Avalanche Advisory: Monday - Jan 27, 2020

THIS AVALANCHE ADVISORY EXPIRED ON January 28, 2020 @ 6:35 am
Avalanche Advisory published on January 27, 2020 @ 6:35 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

Moderate avalanche danger exists at Upper and Middle Elevations on N-E-S aspects for fresh Wind Slab. West to NW winds will transport fresh snow to leeward terrain conducive to capturing snow. Identify features of concern for heightened avalanche conditions today.

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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Look out for fresh wind slab and new snow deposits after yesterday's light snow accumulations (1-4”). SW-Westerly winds were actively transporting snow Sunday and continued blowing at optimal loading velocities last night. Northerly-Easterly aspects at Upper to Middle elevations will be of most concern, but with the Westerly oriented winds and potential NW winds today, don’t be surprised to find some Southerly aspects cross loaded with new snow. 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. While there have been no avalanches reported on these buried weak layers, they should be considered when making terrain choices. Distribution is inconsistent and 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

1-4” of snow fell yesterday across the zone with westerly and southerly winds transporting it to a variety of leeward terrain. There were not any observations of cohesive or reactive wind slab yesterday, but that likely has changed overnight as the new snow settles, bonds and has continued to be blown around across the landscape. Fresh wind slabs will likely be shallow and not significant in volume, but as always could present some hazard in exposed or extreme terrain. There is also some potential for small loose dry sloughing and should be noted if riding in confined terrain or on unsupported slopes over exposure. Thin conditions, very firm surfaces and shallowly-buried obstacles will be 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.

Weather and CURRENT CONDITIONS
weather summary

Moderate West to Northwesterly winds with partly cloudy conditions for today. Mild temperatures persist with 26-34F on tap for elevations above 10000ft and up to 43F possible in the lower mountains. The fast moving wave Tuesday looks to be heading north, but a slight chance of precipitation for the area is not out of the question. Another ridge of high pressure will be moving into the area late this week bringing possible record highs for the start of February.

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: Partly cloudy. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%. Partly cloudy then becoming clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 33 to 43. deg. F. 23 to 29. deg. F. 34 to 44. deg. F.
Mid Slope Winds: West to northwest 10 to 20 mph. Gusts up to 30 mph. West around 15 mph. Gusts up to 35 mph. Southwest around 15 mph with gusts to 45 mph.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%. Partly cloudy then becoming clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 26 to 34. deg. F. 18 to 24. deg. F. 26 to 34. deg. F.
Ridge Top Winds: West 15 to 25 mph with gusts to 40 mph. West 15 to 30 mph. Gusts up to 45 mph. Southwest 20 to 35 mph with gusts to 55 mph.
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 Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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