Eastern Sierra Avalanche Advisory - 1/16/18

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THIS AVALANCHE ADVISORY EXPIRED ON January 17, 2018 @ 7:00 am
Avalanche Advisory published on January 16, 2018 @ 7:00 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

MODERATE avalanche danger persists on E-N-W facing slopes due to a weak snowpack structure of loose sugary faceted snow under firm dense snow.  Light snowfall with minimal accumulation is forecasted for today.  Small new sensitive wind slabs could form in leeward areas where snowfall far exceeds expectations due to moderate SW winds.

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: Persistent Slab
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The thin snowpack that exists throughout our forecast area has kept layers of loose sugary faceted snow under layers of firm dense snow alive and concerning.  While human trigger points remain very isolated, once triggered an avalanche of this type has the potential to be large and destructive.  Consider this potential, and do your own localized investigation thru digging before deciding to commit to steep consequential terrain. 

Avalanche Problem 2: Wind Slab
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Today’s snow forecast if 60% chance of up to 1”, 40% chance of 2-4”.  If areas exist that receive this greater amount, moderate SW winds will likely form pockets of new small wind slabs sensitive to human triggering at upper elevations.  Look out for new deposits of smooth dense snow on the leeward sides for ridges, on the sidewalls of cross-loaded gullies, and around other features that promote drifting.  While a resulting avalanche would likely be small, it could be enough to knock a rider off their feet into a nasty fall in consequential terrain. 

advisory discussion

Recent observations throughout the accessible snowy terrain continue to find many areas where layers of loose sugary faceted snow exist under more dense snow.  Tests continue to result in failures in these loose layers, some of which continue to show the potential for fracture propagation.  These are most concerning where these layers are shown to exist and be reactive 20-70cm down in the snowpack.  Reports of whoomphing on low-angle terrain continue to come in, which is an indication that weak layers deeper in the snowpack are failing.  While no avalanche activity has been reported involving these deeper persistent layers, the possibility exists, and if triggered, a resulting avalanche is likely to be large and destructive.    We hope that in-coming storms beginning toward the end of this week will be large enough to either result in widespread natural avalanche activity, effectively cleaning out these persistent layers of concern, or else bridging them over with enough snow where human triggering becomes much less of a threat.  

Weather and CURRENT CONDITIONS
weather summary

A weak storm will push through our area today, with moderate SW winds, and light snowfall resulting in little accumulation.  Temperatures will be quite a bit cooler than past days, with highs expected in the mid to upper 30s at 10,000’.

Wednesday is the calm before the “real” storm beginning Thursday morning and lasting thru Friday.  This storm, possibly the first moderate A.R. (Atmospheric River) of the season, will begin with a strong cold front dropping south into the Sierra with strong winds, followed by moderate to heavy mountain snow, with snow levels dropping significantly Friday morning.  While centered further to the north toward Tahoe, 1-2’ of snow in the mountains is still looking likely for our area.  Another weak to moderate A.R. is looking likely for early 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. Isolated snow showers in the morning. Partly cloudy. Mostly cloudy.
Temperatures: 41 to 47 deg. F. 28 to 33 deg. F. 46 to 52 deg. F.
Wind Direction: SW SW SW
Wind Speed: 10 to 15 mph. Gusts up to 45 mph decreasing to 30 mph in the afternoon. Light winds. Gusts up to 35 mph after midnight. Light winds becoming southwest 10 to 15 mph in the afternoon. Gusts up to 30 mph.
Expected snowfall: up to 1 in. 0 in. 0 in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy. Scattered snow showers in the morning. Partly cloudy. Mostly cloudy.
Temperatures: 34 to 39 deg. F. 24 to 29 deg. F. 40 to 45 deg. F.
Wind Direction: SW SW SW
Wind Speed: 25 to 40 mph with gusts to 60 mph decreasing to 15 to 25 mph with gusts to 40 mph in the afternoon. 15 to 25 mph. Gusts up to 30 mph increasing to 40 mph after midnight. 15 to 20 mph with gusts to 35 mph.
Expected snowfall: up to 1 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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