Eastern Sierra Avalanche Forecast - 3/2/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 3, 2014 @ 7:10 am
Avalanche Advisory published on March 2, 2014 @ 7:10 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is rated CONSIDERABLE in terrain steeper than 35 degrees above treeline. Slab avalanches will likely fail on mid storm weakness or step down to deeper layers and create a larger avalanche.  Avoid wind-loaded slopes, steep consequential terrain, and large avalanche path runouts. Cautious route-finding and conservative choices remain important today.

There are areas of CONSIDERABLE avalanche danger today in steep terrain at mid elevations. Watch out for steep convex terrain in the trees and avoid wind loaded slopes below corniced ridgelines.  Pick conservative lines and ski one at a time. 

 

How to read the advisory


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

Bottom Line

The avalanche danger is rated CONSIDERABLE in terrain steeper than 35 degrees above treeline. Slab avalanches will likely fail on mid storm weakness or step down to deeper layers and create a larger avalanche.  Avoid wind-loaded slopes, steep consequential terrain, and large avalanche path runouts. Cautious route-finding and conservative choices remain important today.

There are areas of CONSIDERABLE avalanche danger today in steep terrain at mid elevations. Watch out for steep convex terrain in the trees and avoid wind loaded slopes below corniced ridgelines.  Pick conservative lines and ski one at a time. 

 

  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Decreasing Danger

The snowpack has had some time to adjust to the new load and the avalanche danger is slowly decreasing following three days of intense wind loading. Most slopes have dangerous slabs just waiting for a trigger like a person. Watch for signs of avalanche activity that occurred during the storm and avoid slopes with similar aspects and slope angles. Be careful of the improving weather and look for human factor "red flags" within your group- like a person who is too excited about the new snow or a "ski to die" attitude.  

 

Avalanche Problem 2: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Same

The depth hoar layer is buried in many places under 3-5 feet of snow and more in wind loaded areas. While there is alot of snow resting over weak snow, don't forget the depth hoar layer in the Mammoth Lakes Basin is one to two feet thick and is closer to the surface in thin areas on slopes. You are most likely to start one of these large destructive avalanches along slope margins, where the deeper slab tapers and becomes thin. Avoid convexities or areas with a thin or variable snowpack. Put the odds in your favour by avoiding steep, unsupported slopes, areas with a thin or variable snowpack, or terrain with a significant overhead hazard

In these (and most) conditions, tracks do NOT equal stability. Cautious route-finding and conservative choices remain important today.

 

 

advisory discussion

Storm totals from Thursday Feb 27 through March 1 are impressive. 

Mammoth Pass: 33" snow, 3.7 inches water content

MMSP: 25" snow, 3.2" water content. Rock Creek: 23", 3.6" water. 

June Mtn study plot: 33" with 3.8 inches of water. 

Three to four inches of water is a heavy load- the most intense loading occurred Friday afternoon. 3-4 inches on the study plot does not come close to the amount of snow and wind loading that actually occurred above 10,000 ft.. Several days of sustained winds created multiple layers of wind slabs. The wind can transport snow to depths up to 10 times the amount recorded at study plots so it safer to be conservative and proceed cautiously in avalanche terrain today. The snow needs more time to adjust to the new load but there are always volunteer slope stability testers pushing the snowpack to stabilize faster. Remember that tracks on a slope do not mean the slope is stable. 

 

recent observations

Explosives work on MMSA released numerous slab avalanches mostly 2-3 ft deep within the storm snow. There was an explosives triggered avalanche on the Dragon's Tail that stepped down to the November facets. 

There was no recent ava activity observed in the Punta Bardini area. No propagation in ECT tests but consistent results (ECTN) noted within the storm snow about 15-16 inches down. A column test did result in Q1.5 failure with moderate force (13 taps) on rounding depth hoar at the bottom of the pack. 

ECT's  at 9,500 ft to 9,800 ft  in the Lks basin propagated easy to moderate range 12-14 inches down on graupel. Graupel and heavily rimed grains are found throughout the storm 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: 31 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 35-40 mph
Maximum wind gust in the last 24 hours: 99 mph
New snowfall in the last 24 hours: 2-3 inches
Total snow depth: 67 inches
weather

Skies will slowly clear today with winds veering to the NW as low pressure moves to the east. Scattered snow showers may persist at the higher elevations. Temperatures warm up a few degrees today. By Wednesday, daytime highs will be in the 40's. 

Winds taper off today with breezy west and northwest winds from 15-25 mph. The next chance of snow is mid week, but prospects do not look good for precipitation in our area. 

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: partly cloudy cloudy partly sunny
Temperatures: 35-41 deg. F. 20-23 deg. F. 36-40 deg. F.
Wind direction: South southwest northwest
Wind speed: 15-25 10-15 15-20
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Sunday Sunday Night Monday
Weather: clouds cloudy partly sunny
Temperatures: 25-30 deg. F. 18-20 deg. F. 26-32 deg. F.
Wind direction: SW SW NW
Wind speed: 15-25 15-20 15-25
Expected snowfall: 2-3 in. 0 in. 0 in.
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