Eastern Sierra Avalanche Advisory - 3/25/17

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THIS AVALANCHE ADVISORY EXPIRED ON March 26, 2017 @ 6:38 am
Avalanche Advisory published on March 25, 2017 @ 6:38 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center
bottom line

With up to a foot+ of new snow in some areas since yesterday and moderate SW winds, small to large wind slabs will be the greatest avalanche concern for today, followed by loose wet snow in the afternoon as skies clear and temperatures rise.  Natural avalanches will be possible, and human triggered avalanches likely.  Careful snow pack evaluation, cautious route-finding and conservative decision-making will be essential.   

How to read the advisory

Bottom Line

With up to a foot+ of new snow in some areas since yesterday and moderate SW winds, small to large wind slabs will be the greatest avalanche concern for today, followed by loose wet snow in the afternoon as skies clear and temperatures rise.  Natural avalanches will be possible, and human triggered avalanches likely.  Careful snow pack evaluation, cautious route-finding and conservative decision-making will be essential.   

Avalanche Problem 1: Wind Slab
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Moderate SW winds with up to a foot+ of new snow since yesterday will have led to sensitive windslab formation on the leeward side of ridges, side-walls of gullies and around other features that promote drifting.  In general, NW thru NE thru SE facing slopes will be of greatest concern, but be aware that swirling winds could lead to wind slab formation on any aspect in more complex mid elevation terrain.  Be on the lookout for denser snow and use clues such as cornice formation, wind etching on the snow surface, and shooting cracks from your skies to identify areas of concern.  Warm weather will likely lead to these windslabs stabilizing fairly quickly, but just how long is unknown.  Avoid steep wind-loaded slopes for now, and then do your own stability tests in coming days in safe representative areas before commiting to steeper more consequential terrain.  

Avalanche Problem 2: Loose Wet
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As skies clear and temperatures rise this afternoon, new snow will warm rapidly and loose wet slides will become likely.  Solar aspects facing E to S to W will be of greatest concern, but if some clouds remain N facing slopes will heat up and become unstable as well.  Loose wet slides will most likely start near rock bands which heat up faster and warm the sourounding snow.  This was seen on Thursday on some northerly facing slopes on Mt Wood which had evidence of recent small wet slides in the afternoon.       

Avalanche Problem 3: Loose Dry
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In areas sheltered from the wind that received greater amounts of new snow (in the foot+ range), loose dry sloughs will likely result from skier and rider turns in steep terrain.  While these are likely to be small, they could knock a person off balance, and could result in a burial if a terrain trap like a gully is involved or from snow accumulating on the uphill side of a tree.    

advisory discussion

Over 2 weeks of warm springtime weather came to an end early this week with the first in a series of cold fronts which dropped 6-12” of new snow with strong SW winds Tuesday and Wednesday, and then another storm which dropped up to another foot yesterday afternoon thru last night with moderate SW winds.  These new storms have shifted the avalanche concern from solely concerns over wet snow instability as slopes warmed from sunshine and warm air temperatures to now include sensitive wind slabs as well.  New cold snow will be especially susceptible to rapid warming, and rollerballs and small to medium wet slides will be likely as slopes warm.

 

weather

Unsettled weather will continue this weekend thru early next week bringing in weak storms with periods of light snow showers resulting in an inch or two of accumulation here and there.

Saturday:  Scattered light snow showers are likely in the morning with little new accumulation, then cloudy to partly sunny skies in the afternoon with warming temperatures reaching the mid 30s around 10,000’.  West winds will be fairly light with gusts up to 40mph above 10,000’ in the morning, diminishing in the afternoon. 

Sunday:  Expect mostly cloudy skies with light snow in the afternoon, with up to an inch of accumulation.  SW winds will increase slightly in the afternoon with gusts back into the 45mph range.  Temperatures should be fairly warm reaching the upper 30s at 10,000’.

Long-term:  A weak storm will continue to bring some snow showers Sunday night through Monday.  Winds should be on the increase as this disturbance exits the area, followed by dry weather thru the middle of next 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: Mostly cloudy. Scattered snow showers in the morning, then slight chance of snow showers in the afternoon. Partly cloudy. Mostly cloudy. Chance of snow in the afternoon.
Temperatures: 36 to 44 deg. F. 20 to 28 deg. F. 40 to 46 deg. F.
Wind direction: Light Light SW
Wind speed: Gusts up to 25 mph in the morning. Light 10 to 15 mph with gusts to 35 mph in the afternoon.
Expected snowfall: 0 in. 0 in. up to 1 in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: Mostly cloudy. Scattered snow showers in the morning, then slight chance of snow showers in the afternoon. Partly cloudy. Mostly cloudy. Chance of snow in the afternoon.
Temperatures: 28 to 36 deg. F. 17 to 23 deg. F. 34 to 40 deg. F.
Wind direction: W NW SW
Wind speed: 15 to 20 mph. Gusts up to 40 mph decreasing to 25 mph in the afternoon. 10 to 15 mph with gusts to 25 mph in the evening becoming light. 10 to 15 mph with gusts to 35 mph increasing to 20 to 30 mph with gusts to 45 mph in the afternoon.
Expected snowfall: 0 in. 0 in. up to 1 in.
Disclaimer
This Avalanche Advisory is designed to generally describe avalanche conditions where local variations always occur. This product only applies to backcountry areas located outside established ski area boundaries. The information in this Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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