Avalanche Advisory: Sunday - Dec 23, 2018

THIS AVALANCHE ADVISORY EXPIRED ON December 24, 2018 @ 6:49 am
Avalanche Advisory published on December 23, 2018 @ 6:49 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Natural and Human triggered avalanches will be unlikely today.  However, it will not be impossible for a human to trigger a small wind slab with lingering sensitivity in isolated high elevation areas in steep or extreme SE-E-N-NW facing terrain.  Tonight, for all you midnight headlamp tourers, human triggered avalanches will become slightly more possible in this same type of terrain as SW winds redistribute up to an inch of new snow into fresh small isolated wind slabs.  Early season obstacles exist!

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Below Treeline
Avalanche Problem 1: Wind Slab
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Small Isolated wind slabs formed on Friday at mid to upper elevations.  These formed due to strong SW ridgetop winds redistributing a few inches of fresh snow that fell Friday morning. Light winds yesterday halted the growth of these wind deposits and allowed them time to stabilize FOR THE MOST PART.  Today, there could still exist rare isolated small wind slabs still sensitive to human triggering.  Look out for the possibility of one of these dense pockets in steep or extreme upper elevation SE-E-N-NW facing terrain, on the leeward side of ridges or the sidewalls of gullies.  With the possibility of up to an inch of new snow tonight accompanied by moderate SW winds, new small isolated wind slabs could form in the same types of areas.  While small, triggering one of these could lead to a nasty fall in complex terrain.  

As snowfall increases throughout the day on Christmas Eve, and especially late Christmas Eve night, with up to a foot of new snow in areas possible, avalanche danger will rise.

advisory discussion

While avalanche concern is small and very isolated at the moment, over the last several days more facets are being found in the underlying thin snowpack in many areas. While not very concerning right now, these faceted layers could act as a weak layer once significant additional snow is added.  While you are out it is not a bad idea to poke down in the snow, check out and feel the different layers and see what those underlying snow grains may be like. Are they starting to feel more sugary and loose?  Please let us know what you are finding out there!  

Weather and CURRENT CONDITIONS
weather summary

A weak disturbance will make for cloudy skies today and a chance of flurries in the afternoon into tonight, with up to an inch of snow for the higher mountains possible before midnight.  Winds will be out of the west and southwest with moderate gusts into the 40s, and high temperatures reaching the mid 30s around 10,000’.  

A stronger storm will move in Christmas Eve, with snowfall picking up in the afternoon and especially late at night.  Up to a foot of new snow is expected for the higher mountains by Christmas morning.  SW winds will be on the increase right along with snowfall intensity. 

Cold temperatures are expected for Christmas day and the rest of the week, with unstable flow that could bring more light snow towards the end of the week. 

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. Slight chance of snow in the afternoon. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 10%. Mostly cloudy then becoming partly cloudy. Slight chance of snow in the evening. Snow levels 7000 feet decreasing to below 7000 feet after midnight. Chance of precipitation is 15%. Partly cloudy then becoming mostly cloudy. Chance of snow through the day. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 50%.
Temperatures: 36 to 42. deg. F. 22 to 27. deg. F. 35 to 41. deg. F.
Mid Slope Winds: Southwest 10 to 15 mph with gusts to 40 mph. West 15 to 20 mph with gusts to 45 mph. Southwest 15 to 25 mph. Gusts up to 35 mph increasing to 50 mph in the afternoon.
Expected snowfall: none in. Up to 1 inch. | SWE = less than 0.10 inch. in. 80% probability up to 2 inches. 20% probability of 2 to 3 inches. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Slight chance of snow in the afternoon. Snow levels below 7000 feet increasing to 7500 feet in the afternoon. Chance of precipitation is 20%. Mostly cloudy then becoming partly cloudy. Slight chance of snow in the evening. Snow levels 7000 feet. Chance of precipitation is 20%. Partly cloudy then becoming mostly cloudy. Chance of snow through the day. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 50%.
Temperatures: 30 to 35. deg. F. 18 to 23. deg. F. 28 to 33. deg. F.
Ridge Top Winds: West 15 to 30 mph with gusts to 45 mph. West 25 to 40 mph decreasing to 20 to 30 mph after midnight. Gusts up to 60 mph. West 20 to 35 mph. Gusts up to 45 mph increasing to 60 mph in the afternoon.
Expected snowfall: none in. Up to 1 inch. | SWE = less than 0.10 inch. in. 80% probability up to 2 inches. 20% probability of 2 to 3 inches. | 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 Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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