Avalanche Advisory: Wednesday - Dec 30, 2020

THIS AVALANCHE ADVISORY EXPIRED ON December 31, 2020 @ 6:32 am
Avalanche Advisory published on December 30, 2020 @ 6:32 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

MODERATE Avalanche danger exists today for fresh WIND SLAB above and near tree line on ALL ASPECTS today. Look for cross- loaded areas and fresh pillows adjacent to ridgeline, convexities and other terrain features conducive to capturing wind transported snow.  Remain cognizant of PERSISTENT SLAB conditions at all elevations on Northerly-Easterly terrain.  Evaluate your exposure to terrain traps or lurking obstacles where even a small human triggered avalanche could be consequential. Recent fresh snow is disguising a plethora of nasty obstacles just under the surface.

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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Fresh wind slabs will be possible to trigger on ALL ASPECTS today, primarily in the Upper elevations and near tree line. Northerly winds blew yesterday and will continue early today until an expected direction change switches back to the SW this afternoon. There is plenty of low density transportable snow from this past storm to be moved around especially since yesterday turned out to be quite calm except for the highest elevations.  Sensitive cross loaded wind slabs were reported from the Mammoth area in gully like terrain on a variety of aspects yesterday and expect more of the same today.  Human triggered wind slab avalanches will be possible in specific areas such as slopes adjacent to ridgeline, deposition zones under cliff bands, and steeper convex terrain such as rollovers and cross loaded gully features. Stay focused on your exposure to down slope hazards, terrain traps, and cliffs where even a small slide could prove to be hazardous if you were caught. There is a lot of exposed rock and other obstacles that even a small ride will be dangerous. Be on the lookout for fresh pillows of snow and fat looking drifts to gauge the distribution of fresh wind slab

Avalanche Problem 2: Persistent Slab
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Up to this point, a shallow, weak, and concerning snowpack structure exists in a majority of our northerly-easterly facing terrain at all elevations. Warm temperatures and time has helped much of the thin snowpack strengthen a bit through settlement, but overall, the basic weak upside down structure of a firmer slab above looser faceted November snow at the base remains.  Areas of most concern remain northerly-easterly slopes that held onto November snows and are now capped with the firmer slab from the few minimal storms we have had in December. Steeper slopes above 30degrees and above exposure or terrain traps are of most concern.  Persistent slabs may be remotely triggered from a distance and propagate over wide spaces of terrain. Triggering a fresh wind slab today may be just enough to cause a persistent slab to step down and cause a deeper more destructive avalanche.

advisory discussion

The Sunday evening - Monday storm added much needed snow to the forecast area, and slowly, but surely, we are adding bit by bit to the overall snowpack. Weather projections for the first week of 2021 continue to look promising for the jet stream to settle into a more zonal, westerly flow over California with moisture plumes setting up to hit the Sierra. It would be really beneficial to not only finally get a robust snowpack established, but also potentially initiate an avalanche cycle to clean up the residual weaknesses and upside down structure that exists throughout the zone. The key thing will be to manage the desire to ride with the timing of hopefully heavier, deeper accumulating storm systems that could tip the scale of our shallow and scabby existing Nov/Dec snowpack.

Weather and CURRENT CONDITIONS
weather summary

A cloudy day is on tap with warming temperatures above freezing for lower elevations and reaching 31F above 10000’. Light to moderate NW winds will continue for the early part of the day and transition back to a SW flow with ever increasing velocities and gusts reaching 50mph in the afternoon. A quick hitting storm will likely bring a couple of inches to the mountains with potentially more accumulation on the crest.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Mostly cloudy. Chance of snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 35%. Mostly cloudy then becoming partly cloudy. Chance of snow in the morning. Snow levels below 7000 feet. Chance of precipitation is 35%.
Temperatures: 32 to 38. deg. F. 15 to 20. deg. F. 23 to 29. deg. F.
Mid Slope Winds: Light winds. Southwest 15 to 25 mph with gusts to 65 mph. Northwest 15 to 35 mph. Gusts up to 60 mph decreasing to 40 mph in the afternoon.
Expected snowfall: 0 in. 80% probability up to 2 inches. 20% probability of 2 to 4 inches. | SWE = less than 0.10 inch. in. Up to 1 inch. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Mostly cloudy. Snow becoming likely after midnight. Snow levels below 7000 feet. Chance of precipitation is 80%. Mostly cloudy then becoming partly cloudy. Chance of snow in the morning. Snow levels below 7000 feet. Chance of precipitation is 50%.
Temperatures: 25 to 31. deg. F. 10 to 15. deg. F. 16 to 22. deg. F.
Ridge Top Winds: Northwest 15 to 25 mph. Gusts up to 35 mph increasing to 50 mph in the afternoon. West 25 to 35 mph with gusts to 60 mph increasing to southwest 35 to 50 mph with gusts to 80 mph after midnight. Northwest 30 to 45 mph shifting to the north 25 to 35 mph in the afternoon. Gusts up to 65 mph.
Expected snowfall: 0 in. 60% probability up to 2 inches. 40% probability of 2 to 4 inches. | SWE = less than 0.10 inch. in. Up to 1 inch. | SWE = less than 0.10 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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