Avalanche Advisory: Friday - Mar 20, 2020

THIS AVALANCHE ADVISORY EXPIRED ON March 21, 2020 @ 6:50 am
Avalanche Advisory published on March 20, 2020 @ 6:50 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

MODERATE avalanche danger exists at Upper and Middle elevations Friday for WIND SLAB on NORTHERLY-EASTERLY ASPECTS. LOW avalanche danger remains below tree line. Although unlikely, Persistent Slab avalanches remain a concern on NW-N-NE-E aspects at upper-mid elevations. Be observant for drifts or fat deposits of snow on convex and unsupported slopes, couloirs, and areas adjacent to ridgeline, cliff bands and rock outcroppings. Human triggered avalanches are possible, so evaluate snow and terrain carefully and focus on features of concern.

*Avalanche Danger will be most concerning around Mammoth Lakes and areas to the North which received more snow than the southern reaches of the forecast area*

 

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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The Mammoth area is of most concern where 1-3’ of snow fell during our most significant storm since December. Be on the lookout for residing Wind Slab on NW-N-NE-E-SE aspects above and near tree line today. There has not been much reported post-storm activity of anything significant, but cold overnight temperatures and settlement of the new snow may produce some tension in areas that could be released by skier trigger. Namely be aware of convex or unsupported slopes where even a small slide could flush you into rocks or over exposure. Be observant for cornices, cross loaded drifts and pillows of snow established on terrain features such as slopes adjacent to ridgeline, cliff bands and convex rollovers. Shooting cracks or panels of firmer wind effected snow resting on top of looser, less cohesive snow will be good indicators that wind slab is present. Be observant of overhead hazards, and plan your route accordingly if you’re travelling in terrain where avalanches may impact you from above.  

Avalanche Problem 2: Persistent Slab
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Our most recent storm has deposited from 1-3’ of snow which is now rapidly settling and forming a denser more cohesive slab on top of our residing old, rotten, and incredibly variable snowpack. NW-N-NE-E aspects at Upper and particularly Middle Elevations are of most concern for Persistent Slab problems. The old snow which was deposited primarily in December is full of weak faceted snow, melt-freeze crusts and all sorts of nasty layers. Recent stability tests and snow profiles highlight this poor structure. Although unlikely and on the healing trend, our Persistent Slab problem can be hard to predict, could produce relatively large destructive avalanches, and possibly could propagate over wide areas. Take heed that we have a relatively weak snowpack compared to normal conditions for California and that taking the extra time to dig a pit and see what you’re dealing with may be eye opening. Many times persistent slabs are triggered by weighting adjacent shallow weak areas around rock outcroppings, trees or other obstacles that may have increased zones of rotten and faceted snow that collapse and aid in triggering a weak layer. Maintain good travel protocols, such as traveling on slopes one at a time (both up and down), anchoring up in safe spots, and maintaining good communication and consistent group plans and routes.

advisory discussion

A common thread for this entire season has been that the main hazard is thin and shallow conditions. This past storm was just enough to hide a lot of obstacles and there have been serious injuries already occurring in the Sherwins since the storm. I’ve said it before, but this is not the season nor the time to ski with abandon.

Weather and CURRENT CONDITIONS
weather summary

Partly cloudy conditions and light winds today with temperatures remaining around the freezing mark for lower elevations and in the teens to low 20’s above 10000ft. Isolated snow showers are possible in the afternoon. Continued chance for light snow showers, light winds and cloudy conditions for the next few days.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy. Isolated snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 20%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%. Partly cloudy then becoming mostly cloudy. Slight chance of snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 25%.
Temperatures: 26 to 34. deg. F. 12 to 18. deg. F. 30 to 38. deg. F.
Mid Slope Winds: Light winds. Light winds. Light winds.
Expected snowfall: 0 in. 0 in. Up to one inch. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy. Isolated snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 20%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%. Partly cloudy then becoming mostly cloudy. Chance of snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 25%.
Temperatures: 17 to 25. deg. F. 6 to 11. deg. F. 20 to 28. deg. F.
Ridge Top Winds: Light winds. Light winds. Southeast around 15 mph in the morning becoming light.
Expected snowfall: 0 in. 0 in. Up to one 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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