Avalanche Advisory: Saturday - Jan 27, 2018

THIS AVALANCHE ADVISORY EXPIRED ON January 28, 2018 @ 7:00 am
Avalanche Advisory published on January 27, 2018 @ 7:00 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

With almost 2 days now since the development of any new wind slabs, the avalanche danger has decreased to LOW.  This means that human triggering is overall unlikely, but not impossible.  Isolated areas of wind slab sensitive to human triggering are most likely to be found lingering in steep (>35deg) NW-N-NE facing terrain especially at upper elevations just below ridges or the sidewalls of gullies.    

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Wind Slab
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Isolated areas of sensitive wind slab may still be found lingering in steep (>35deg) NW-N-NE facing terrain.  Although unlikley, it is not impossible that a human could trigger one of these lingering wind slabs.  Strong SW to W winds accompanied 3-10” of new snowfall on Thursday, which led to sensitive wind slab development in exposed areas.  On Wednesday, VERY strong SW-W winds blew enough to transport the old loose snow into some very dense wind slabs, which observations over the past couple of days have found to be actually more sensitive and concerning than the overlying less dense newer snow deposits.  It has now been almost two days with light winds, and no noteable wind transport of snow.  Wind slabs become harder to trigger and strengthen with time, but just how long that takes could be from a few hours to a few days.  Look and feel for smooth firm snow, hollow sounds, and realize that very dense wind slabs from Wednesday could be covered by less dense snow on the surface.  Do your own localized assessments of how well isolated wind slabs are bonding, and recognize that great variability exists even across small areas on a slope.  Loose sugary facets directly under a wind slab could extend its period of sensitivity.  Wind slabs are likely to be found in leeward areas just below ridgelines, the sidewalls of gullies, cross-loaded slopes and around other features that promote drifting. 

Avalanche Problem 2: Persistent Slab
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The shallow snowpack throughout much of our area has resulted in the formation of loose sugary layers of faceted snow deeper down in the snow.  Snow-pit tests have continued to show throughout most of the winter that areas exist where these layers have the potential to fail cleanly, and even more so lately with the past week of cold weather.  However the small storms we have had this year have not been significant enough to overload these weak layers and result in any reported avalanche activity, neither naturally nor human triggered.  That doesn’t mean that human triggering is impossible, just very unlikely.  Recognize that these layers exist, and that if an avalanche were triggered, it could be quite large.  Areas where these layers have been found to be most concerning are non-southerly facing slopes at tree-line and below.  Recognize that woomphing in low angle terrain could be an indication that a deeper weak layer has failed.  Like always, continue to use safe travel protocols on steep slopes, such as exposing one person at a time.     

advisory discussion

As the weather changes after this last cold storm, and temperatures begin to rise today, and continue to rise even more on Sunday and thru next week, with fully sunny skies, it is likely that we will soon be entering a period of loose-wet avalanche activity for sun-exposed slopes.  Be aware of this shift in attention as you begin to make plans for upcoming days, and stay tuned for further discussion. 

recent observations
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Snowpack and Weather observations:

-1/26: Mammoth - Sherwins - search for wind slabs1/25: June - Hemlock Ridge behind - New snow, patches of wind slab

1/25: Mammoth - TJ and Hammil Bowls - testing wind slabs and persistent deep layers

1/25: Mammoth - Redcone - storm snow

Evidence of Natural Avalanches on Thursday (1/25):

        -VA Lakes

        -Mammoth Crest

        -Negatives behind June

Weather and CURRENT CONDITIONS
weather summary

Expect partly cloudy skies today, light northwesterly winds, and above average temperatures with highs reaching the upper 30s around 10,000’.

The snow from this past Thursday’s storm looks to be the last we will see for awhile.  The long-term forecast is not looking good.  “The upper level ridge is expected to sharply amplify by Sunday heralding an extended period of warm, dry conditions.”  Expect dry conditions and well above normal temperatures with highs into the mid to upper 40s at 10,000’ thru all of next week and possibly thru mid-February as a blocking high pressure ridge sets in along the west coast.  The term “June-uary” from past years comes to mind … let’s hope that we don’t have to think of a new one for the month of February ….

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: Partly cloudy. Partly cloudy. Partly cloudy then becoming sunny.
Temperatures: 39 to 47 deg. F. 21 to 29 deg. F. 47 to 53 deg. F.
Mid Slope Winds: West Light Light
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Partly cloudy. Partly cloudy. Partly cloudy then becoming sunny.
Temperatures: 33 to 38 deg. F. 22 to 27 deg. F. 39 to 44 deg. F.
Ridge Top Winds: Northwest Northeast Northeast
Expected snowfall: 0 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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