Eastern Sierra Avalanche Forecast - 4/10/14

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THIS AVALANCHE ADVISORY EXPIRED ON April 11, 2014 @ 1:49 pm
Avalanche Advisory published on April 10, 2014 @ 1:49 pm
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is MODERATE today on all north to east facing high elevation slopes. Continued warm temperatures, high clouds and sun will make wet avalanches possible in steep terrain on all east to north facing aspects.  In Rock Creek, wet slab avalanches are possible today on north to east facing slopes above 10,000 ft. 

It is spring out there and conditions are variable--wet avalanches, buried depth hoar and very isolated wind slabs. Expect snow conditions to change with changes in aspect, slope shape and elevation.  Start early, get off the snow by early afternoon. Avoid travel on and beneath steep snow covered slopes, especially avoiding confined gullies and terrain traps. Move to cooler, and/or shadier terrain if you see "pin wheels", smaller wet avalanche activity, or if the surface snow turns wet and sloppy. 

 

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 is MODERATE today on all north to east facing high elevation slopes. Continued warm temperatures, high clouds and sun will make wet avalanches possible in steep terrain on all east to north facing aspects.  In Rock Creek, wet slab avalanches are possible today on north to east facing slopes above 10,000 ft. 

It is spring out there and conditions are variable--wet avalanches, buried depth hoar and very isolated wind slabs. Expect snow conditions to change with changes in aspect, slope shape and elevation.  Start early, get off the snow by early afternoon. Avoid travel on and beneath steep snow covered slopes, especially avoiding confined gullies and terrain traps. Move to cooler, and/or shadier terrain if you see "pin wheels", smaller wet avalanche activity, or if the surface snow turns wet and sloppy. 

 

  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Wet
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    Same

The snowpack will take on alot of heating from the sun today- Wet snow avalanches are temperamental, especially  after several days after the initial rapid warmup and natural wet snow avalanche cycle on Sunday. Sometimes they turn off and sometimes they just keep coming. Even though daytime temperatures are slightly lower today, temperatures from remote station at 9,000 to 9,500 ft show temperatures above freezing for the last 48 hours or more.Traversing mid-path or in runout zones of steep, sunny avalanche paths should be avoided as things warm up today.

The Utah Avalanche Center posted statistics for fatal accidents that occur in dry and wet snow. 

The vast majority of people who die in wet snow avalanches die in natural avalanches, not human triggered slides. 

"Statistics for wet slides are approximate, but the take home point is that most people that die in wet snow avalanches die in natural avalanches, not human triggered slides". Thanks to Evelyn Lees of the Utah Center. 

Avalanche Problem 2: Wet Slab
  • Character ?
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  • Size ?
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    Increasing Danger

Rock Creek has a completely different snowpack structure than what is found in Mammoth or the June Mountain area. The pack is 2 to 3 ft deep at 10,000 ft on north facing slopes and deeper depths have been measured at the 11,000 ft elevation. Poor snowpack structure is responsible for continued sudden collapse failures on basal depth hoar. Wet slab avalanches are possible today. 

Night time lows have been in the mid 20's with warm days. On some slopes facing east and west, spring snow has formed. 

 

advisory discussion

Daytime highs yesterday hit 60F at the study plot at Mammoth Mountain after a morning low of 40 degrees.  The plots show the double whammy of increasing daytime and night time temperatures at Mammoth Pass and Gem Pass (10,700 ft).  Night time temperatures at Mammoth Pass have reached freezing three nights out of 4. The high elevation Gem Pass station reached freezing for a few hours the last three nights out of 4.  

Air temperatures by itself is not an effective indicator of wet snow avalanches. Wet snow avalanches occur as a result of energy entering the snow and the snowpack stratigraphy. Water is being produced by melt in the upper 30 cm or so in the higher elevations above 10,500 ft in the Mammoth Lakes Basin. 

The snow that fell at the very end of March is still fine grained and tends to hold water better compared to spring snow that has been through several melt freeze cycles. As warm days and mild nights continue, the end of March snow will reach the point where it can't hold any more water and another natural wet snow avalanche cycle may result or the snow into undergo enough melt freeze cycles and become a large grained snowpack that lets water pass through. 

recent observations

There are a variety of observations to report today.

Compression tests and extended column tests failed on depth hoar yesterday on north facing slope at above 10,000 ft yesterday.

Wet loose snow avalanche activity calmed down on Thursday in the Negatives and the Mammoth Basin with no recent wet snow activity observed. 

Skiing and riding conditions are generally good in alpine terrain but travel through mid elevation mush is tedious and slow.   

A temperature profile in a pit dug at 10,500 ft below the Mammoth Crest yesterday show the upper 12 to 14 inches of the snowpack was 32F (0C). This snow was deposited at the end of March. Below the new snow/old snow interface to 40 inches down ( 1 meter) snow temps ranged from -2 to -4C. The total snowpack depth was 7 ft (215 cm). 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 38 deg. F.
Max. temperature in the last 24 hours: 60 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 25 mph
Maximum wind gust in the last 24 hours: 36 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 38 inches
weather

Morning temperatures are balmy again this morning. Overnight lows are in the upper 30's. Daytime temperatures cool off a few degrees today after yesterday's summer like weather. Daytime highs yesterday hit 60F at the study plot at Mammoth Mountain and 64 at Mammoth Pass. Gem Pass at 10,700 ft reached  60 degrees. and the morning low is 32F.  

Isolated thunderstorms are possible this afternoon and Saturday. Storms that develop will produce lightening and brief periods of heavy rain, bursts of intense graupel and gusty winds.

Long range models show the potential for the storm track to return to the region mid/late next week but there is some uncertainty in terms of rain/snow potential.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Thursday Thursday Night Friday
Weather: clouds with chance of thunderstorms clouds, chance rain or snow slight chance of rain or snow
Temperatures: 54 deg. F. 53 deg. F. 49 deg. F.
Wind direction: W W N
Wind speed: 5-10 5-10 5-10
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: partly cloudy with thunderstorms partly cloudy with thunderstorms partly cloudy with thunderstorms
Temperatures: 53 deg. F. 31 deg. F. 52 deg. F.
Wind direction: W W NW
Wind speed: 5-10 5-10 10
Expected snowfall: 0 in. 0 in. 0 in.
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