Eastern Sierra Avalanche Advisory - 3/24/17

THIS AVALANCHE ADVISORY EXPIRED ON March 25, 2017 @ 6:08 am
Avalanche Advisory published on March 24, 2017 @ 6:08 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

As SW winds increase and new snow accumulates this afternoon with 4-10” possible before nightfall, windslab avalanches will be of increasing concern throughout the day.  Natural avalanches will become possible and human trigger avalanches likely on steep slopes where winds deposit snow.  Sensitive windslabs will likely be found on the leeward side of ridges, side-walls of gullies and around other features that promote drifting.  Careful snow pack evaluation, cautious route-finding and conservative decision-making will be essential.   

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Avalanche Problem 1: Wind Slab
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Increasingly strong southwest winds combined with 6-10” of new snow that fell Tuesday and Wednesday, and an additional 4-10” of new snow expected to fall this afternoon will lead to sensitive wind slab formation on leeward slopes.  In general, northwest thru northeast thru southeast 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 terrain.  Be on the lookout for denser snow and use clues such as cornice formation and wind etching on the snow surface to identify areas of concern.  Yesterday (Thursday), winds were fairly light out of the north, giving older windslabs a chance to stabilize, but in rare areas these older windslabs may still be sensitive to human triggering. 

In areas where new snowfall amounts are on the greater end of the 4-10” spectrum, human triggered loose dry sloughs could occur in steep wind-sheltered terrain.  While these are likely to be small, they could be enough to knock a person off balance. 

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.  The avalanche concern shifted quickly from concerns over wet snow instability as slopes warmed from sunshine and warm air temperatures to cold snow sensitive wind slab formation.  Yesterday’s sunshine however brought back the wet snow concern on solar aspects, as rollerballs and wet-slide debris was reported by parties in the convict area and twin-lakes bridgeport area yesterday.  More storms today thru the beginning of next week will keep folks on their toes, as concerns will shift back toward wind slabs, with the added concern of wet snow instabilities on solar aspects as sunshine comes back out in between storms.    

recent observations
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-3/23 - Convict Area - Small wind slab avalanches and wet slides

-3/23 - Twin Lakes / Bridgeport Area - Wind slab and wet slides

-3/23 - Rock Creek Area - Wet and heavy snow, variable conditions

-3/23 - Mammoth Mountain - Patrol results: many small wind slab releases from explosives

-3/22 - June Area - Weather and snow surfaces

-3/22 - Chicken Wing (near June) - Small wind slabs

-3/22 - Sherwins (Mammoth) - Small isolated windslabs, conditions

Weather and CURRENT CONDITIONS
weather summary

An active weather pattern will continue through early next week as a couple of cold fronts move in bringing more snow and wind.

Friday:  Clouds will increase this morning until snow begins by afternoon with 4-8” of accumulation before nightfall.  Strong SW winds will be on the increase as well with gusts expected over 80mph over 10,000’ by afternoon.  Expect high temperatures to reach the upper 30s around 10,000’ before cooling this afternoon.  Tonight snow will continue with 4-10” of additional accumulation with continued SW winds.

Saturday:  Expect snowfall and winds to diminish by morning, with little additional accumulation and west winds gusting up to 40mph above 10,000’.  Highs will be in the upper 20s around 10,000’. 

Long-term:   Another storm will bring more snow beginning Sunday night through Monday.  Mix of sunshine and possible snow showers through the middle of the week.

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: Mostly cloudy then becoming cloudy. Chance of snow and rain Cloudy. Snow in the evening, then chance of snow after midnight. Mostly cloudy. Slight chance of snow showers through the day.
Temperatures: 38 to 48 deg. F. 22 to 28 deg. F. 31 to 39 deg. F.
Mid Slope Winds: S SW Light
Expected snowfall: Up to 6 in. 5-10 in. up to 1 in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy then becoming cloudy. Chance of snow in the morning, then snow in the afternoon. Cloudy. Snow in the evening, then snow likely after midnight. Mostly cloudy. Chance of snow showers in the morning, then slight chance of snow showers in the afternoon.
Temperatures: 31 to 41 deg. F. 16 to 22 deg. F. 22 to 30 deg. F.
Ridge Top Winds: SW SW W
Expected snowfall: up to 5 in. 4 to 9 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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