Avalanche Advisory: Tuesday - Feb 13, 2018

THIS AVALANCHE ADVISORY EXPIRED ON February 14, 2018 @ 6:42 am
Avalanche Advisory published on February 13, 2018 @ 6:42 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

MODERATE avalanche danger exists today at tree-line and above in the form of fresh wind slabs as a result of strong NE winds and 2-6” of new snow.  These sensitive wind slabs are likely to be found just below ridge-lines and the side walls of gullies on NW-W-S-SE facing slopes.  Avoid steep slopes with deeper denser wind-deposited snow. 

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
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    Historic
    Very Large
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New light snowfall yesterday and last night resulted in 2-6” of new snow.  NE winds, while relatively light below tree-line, were stronger than expected at upper elevations yesterday resulting in considerable snow transport in some areas.  Today, NE winds are expected to be even stronger gusting into the 70mph range over ridge-tops before shifting out of the E and becoming light in the afternoon.  Fresh knee-high drifts were observed along the ridge-top of the negatives yesterday afternoon resulting from up-slope NE winds.  Fresh newly formed and still-forming wind slabs sensitive to human triggering are most likely to be found on NW-W-S-SE facing slopes at tree-line and above on the leeward side of ridgelines, the sidewalls of gullies, and around other features that promote drifting.  Be on the lookout for areas with deeper, denser snow deposits, and watch for signs such as shooting cracks from your skis indicating that new wind deposits are likely sensitive to human triggering.  Avoid slopes steeper than ~32 degrees where these conditions may exist. 

advisory discussion

Wind slabs are the most dangerous avalanche problem in the Eastern Sierra, and are responsible for most of the accidents and fatalities that occur here.  Subtle changes in topography within just a few feet can mean the difference between a totally stable safe spot and a spot that is teetering on the edge of failure.  With conditions like today, one could climb all day up a NE facing slope on completely stable snow, only to drop in the other side of the ridge on a steep SW facing slope and trigger a 2 foot deep wind slab.  Or it could even be as subtle as wrapping around to a NW facing slope and finding that pocket of unstable wind deposited snow.  While 2-6” of new snow is not a lot to be worried about on it’s own, a couple hours of wind can turn those inches into feet.  Wind slabs generally stabilize relatively quickly, usually within a day or 2.  But cold temperatures, slick icy melt-freeze crusts, or underlying loose faceted old surface snow, could all extend the time it takes for wind-slabs to bond.

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2/12: June - Negatives - Wind loading

2/12: Mammoth Crest - Blue Crag - New snow and light winds

Weather and CURRENT CONDITIONS
weather summary

As the tail-end of a weak low pressure system exits the Eastern Sierra this morning, a few scattered flurries could linger with no new accumulation.  Expect highs in the low 20s around 10,000’ and NE winds gusting up to 70mph over ridgetops in the morning before calming considerably in the afternoon and shifting out of the E.  

For Wednesday, expect sunny skies before another weak cold front results in increased winds, and possibly some scattered flurries in the evening, unfortunately with no accumulation expected.  Temperatures will rebound to above normal for the weekend, before dropping again with another cold front, possibly ushering in unsettled weather for next week. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy then becoming partly cloudy. Isolated snow showers in the morning. Partly cloudy then becoming clear. Sunny then becoming partly cloudy.
Temperatures: 26 to 32 deg. F. 10 to 16 deg. F. 31 to 37 deg. F.
Mid Slope Winds: Northeast Light Light winds becoming southwest in the afternoon
Expected snowfall: trace in. 0 in. 0 in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy then becoming partly cloudy. Isolated snow showers in the morning. Partly cloudy then becoming clear. Sunny then becoming partly cloudy.
Temperatures: 19 to 25 deg. F. 11 to 17 deg. F. 25 to 30 deg. F.
Ridge Top Winds: Northeast becoming East in the afternoon. Light winds becoming southwest after midnight. Southwest.
Expected snowfall: trace in. 0 in. 0 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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