Avalanche Advisory: Saturday - Mar 21, 2020

THIS AVALANCHE ADVISORY EXPIRED ON March 22, 2020 @ 6:28 am
Avalanche Advisory published on March 21, 2020 @ 6:28 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

MODERATE avalanche danger at Upper and Middle elevations Saturday for PERSISTENT SLAB on NW-N-NE-E ASPECTS. LOW avalanche danger below tree line. Although there have not been any avalanches directly attributed to Persistent Slab problems, stability tests in the Mammoth area showing propagating results deserve attention. This condition is unpredictable and if triggered can potentially produce large, dangerous avalanches. Use wise terrain choice regarding this issue and avoid convex and unsupported slopes or riding above terrain traps. Human triggered avalanches are possible, so evaluate snow and terrain carefully today.

*Avalanche Danger will be most concerning around Mammoth Lakes and areas to the North 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: Persistent Slab
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
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    Historic
    Very Large
    Large
    Small

Our most recent storm deposited from 1-3’ of snow which is 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 weak layers. Recent stability tests and snow profiles highlight this poor structure. Although there has been no report of avalanches resulting from our Persistent Slab problem, these slides 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 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

The main hazard is the thin and shallow condition of the snowpack. This past storm has hidden a plethora of obstacles and there have been some serious injuries since the storm. This has not been the season, nor the time right now with unprecedented times in the modern world, to risk serious injury by skiing with abandon.

Weather and CURRENT CONDITIONS
weather summary

Cloudy conditions and light winds and a chance of light snow showers are on tap today with temperatures remaining around the freezing mark for lower elevations and in the teens to 20’s above 10000ft. There is a continued chance for light snow showers, a slight uptick in SW winds and partly cloudy conditions through the weekend.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy. Slight chance of snow showers in the morning, then scattered snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 35%. Mostly cloudy then becoming partly cloudy. Isolated snow showers in the evening. Snow levels below 7000 feet. Chance of precipitation is 20%. Partly cloudy. Slight chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 20%.
Temperatures: 28 to 36. deg. F. 15 to 21. deg. F. 32 to 40. deg. F.
Mid Slope Winds: Light winds. Light winds. Light winds.
Expected snowfall: 20% probability up to 2 inches. 80% probability no accumulation. | SWE = less than 0.10 inch. in. 10% probability up to 1 inch. 90% probability no accumulation. | SWE = less than 0.10 inch. in. 20% probability up to 1 inch. 80% probability no accumulation. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy. Slight chance of snow showers in the morning, then scattered snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 50%. Mostly cloudy then becoming partly cloudy. Scattered snow showers in the evening. Snow levels below 7000 feet. Chance of precipitation is 25%. Partly cloudy. Chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 25%.
Temperatures: 19 to 27. deg. F. 9 to 14. deg. F. 23 to 31. deg. F.
Ridge Top Winds: Southeast around 15 mph. South around 15 mph. Gusts up to 25 mph in the evening. South around 15 mph. Gusts up to 25 mph in the morning.
Expected snowfall: 30% probability of 1 to 3 inches. 70% probability no accumulation. | SWE = up to 0.15 inch. in. 20% probability up to 1 inch. 80% probability no accumulation. | SWE = less than 0.10 inch. in. 30% probability up to 1 inch. 70% probability no accumulation. | 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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