Eastern Sierra Avalanche Forecast - 2/1/14

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THIS AVALANCHE ADVISORY EXPIRED ON February 2, 2014 @ 7:11 am
Avalanche Advisory published on February 1, 2014 @ 7:11 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger rating is MODERATE. Human triggered avalanches are possible on steep mid and upper elevation north facing terrain in the Mammoth Lakes Basin.

 

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 rating is MODERATE. Human triggered avalanches are possible on steep mid and upper elevation north facing terrain in the Mammoth Lakes Basin.

 

  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Trend ?
    Same

The primary avalanche concern has changed from wind slabs to the unpredictable buried old weak snow that was the snowpack for December and January.  The persistent weak layer is the facets and depth hoar that were the snowpack in December and January. This layer can continue to produce skier triggered avalanches for days, making them especially dangerous.

 

While there was not enough of a new snow load to cause a natural avalanche cycle, extended column test results show that buried depth hoar is still capable of producing avalanches. The problem is that depth hoar and large facets on the ground are not found on all north facing slopes but on some slopes in the trees, at treeline and above treeline. This is a condition we call “pockety”- found on some but not all slopes at mid to high elevations. It’s up to you to figure out whether the slope you plan to ski harbors weak snow at the base of the snowpack.  

advisory discussion

Several of us skied to the Red Cone area yesterday and there was little indication of wind loading along the ridgetops. There was one very small lip along a ridge otherwise cornices were absent. Even though winds on Mammoth Mountain were sustained at 40-60 mph, there was very few signs of wind loading and wind drifted snow.  In comparison, avalanche control work on Mammoth Mountain produced good results with slab avalanches 10-16" deep were running 200 to 800 feet. The difference is remarkable.   

Three parties dug snowpits yesterday in the trees and right at treeline. Three pits, multiple extended column tests and differences in the thickness and size of the faceted layer at the base of the snowpack. One extended column test failed on depth hoar at the bottom of the pack, others did not crack or propagate.  The only generalization that can be made from the variety of snow structure and test results today is that there is a buried weak, faceted layer at the bottom of the snowpack. The ability of this persistent layer to cause a human triggered avalanche varies from slope to slope and at all elevations in the trees, at treeline and in the alpine zones. 

The extremely dry and mild weather this winter created a highly variable snowpack: the dry spells created sun crusts on north aspects as well as weak faceted snow sandwiched between the crusts. In some shaded areas, sun crusts did not form but in others, there are 4 sun crusts. This storm had added much needed substance to the snowpack but snow structure changes from slope to slope, aspect to aspect and from glades to scattered timber in the subalpine and in the alpine zones.  Obstacles still remain only they are better hidden with the new snow. 

 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 5 deg. F.
Max. temperature in the last 24 hours: 17 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: 1 inches
Total snow depth: 24 inches
weather

Winter temperatures have returned. Cold days and colder nights will continue for the week. Northerly flow will limits daytime highs to the mid to upper 20's after cold night time temperatures of single digits. Sunny days and cold northeast winds today gusting to 30 mph are forecasted for today. 

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: sun clear sun
Temperatures: 21 deg. F. 13 deg. F. 24 deg. F.
Wind direction: NE NE SW
Wind speed: 10 5-10 5
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: Sun partly cloudy slight chance snow
Temperatures: 21 deg. F. -7 deg. F. 19 deg. F.
Wind direction: NE SE SW
Wind speed: 5-10 5-10 10-15
Expected snowfall: 0 in. 0 in. 0 in.
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