Avalanche Advisory: Monday - Jan 21, 2019

THIS AVALANCHE ADVISORY EXPIRED ON January 22, 2019 @ 6:50 am
Avalanche Advisory published on January 21, 2019 @ 6:50 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

The avalanche danger is CONSIDERABLE at all elevations today. High winds with 8-10” of new snow with addtitional accumulations throughout the day will form sensitive wind and storm slabs throughout the range. Persistent slab avalanches also remain an avalanche problem today.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Strong to Extreme SW-WSW winds blew consistently all night. These winds combined with moist snowfall (8-10”) that fell in sheltered areas with deeper totals in leeward zones will produce widespread wind slabs. WSW winds will continue at moderate to strong speeds and will back to the NW in the afternoon. Pay particular attention to the Notherly and Easterly aspects, but with potential changing wind directions evaluate all slopes with concern today. Expect to find fresh, sensitive wind slabs and cornices in mid to upper elevations where terrain is capturing windblown snow, and watch out for fat-looking wind pillows, cornice growth, and other wind-loaded features.

 

Avalanche Problem 2: Persistent Slab
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Our persistent slab problem is well established throughout the area with weak faceted snow present on a majority of aspects and elevations. Last week’s big storm and avalanche cycle cleaned out a lot of areas particularly in the alpine with mid-storm avalanches, but interestingly and important to note it also caused large avalanches in popular backcountry ski destinations below treeline (see 1/19 Observation “Large Natural Avalanche in “the Perch”). The big storm and its hefty weight did not in any way remove the persistent slab problem 100% from our forecast zone. Warm temperatures and the high water content of the big storm have formed a fat cohesive slab that resides above old snow with weak structure. Another persistent weak layer of concern is buried SURFACE HOAR which was widespread in the area; these feathery vertical crystals can surprisingly hold up a lot of weight and persist for long periods of time (See 1/20 Mammoth Rock Buried Surface Hoar Ob). Persistent slabs have been referred to as "sleeping dragons", and can remain dormant until a trigger wakes them up. Triggers in the form of a skier or an additional sliding storm/wind slab avalanche that impacts the weak area with added weight can cause the persistent slab to step down to the weak interface hidden below. Avalanches of this nature can propagate over wide distances and run through terrain which is often considered "safe."

Avalanche Problem 3: Storm Slab
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Be on the lookout today for instabilities such as shooting cracks, audible whumpfing, and recent avalanche activity. Be wary of any slope over 30 degrees, especially in relation to terrain traps such as gullies, depressions, and exposure to cliffs.

 

advisory discussion

It’s great that we are getting more snow, but don’t let today’s fresh blanket lull you into complacency. There have been multiple near misses potentially linked to our persistent slab problems (See 1/20 Skier triggered avalanche in Tele Bowls) & (See 1/20 Skier triggered avalanche in Lundy Canyon) the past few days with skiers/riders triggering significant avalanches and evidence of large natural avalanches that occurred during last week’s big storm. It will be a good day to be conservative and use proper route finding to minimize your exposure to potential hazards. Avoiding unsupported slopes, convex rolls, and riding above or near terrain traps are some basics to keep in mind.

recent observations
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1/20-Mammoth Area-Tele Bowls-Skier Triggered Avalanche

1/20-Lee Vining-Lundy Canyon-Skier Triggered Avalanche

1/20-Rock creek-Collapsing and Shooting Cracks

1/20-Mammoth Area-Surface Hoar near Mammoth Rock

1/20-Bishop/Buttermilks Area-Basin Mtn snow conditions

1/19-Mammoth Area-“The Perch”-Large Natural Avalanche

1/19-Bishop Creek-Bishop Bowl- Avalanche Activity

Weather and CURRENT CONDITIONS
weather summary

Snow showers are expected to continue today with a gradual breaking of the storm throughout the afternoon into tonight. 2” of new snow are expected to fall today. Temperatures will be nice and cold, so bundle up and be ready for temps in the 13-19F range in the higher elevations above 10,000ft and 20’s in the middle elevations. Winds will remain strong from the W-SW backing to the NW in the afternoon with gusts reaching 75mph at ridge top. Clearing conditions are expected for tonight with cold conditions (6-11F) and lessening winds. Temperatures will rebound after the current cold front moves through and there will be a break in storms expected through next weekend.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy then becoming partly cloudy. Chance of snow showers. Chance of precipitation is 45%. Partly cloudy then becoming clear. Slight chance of snow showers in the evening. Chance of precipitation is 15%. Sunny
Temperatures: 21 to 27. deg. F. 6 to 11. deg. F. 30 to 35. deg. F.
Mid Slope Winds: West 15 to 30 mph with gusts to 60 mph. Northwest 15 to 25 mph with gusts to 50 mph. Northwest 10 to 15 mph with gusts to 50 mph in the morning becoming light.
Expected snowfall: 2 in. 0 in. 0 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy then becoming partly cloudy. Chance of snow showers. Chance of precipitation is 50%. Partly cloudy then becoming clear. Slight chance of snow showers in the evening. Chance of precipitation is 10%. Sunny
Temperatures: 13 to 19. deg. F. 2 to 7. deg. F. 27 to 32. deg. F.
Ridge Top Winds: West 30 to 45 mph with gusts to 75 mph becoming northwest 20 to 30 mph with gusts to 50 mph in the afternoon. North 25 to 35 mph increasing to 30 to 45 mph after midnight. Gusts up to 75 mph. North 30 to 45 mph with gusts to 75 mph decreasing to 20 to 30 mph with gusts to 50 mph in the afternoon.
Expected snowfall: 2 in. 0 in. 0 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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