Eastern Sierra Avalanche Forecast - 3/29/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 30, 2014 @ 10:39 pm
Avalanche Advisory published on March 29, 2014 @ 10:39 pm
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is CONSIDERABLE today on north facing high elevation slopes. Natural avalanches are possible on steep, wind drifted slopes and human triggered avalanches are likely on steep north to east facing slopes in exposed alpine terrain. You are most likely to trigger soft slab avalanches on fat, rounded pillows of snow on leeward slopes. In the past 6 hours, a rapid load has put stress on the snowpack and slopes that are wind loaded received even more stress. 

Out of wind affected terrain, the avalanche danger is MODERATE for triggering new snow sluffs and soft slabs on steep aspects on north to east facing slopes.

Careful snowpack evaluation, cautioous route finding and conservative decision making are essential today. 

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 CONSIDERABLE today on north facing high elevation slopes. Natural avalanches are possible on steep, wind drifted slopes and human triggered avalanches are likely on steep north to east facing slopes in exposed alpine terrain. You are most likely to trigger soft slab avalanches on fat, rounded pillows of snow on leeward slopes. In the past 6 hours, a rapid load has put stress on the snowpack and slopes that are wind loaded received even more stress. 

Out of wind affected terrain, the avalanche danger is MODERATE for triggering new snow sluffs and soft slabs on steep aspects on north to east facing slopes.

Careful snowpack evaluation, cautioous route finding and conservative decision making are essential today. 

  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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In alpine and exposed terrain, last night's and this morning's snowfall was easily transported by the wind to lee-ward terrain and pockets. Winds are strong enough this morning to continue moving snow on leeward slopes and the danger will remain elevated today. Expect to find fresh wind slabs and drifts on primarily  N-E aspects at upper elevations. You're most likely to trigger a wind slab on steep slopes where more than 10" of recently wind deposited snow exists.

Early morning observations of sensitive wind slabs and fat, wind loaded terrain in the Negatives indicate dangerous avalanche conditions. Wind slabs will be widespread on all leeward slopes above treeline. However, the winds are channeled by the terrain in the mountains, and can end up drifting snow onto a surprising variety of aspects and elevations. Identify the rounded, pillowy wind drifts  they are, and avoid them on all steep slopes.

I copied this graphic from the Utah avalanche center to illustrate where you can find wind slabs today. 

Avalanche Problem 2: Persistent Slab
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The shallow snowpack on north facing slopes above 10,000 ft in the Rock Creek area is weak and can be classified as a continental snowpack. On steep sheltered north facing slopes, depth hoar forms an thick, 6-8 inch layer. in wind exposed terrain above treeline, a variety of wind slabs and patchy areas of soft snow exist but the depth hoar layer is still there.  Additional loading occurred last night and Monday's storm will add more of a load. Avoid steep north facing terrain greater than 35 degrees in Rock Creek. Human triggered avalanches are possible today in steep north facing terrain. 

advisory discussion

The storm snow from the mid week storm appeared to have bonded well to the old snow surface since no natural or skier triggered slides were reported. Loose sluffs wre observed in the Rock Creek area on east facing slopes. Today, we have received enough new snow and wind-loading to create a wind slab hazard in alpine and exposed terrain in the trees. On steep sheltered terrain in the trees, human-triggered avalanches are possible where one foot or more storm snow has accumulated.

 

recent observations

On Friday, reports from the Mammoth Basin found generally stable conditions with excellent riding.

In Rock Creek, extended column tests and a 2 meter test failed in sudden collapse on 4-6 mm depth hoar.

     Be cautious when skiing or riding in the Rock Creek area above 10,000 ft.

 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 18 deg. F.
Max. temperature in the last 24 hours: 35 deg. F.
Average wind direction during the last 24 hours: WSW
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 inches
Total snow depth: 50 inches
weather

Skies are clearing this morning and 10 inches of new snow has fallen on June, Mammoth Mountain and in Rock Creek. West and southwester winds are blowing in the 20 mph range at the 9,000 ft elevation and in the 30-40 mph range along the ridgetops. Morning temperatures are in the teens and 20's. Expect partly cloudy skies today and gusty west winds along the ridgetops.  Another storm brings more snow to the area Monday night. Expect unsettled weather this week with possible snow throughout the week. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Saturday Saturday Night Sunday
Weather: snow showers cloudy clouds and snow
Temperatures: 30 deg. F. 26 deg. F. 22 deg. F.
Wind direction: West SW SW
Wind speed: 10-15 10 15-20
Expected snowfall: 1 in. 0 in. 1 in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: clouds and snow showers clouds partly cloudy
Temperatures: 24-30 deg. F. 12-18 deg. F. 24 deg. F.
Wind direction: West SW SW
Wind speed: 25-35 15-20 15-25
Expected snowfall: 2 in. 0 in. 1 in.
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