Eastern Sierra Avalanche Forecast - 3/21/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 22, 2014 @ 7:05 am
Avalanche Advisory published on March 21, 2014 @ 7:05 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is generally LOW for the Mammoth Basin and June Mountain areas. On high elevation north facing slopes in Rock Creek, a thick layer of large depth hoar continues to demonstrate weakness: though it is unlikely, a heavy load like a cornice drop could cause the depth hoar to collapse. Generally safe avalanche conditions exist; though watch for shallow weak snow below ridgetops and in steep gullies in north facing terrain.

Wet loose snow activity may increase today due to a poor refreeze and if high clouds persist during the day.  Small isolated areas of loose wet snow instability could occur today on sunbaked slopes in alpine areas and in the trees around rock outcrops and ribs. 

The avalanche rose is filled out for alpine and mid elevation terrain in the trees. Areas with grey shading either have no snow or there is no snowpack information available from these aspects and elevations. 

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 for the Mammoth Basin and June Mountain areas. On high elevation north facing slopes in Rock Creek, a thick layer of large depth hoar continues to demonstrate weakness: though it is unlikely, a heavy load like a cornice drop could cause the depth hoar to collapse. Generally safe avalanche conditions exist; though watch for shallow weak snow below ridgetops and in steep gullies in north facing terrain.

Wet loose snow activity may increase today due to a poor refreeze and if high clouds persist during the day.  Small isolated areas of loose wet snow instability could occur today on sunbaked slopes in alpine areas and in the trees around rock outcrops and ribs. 

The avalanche rose is filled out for alpine and mid elevation terrain in the trees. Areas with grey shading either have no snow or there is no snowpack information available from these aspects and elevations. 

  • Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Loose Wet
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Spring arrived yesterday though it has felt like spring for a month.  Energy from the sun has transformed the mid elevation snowpack in the trees in the Sherwins and glades in the Mammoth Lakes Basin to a spring snowpack in the upper layers. Snow temperatures in the upper 2 feet of the snowpack are close to freezing and a few ice masses can be found mid pack, showing that surface melt has traveled through the March snow and into some of the crust/facet combos that formed during and after the small impotent storms that characterized most of the winter storms. What this means for avalanche conditions is that small loose wet slides might occur but they will probably be small and isolated to sun exposed east and southeast facing slopes in the trees and possibly in alpine terrain.  A cool down tomorrow will further limit wet snow development.  

Avalanche Problem 2: Persistent Slab
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Steep, north facing slopes in alpine areas above tree line are getting a couple of hours of sun each day. Slopes steeper than 45 degrees are just now getting direct sun. Snow temperatures range from -3 to -5 in the Mammoth Lakes Basin. Rock Creek has much colder snow temperatures due to a generally colder climate than Mammoth. The combination of cooler temperatures, shaded north facing slopes and a shallow two to three foot snowpack has created continental snowpack conditions.

Several days ago, I reported ECT’s failing on a thick 5 mm depth hoar layer. Yesterday, Ned Bair reported ECTP21 for a one meter and two meter extended column test at 10,300 ft. on a slope similar to my tests. Compression tests yielded similar results with sudden collapse on the depth hoar layer. No signs of recent avalanches, whumpfing or cracking were observed.

The LOW avalanche danger rating means generally safe avalanche conditions. Small avalanches can occur in isolated areas but there are many downed trees and rocks above the snow surface which is why human triggered avalanches are unlikely.

recent observations

Several days ago, I reported ECT’s failing on a thick 5 mm depth hoar layer. Yesterday, Ned Bair reported ECTP21 for a one meter and two meter extended column test at 10,300 ft. on a slope similar to my tests. Compression tests yielded similar results with sudden collapse on the depth hoar layer. No signs of recent avalanches, whumpfing or cracking were observed. 

Snow temperatures in the upper meter of the snowpack near the Hose today showed snow temperatures close to freezing or 0C. A few ice masses were observed, showing that surface melt has traveled through the March snow and into some of the crust/facet combos that formed during and after the small impotent storms that characterized most of the winter storms.

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 26 deg. F.
Max. temperature in the last 24 hours: 50 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 20-30 mph
Maximum wind gust in the last 24 hours: 35 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 0 inches
weather

High clouds and seasonal daytime temperatures are forecasted for today before a weak cold front passes through and temperatures fall 8 to 10 degrees on Saturday. There is a very slight chance of showers tonight at ridgetop level. Daytime highs at 9,000 to 10,000 ft. will be in the mid to upper 40’s today, falling 8 to 10 degrees tomorrow.  Night will be cool with lows in the low to mid 20’s. West and southwest winds pick up this afternoon in the 15-20 mph range. Winds shift to the north on Saturday and high elevation temperatures will cool slightly to the upper 30’s with northeast to east winds.   

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: partly cloudy slight chance snow mostly sunny
Temperatures: 42 deg. F. 24 deg. F. 40 deg. F.
Wind direction: West West northeast
Wind speed: 5-15 5-15 5
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: partly sunny slight chance of snow mostly sunny
Temperatures: 47 deg. F. 21 deg. F. 39 deg. F.
Wind direction: West West north
Wind speed: 5-15 5-15 5
Expected snowfall: 0 in. 0 in. 0 in.
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