Eastern Sierra Avalanche Forecast - 4/16/14

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THIS AVALANCHE ADVISORY EXPIRED ON April 17, 2014 @ 7:03 am
Avalanche Advisory published on April 16, 2014 @ 7:03 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is MODERATE.  This morning, the avalanche danger is LOW but by mid day, wet avalanches will be possible in steep, sunny, alpine  terrain as  sunshine softens and melts the snow surface. Avalanche conditions will change rapidly with the influence of warming or sun so plan to be off slopes by early afternoon. 

The avalanche danger rating is MODERATE in steep north facing alpine terrain in the Rock Creek area where depth hoar continues to react in propagation tests. On Friday, the Tioga Pass area will be covered in upcoming avalanche advisories.

 

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Bottom Line

The avalanche danger is MODERATE.  This morning, the avalanche danger is LOW but by mid day, wet avalanches will be possible in steep, sunny, alpine  terrain as  sunshine softens and melts the snow surface. Avalanche conditions will change rapidly with the influence of warming or sun so plan to be off slopes by early afternoon. 

The avalanche danger rating is MODERATE in steep north facing alpine terrain in the Rock Creek area where depth hoar continues to react in propagation tests. On Friday, the Tioga Pass area will be covered in upcoming avalanche advisories.

 

  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Wet
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Sunny skies and the sun's strong energy will quickly wet the snow surface on east to southeast high elevation slopes today. After a warm night, and a poor overnight freeze, the sun will melt the snow quickly today, breaking bonds and creating wet soggy areas especially on southeast to east and even northeast aspects today. High elevation slopes have winter snow but wet snow prevails below about 10,000 ft even on north aspects. Signs of increasing avalanche danger include sinking past your boot tops in moist snow and having large pinwheels roll downhill. 

Avalanche Problem 2: Persistent Slab
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The thick layer of depth hoar that has persisted all winter is still causing stability problems in the Rock Creek area. An observer over the weekend reported propagation in several ECT's on a northeast slope at 11,000 ft on the Tamarack Bench in Rock Creek. The bottom layer is still dry and fist hardness but the overlying slab is becoming more dense. With continued sun, eventually melt water will reach the buried weak snow and it will rapidly lose strength. It takes alot longer than we think for melt water to percolate down through the snowpack and affect more deeply buried layers, even in a shallow snowpack of less than 3 feet. 

advisory discussion

Temperatures this morning are about the same as yesterday morning--right around freezing--so the overnight freeze was thin and the snow will heat up by mid morning.  

The deeper snowpacks in the Mammoth and June Mountain areas is fairly stable in the thicker snowpack areas but thinner snowpack areas may see some wet slab avalanche activity today. Also, cornices have been getting very soft and even though they are not very big this year, it's not a good idea to linger below them because they tend to calve off randomly in the heat of the afternoon.

 

recent observations

There was no wet snow activity reported yesterday from the Rock Creek and Mammoth area yesterday.  A party skiing under Mt Abbott in Rock Creek reported snow depths of over 230 cm or over 7 ft of snow. Probing found a thick depth hoar layer near the ground. An ECT at 12,000 ft produced a fracture 42 cm down but did not propagate in the storm snow that fell at the end of March.  Areas of thick wind slab alternated with soft rippled snow on NE slopes. 

Bottomless snow was reported up to 11,000 ft on the Tamarack Bench in Rock Creek. 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 31 deg. F.
Max. temperature in the last 24 hours: 52 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 20 mph
Maximum wind gust in the last 24 hours: 36 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 29 inches
weather

Morning lows are in the 30's at the 9,000 ft. elevations this morning. Today will be sunny with light west and southwest winds blowing 20-25 mph along the ridgetops.  By tomorrow, the chance of rain and snow and thunderstorms increase in the afternoon. Unsettled cloudy weather with chances of rain and snow will continue through the upcoming weekend. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: Sunny mostly clear chance of showers
Temperatures: 54 deg. F. 35 deg. F. 54 deg. F.
Wind direction: West North South
Wind speed: 5-10 5 5
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: Sunny mostly clear chance of rain/snow
Temperatures: 52 deg. F. 29 deg. F. 52 deg. F.
Wind direction: west north South
Wind speed: 10-20 5 5
Expected snowfall: 0 in. 0 in. Trace to 1" in.
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