Eastern Sierra Avalanche Forecast - 4/6/14

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THIS AVALANCHE ADVISORY EXPIRED ON April 7, 2014 @ 7:09 am
Avalanche Advisory published on April 6, 2014 @ 7:09 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is generally LOW this morning and will rise to MODERATE on slopes steeper than 35 degrees during the day with intense solar heating of the snow. 

Loose wet snow avalanches are possible today on SE-E and northerly aspects especially in the Mammoth Lakes Basin. Snow covered aspects facing south to west will warm also.

 

Today’s advisory is in memory of Walter Rosenthal, Scott McAndrews and James Juarez who died eight years ago today on April 6, 2006 in a tragic accident on Mammoth Mountain. WAlter Rosenthal was a friend to many and we miss his keen wit, extraordinary intellect and leadership abilities. 

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 generally LOW this morning and will rise to MODERATE on slopes steeper than 35 degrees during the day with intense solar heating of the snow. 

Loose wet snow avalanches are possible today on SE-E and northerly aspects especially in the Mammoth Lakes Basin. Snow covered aspects facing south to west will warm also.

 

Today’s advisory is in memory of Walter Rosenthal, Scott McAndrews and James Juarez who died eight years ago today on April 6, 2006 in a tragic accident on Mammoth Mountain. WAlter Rosenthal was a friend to many and we miss his keen wit, extraordinary intellect and leadership abilities. 

  • 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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Isolated wet loose avalanches will be possible on north through southeast facing slopes. Of course, aspects facing south and west that have snow cover will receive the full brunt of the sun's energy. It's April and even north facing slopes are exposed to more hours of direct sun. Yesterday, a small loose avalanche was observed on a NE aspect in alpine terrain in the Mammoth Lakes Basin.

This type of instability is dynamic - slopes may go from stable to unstable in 30 minutes or less. The recent storm snow can become unstable very quickly- wet surface snow and/or 'pin wheels' rolling down slopes are clear signs that the potential for wet avalanches is increasing and it's time to move to colder and less rocky slopes. New

Avalanche Problem 2: Persistent Slab
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The depth hoar layer in Rock Creek continues to collapse during stability tests. The layer is widespread above 10,000 ft on north facing aspects. The snowpack is  shallow, around 3 to 4 feet so triggering could be initiated by a single or multiple skiers on a slope. Triggering points will be where the snowpack is thin along the sides of gullies. Strong solar radiation that makes the snow surface noticeably denser or moister may also increase the sensitivity to triggering. A lack of avalanche activity is not a reliable indicator of potential hazard.

http://youtu.be/6L1pYYdJBSU

advisory discussion

One week ago, the most powerful storm of the winter dropped 1 to almost 2 feet of cold dry snow over the advisory area. The storm was unusual because winds were light and powder piled up without the curse of strong winds creating wind slabs. The main avalanche problem was loose sluffs and everyone enjoyed the best skiing in years.

All things change- after all, this is April. Over the next few days, the air mass will warm as high pressure builds. The sun’s energy is double what it was in January. Snow will transition from a cold winter snow pack to more spring like conditions. Mid elevations will take the brunt of the rapid warming today. I expect the number of loose wet slides to increase in alpine terrain , especially on east to southeast facing slopes.  

Rapid warming is one of the obvious signs of instability. When the snow pack is subject to a rapid warming, it can become very wet and unstable, increasing the stress on the overall snow pack. Rollerballs, point releases, and sloughs are all signs of rapid warming.

Unlike the other red flags that tend to appear simultaneously (new snow, winds, natural avalanches), rapid warming may be the only red flag observation you make before the avalanche danger increases significantly.

recent observations

Partly cloudy skies and a north wind yesterday offset the 10-12 degree increase in air temperatures. A few small wet point releases slides occurred at the base of rocky ribs in the Mammoth Basin at 10,000 ft. yesterday. June Mountain was 8 degrees cooler and there was no loose wet activity in the Negatives.

Stability tests in the recent new snow in the Mammoth Lakes Basin did not show weakness within the new snow. 

 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 20 deg. F.
Max. temperature in the last 24 hours: 39 deg. F.
Average wind direction during the last 24 hours: N
Average wind speed during the last 24 hours: 15-20 mph
Maximum wind gust in the last 24 hours: 30 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 50 inches
weather

High pressure building over the western US brings warm and dry conditions through Tuesday. Yesterday's daytime highs were 10 to 12 degrees warmer in the Mammoth Lakes Basin with daytime highs in the mid 40's while the top of June Mountain warmed only a few degrees to 31F. Today will be 5-8 degrees warmer but breezy north winds will limit daytime temperatures to the upper 40's at mid elevations and the upper 30's above 10,000 ft. Night time lows are on the rise also and by Tuesday, night time temperatures will be above freezing.

Monday and Tuesday will be dry and warm, followed by a cooling trend mid week as a cut off low forms and wanders around central and southern California.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Sunday Sunday Night Monday
Weather: sunny clear sunny
Temperatures: 50 deg. F. 29 deg. F. 57 deg. F.
Wind direction: N N S
Wind speed: 15-20 15-20 5
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Sunday Sunday Night Monday
Weather: sun clear sun
Temperatures: 36-42 deg. F. 28 deg. F. 54 deg. F.
Wind direction: N E S
Wind speed: 15-25 15-25 5
Expected snowfall: 0 in. 0 in. 0 in.
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