Eastern Sierra Avalanche Forecast - 2/23/14

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THIS AVALANCHE ADVISORY EXPIRED ON February 24, 2014 @ 7:08 am
Avalanche Advisory published on February 23, 2014 @ 7:08 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is generally LOW; human triggered avalanches are unlikely on most slopes. Watch out for isolated areas above treeline where the snowpack is shallow.  Unstable slopes are very isolated and human triggered avalanche are unlikely - but not impossible. Identify and avoid thin areas on slopes where rocks or trees project above the snow surface. On east aspects, daytime solar heating may create surface wet snow instabilities

How to read the advisory


  • Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Bottom Line

The avalanche danger is generally LOW; human triggered avalanches are unlikely on most slopes. Watch out for isolated areas above treeline where the snowpack is shallow.  Unstable slopes are very isolated and human triggered avalanche are unlikely - but not impossible. Identify and avoid thin areas on slopes where rocks or trees project above the snow surface. On east aspects, daytime solar heating may create surface wet snow instabilities

  • Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Trend ?
    Decreasing Danger

The persistent layer is persistent. Depth hoar is rounding and the layer is strengthening but not at the same rate everywhere. This creates more variability on each slope than earlier in the winter when widespread areas of fist hardness depth hoar and facets made slope scale stability assessment alot easier. Avoid shallow, wind scoured areas and places where rocks are projecting above the snow surface. 

Avalanche Problem 2: Loose Wet
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Trend ?
    Increasing Danger

Night time temperatures are above freezing. Each night above freezing results in earlier warming of the snow surface during the day. Wet snow instabilities may become widespread on east facing mid elevation slopes below treeline.  East facing slopes above treeline may also develop localized aras of wet snow rock outcrops and cliffbands.

advisory discussion

The avalanche danger is generally LOW but there are places in steep alpine terrain where to watch out for. On wind loaded slopes where the snowpack is deep (4-5 ft.), buried facet layers are anywhere from 6 to 30 inches thick. A light trigger such as a skier is unlikely to impact the weak layer on slopes where the snowpack is deep and evenly distributed but this is not the case in the alpine zones of the Mammoth Lakes basin. Avoid areas on slopes if rocks or trees are shallowly buried or projecting through the snow surface.

Daytime and night time temperatures are warming. The sun is higher in the sky and the energy reaching a three sq. ft. section of snow is about the same amount of energy a solar panel produces. The snow surface is wet by mid-day at the 8500 to around 9800 ft. elevations. Melt freeze crusts are generally supportable and wet snow is found in the trees and east facing slopes. Night time temperatures may not dip below freezing over the next few days and wet snow instability is expected to increase.

recent observations

TJ Bowl area; ECTN30 on basal facets.  I found variable snow depths above Crystal Lake ranging from 24 to 50 inches with facet layers from 8" to 30 inches.  Some surface instabiity reported as near surface crusts failed in compression tests on small facets under the recent crust.

Near surface faceting is widespread above treeline due to localized temperature gradients caused by fluctuations of air temperature and solar radiation.

Observations over the last two days show rounding facets and depth hoar in response to the decreasing temperatrue gradient. Coarse depth hoar and facets may appear moist as they round  because of the smooth glassy appearance of the grains, however, the grains are not "moist" unless teh temperature of the snow is 0 C and the snow has a distinct tendency to stick together.  Photographs are taken from the International Classification for Seasonal Snow on the Ground.

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 21 deg. F.
Max. temperature in the last 24 hours: 32 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 15 mph
Maximum wind gust in the last 24 hours: 35 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 39 inches
weather

High pressure builds over the West the next few days. Daytime and night time temperatures are warming. Winds will be light even over the ridgetops. Daytime highs at the 8,000 to 10,000 ft elevations will be in the mid 50's. Lows could be in the mid 30's. Higher terrain will see mild daytime highs in the low 40's and nights will reach the low to mid 20's.

All eyes are watching every 12 hour update from the National Weather Service. There is increasing confidence in snowfall at the middle and end of next week.

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: clear, warm cler Sun
Temperatures: 50 deg. F. 27-32 deg. F. 52 deg. F.
Wind direction: SW SW SW
Wind speed: 5-10 5 5
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Sunday Sunday Night Monday
Weather: sun clear sun
Temperatures: 49 deg. F. 50 deg. F. 52 deg. F.
Wind direction: SW SW Sw
Wind speed: 5-10 5-10 5
Expected snowfall: 0 in. 0 in. 0 in.
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