Large collapses, surface cracking and propagating test results have been observed throughout the range within our relative thin and degrading snowpack. A majority of these signs of poor stability are attributed to loose faceted snow residing under buried crusts or old wind board layers within the upper part of the snowpack. There has been no avalanches reported on these buried weak layers, but it is a present and real condition that should be considered in making wise terrain choices.  Distribution is inconsistent and is isolated to slopes with poor snowpack structure and areas where there is contiguous slab. Cross loaded gullies within thin vegetated areas, for example, have been zones where this condition has been found. Persistent slabs can be much more unpredictable than new snow storm or wind slabs and can be triggered from a distance and propagate over further distances in unpredictable patterns.

advisory discussion

New snow instabilities should be the backcountry user’s focus today. Thin conditions, very firm surfaces and a plethora of obstacles that may be recently disguised are the main hazards out there right now. Evaluate what may be lurking just beneath a new pasting of snow before committing to dropping in. Along with fresh wind slab and loose dry concerns the ongoing existence of Persistent slab conditions should be also be considered. Although unlikely, the possibility of larger avalanches in isolated terrain should keep us a bit wary, especially with the addition of new snow load.  A variety of crust/facet combos are present within the upper part of the snowpack and weaker loose snow can be found around most rocky and vegetated areas. A small new snow point release or wind slab that gains volume down slope may add just enough weight to tip the scales in some isolated areas. The uncertainty and lack of confidence with these underlying weaknesses possibly being reactive to skier triggers or added snow load are the factors contributing to listing Persistent Slab as an Avalanche Problem. Thin conditions and clear nights have continued to drive temperature gradients further weakening residing snowfields and producing conditions more typically found in the continental climates such as Colorado.

Weather and CURRENT CONDITIONS
weather summary

Snow has hit the area this morning and will continue with scattered flurries through the afternoon. 1-4” are possible across the mountains primarily falling in the early part of the day.  SW winds with velocities (30-55mph) and gusts reaching 70mph at higher elevations will accompany this weak, quick moving storm. Winds speeds as well as snow fall are expected to decrease this afternoon as the system departs the area. Temperatures will hover just below freezing at higher elevations while below 10000ft could still reach 41F. A clear night and backing NW winds are slated to follow with return to sunny skies Monday. There is a slight chance of precipitation hitting the area Tuesday, but looks to be staying north at this point.

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: Mostly cloudy. Snow in the morning, then scattered snow showers in the afternoon. Snow levels 8000 feet decreasing to below 7000 feet in the afternoon. Chance of precipitation is 95%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 31 to 41. deg. F. 19 to 25. deg. F. 33 to 43. deg. F.
Mid Slope Winds: Southwest to west 15 to 25 mph. Gusts up to 40 mph. West to northwest around 15 mph with gusts to 35 mph. Northwest around 10 mph.
Expected snowfall: 80% probability of 1 to 3 inches. 20% probability of 3 to 5 inches. | SWE = up to 0.30 inch. in. 0 in. 0 in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Snow in the morning, then scattered snow showers in the afternoon. Snow levels 8000 feet decreasing to below 7000 feet in the afternoon. Chance of precipitation is 100%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%.
Temperatures: 25 to 31. deg. F. 14 to 20. deg. F. 25 to 33. deg. F.
Ridge Top Winds: Southwest 30 to 55 mph with gusts to 70 mph becoming west 20 to 30 mph with gusts to 45 mph in the afternoon. Northwest 15 to 30 mph with gusts to 45 mph. Northwest 15 to 25 mph. Gusts up to 40 mph in the morning.
Expected snowfall: 80% probability of 2 to 4 inches. 20% probability of 4 to 6 inches. | SWE = up to 0.45 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 Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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