Avalanche Advisory: Thursday - Jan 17, 2019

THIS AVALANCHE ADVISORY EXPIRED ON January 18, 2019 @ 7:00 am
Avalanche Advisory published on January 17, 2019 @ 7:00 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

HIGH avalanche danger will be widespread today due to intense snowfall and extreme SW winds. Wind Slab, Storm Slabs, and Persistent Slab problems all exist.  Travel in or below avalanche terrain NOT RECOMMENDED!

4. High

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Above Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Near Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Below Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
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Heavy dense snow fell throughout last night and will continue thru today with strong to extreme SW winds.  Over the last 12 hours snow fell with nearly 3” of water content on Mammoth Mtn, and ridgetop wind speeds reached over 160mph overnight. Another 1-2.5’+ of snow is expected throughout today with continued very strong SW winds.  Fresh wind slabs will be very large and sensitive.  Large to very large natural and human triggered wind slab avalanches will be VERY likely, if not certain.  With the extreme winds and intense amounts of snowfall treat all slopes as potentially wind loaded and sensitive, and avoid being on or under slopes greater than 30 degrees.  

Avalanche Problem 2: Storm Slab
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Heavy dense snowfall last night will continue through today at rates that are faster than the snowpack is able to adjust for even in areas sheltered from the wind.  Natural and human triggered storm slab avalanches will be very likely today.  To add to the problem fragile surface hoar was found buried just under the new snow yesterday in several sheltered locations.  Where this exists, slopes will be even more sensitive. Avoid being on or under slopes greater than 30 degrees. 

Avalanche Problem 3: Persistent Slab
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Prior to this storm layers of loose weak faceted snow have been found buried deeper down in the snowpack throughout the forecast region.  With last night’s and today’s intense loading, it is now likely that very large, destructive and deadly avalanches could fail on these deeper weak layers resulting in slides spanning far across slopes and running far into run-out zones.  Smaller wind slab or storm slab avalanches could likely step-down and be the trigger for a persistent slab avalanche.   Stay well away from even the bottom of slopes today.

advisory discussion

We are in the middle of the biggest storm of the season.  This storm is centered on Mammoth, and while north and south of Mammoth will receive lesser amounts of snow, they are still getting plenty to reach HIGH avalanche danger.  The most intense loading occurred last night, with 3-4” an hour pounding down at times.  A slight lull is expected this morning before intensity picks up again with rates of 2” an hour likely this afternoon.  The one good thing is that the snow will gradually become less dense as the day progresses, but don’t let this right-side-up structure fool you. Snow will still be falling faster than it has time to stabilize.  It is best to simply avoid being on or under avalanche terrain today. 

Weather and CURRENT CONDITIONS
weather summary

Heavy snow will continue throughout today, with 1.5-2+’ of additional snow expected before tapering off late tonight.  Extreme SW winds will continue with ridge top gusts well over 100mph, and again reaching upwards of 125mph this afternoon.  Snow levels will drop throughout the day to below 5000’ tonight. Strong winds will continue tomorrow out of the west with cloudy skies and a possibility of some sunshine. Another cold front is expected for Sunday bringing much more modest amounts of snowfall. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Widespread snow showers. Snow levels below 7000 feet. Chance of precipitation is 100%. Mostly cloudy. Widespread snow showers in the evening, then slight chance of snow showers after midnight. Snow levels below 7000 feet. Chance of precipitation is 60%. Mostly cloudy then becoming partly cloudy. Slight chance of snow. Snow levels below 7000 feet. Chance of precipitation is 15%.
Temperatures: 26 to 34. deg. F. 15 to 20. deg. F. 31 to 36. deg. F.
Mid Slope Winds: Southwest 25 to 35 mph with gusts to 75 mph. Southwest 25 to 40 mph with gusts to 65 mph. West 10 to 15 mph with gusts to 60 mph.
Expected snowfall: 80% probability of 12 to 24 inches. 20% probability of 24 to 36 inches. | SWE = up to 1.20 inches. in. 60% probability of 2 to 6 inches. 40% probability of 6 to 10 inches. | SWE = up to 0.25 inch. in. trace in.
Over 10,000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Widespread snow showers. Snow levels below 7000 feet. Chance of precipitation is 100%. Mostly cloudy. Widespread snow showers in the evening, then slight chance of snow showers after midnight. Snow levels below 7000 feet. Chance of precipitation is 90%. Mostly cloudy then becoming partly cloudy. Slight chance of snow. Snow levels below 7000 feet. Chance of precipitation is 20%.
Temperatures: 19 to 24. deg. F. 10 to 15. deg. F. 26 to 31. deg. F.
Ridge Top Winds: Southwest 55 to 75 mph. Gusts up to 105 mph increasing to 125 mph in the afternoon. Southwest 60 to 75 mph with gusts to 125 mph becoming west and decreasing to 40 to 55 mph with gusts to 80 mph after midnight. West 30 to 50 mph with gusts to 80 mph.
Expected snowfall: 80% probability of 16 to 24 inches. 20% probability of 24 to 30 inches. | SWE = 1.05-1.55 inches. in. 60% probability of 2 to 6 inches. 40% probability of 5 to 9 inches. | SWE = up to 0.30 inch. in. trace 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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