Eastern Sierra Avalanche Forecast - 2/28/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 1, 2014 @ 12:00 am
Avalanche Advisory published on February 28, 2014 @ 12:00 am
Issued by Sue Burak - Inyo National Forest
bottom line

Snow is beginning to fall this morning as a very strong storm moves into the area. This morning the avalanche danger is CONSIDERABLE in alpine zones above treeline and MODERATE at mid elevations. As storm snow accumulates later this morning, the avalanche danger could increase to HIGH over the Sierra Crest and possibly bump up to CONSIDERABLE at mid elevations. Human triggered avalanches are likely. Avoid backcountry travel above treeline. Large avalanches are possible.

 

How to read the advisory


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

Bottom Line

Snow is beginning to fall this morning as a very strong storm moves into the area. This morning the avalanche danger is CONSIDERABLE in alpine zones above treeline and MODERATE at mid elevations. As storm snow accumulates later this morning, the avalanche danger could increase to HIGH over the Sierra Crest and possibly bump up to CONSIDERABLE at mid elevations. Human triggered avalanches are likely. Avoid backcountry travel above treeline. Large avalanches are possible.

 

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

All steep terrain has the potential for avalanching today. The relentless winds of Thursday created layers of soft wind slabs and are now the old snow surface for a new round of wind slabs- precipitation rates will be higher and sustained for a longer time period than Thursday's storm. Slabs may be 3 to 5 feet thick. Yesterdays soft slabs felt more dense and cracks propagated farther than during the wet storm in early February.  The snowpack is in a very dynamic state today and will have to adjust to rapid loading later today.

Yesterday, natural avalanches occurred on in the Negatives and ski cuts and hand charges on June Mountain easily released soft slab avalanches that ran on the old snow surface from this week. Today, all wind loaded slopes are suspect at mid elevations- watch for obvious signs of loading such as cornices, rounded drifts and rippled texture of the snow surface.  Avoiding slopes where these signs are present will be a simple way to stay out of trouble in glades and tree skiing today. 

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

The most recent storm added about an inch of water in a couple of hours. It was enough water weight added in a short period of time to trigger a natural avalanche cycle in the Negatives.  More loading is happening now. Whether today's additional load will activate the deep buried depth hoar and facet layer is hard to know but being aware it is happening should inform travel routes today in the trees- avoid wind stripped slopes where the snowpack is thin or steep convex rollovers.

recent observations

The snowpack was actively adjusting to the new snow load yesterday in the Mammoth Lakes Basin. Gusty winds reached into sheltered glades. New snow was dense and formed soft slabs in exposed places in the trees. Cracks propagated while trail breaking. ECT tests done on north and east facing, low angle slopes cracked and propagated in the 1-10 tap range.  Propagation occurred between the old snow surface and storm snow. 

June Mountain ski patrol reported a widespread natural avalanche cycle in the Negatives.

 

 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 23 deg. F.
Max. temperature in the last 24 hours: 37 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 50 mph
Maximum wind gust in the last 24 hours: 80 mph
New snowfall in the last 24 hours: 10-18 inches
Total snow depth: 42 inches
weather

A WINTER STORM WARNING is in effect today until 10 PM tonight. The heavist period of snow will occur from 8AM to 2 PM today.  14-18 inches of snow is expected to fall in the town of Mammoth Lakes and over 2 feet is expected to accumulate above 8,000 ft. Winds will pick up this morning, gusting to 50 mph along highway 395 and 65 mph above 8,000 ft. Temperatures reach the mid 20's at the 8,000 ft elevation  and low 20's above 10,000 ft.

 

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Friday Friday Night Saturday
Weather: snow snow showers partly cloudy
Temperatures: 28 deg. F. 21 deg. F. 29 deg. F.
Wind direction: S SW S
Wind speed: 25-30 15-20 20-30
Expected snowfall: 10-16 in. 3-5 in. 0 in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: snow snow snow
Temperatures: 27 deg. F. 20 deg. F. 30 deg. F.
Wind direction: S SW S
Wind speed: 25-45 25-35 20-30
Expected snowfall: 10-14 in. 3-5 in. 1-3 in.
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