Eastern Sierra Avalanche Advisory - 1/12/18

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON January 13, 2018 @ 6:24 am
Avalanche Advisory published on January 12, 2018 @ 6:24 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

Human triggered avalanches will remain possible today thanks to several persistent weak layers buried in our snowpack. Colder, northerly slopes near and above treeline remain the areas of greatest concern. Below ~9,000’ coverage is still thin and avalanches are unlikely.

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Recent wind deposits, though stubborn to trigger by themselves, have added a little more weight to the buried weak layers in our snowpack. Stability tests from the northern half of the forecast area continue to show that unconsolidated, sugary snow under denser slabs still have the potential for failure and if triggered, could propagate that failure across the slope. Whumphing noises and collapsing under your feet are signs of instability that you should not ignore. You will be most likely to trigger these buried hazards near, and just above treeline on colder northerly aspects and especially where previously wind-drifted snow has added a new load to the snowpack.

advisory discussion

Wind slabs left throughout the eastern Sierra from Wednesday’s wind event were stubborn, though not impossible to trigger. One skier caused a small avalanche yesterday morning on a convex slope near Crystal Lake on the Mammoth Crest. Light showers midday yesterday dusted the forecast area at middle and upper elevations. Strong Southwest winds may have transported some of that snow onto high North-easterly facing slopes creating very small and dense wind crusts. The warm temperatures and relatively high humidity have promoted settlement in the recent storm snow. All of this together will add a little more weight, and slightly denser slabs on top of the persistent weak layers buried on cooler northerly slopes. These layers of poorly bonded, sugary facet snow still exist near crusts and denser layers and can be found around 30-45cm and 65cm down in the snowpack. In some areas, where the overall snow depth is thinner, large facet crystals can still be found near the ground. Tests yesterday showed that the potential for failure in these layers has not gone away. Whumphs under your feet are a sign of collapse in one of these weak layers. Digging down and doing some extra detective work can tell you if these layers are likely to fail on the slopes you want to ride.

Warm temperatures today will likely cause some moist snow, roller ball activity, and melting below ~9,000’ and on sunny aspects.

Weather and CURRENT CONDITIONS
weather summary

Dry conditions and above average temperatures are expected today and through the weekend as high pressure builds into northeast California and western Nevada. More active weather is expected next week, especially by late week, as the stronger of two systems moves through the region.

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: Sunny. Clear. Partly cloudy then becoming sunny.
Temperatures: 44 to 50 deg. F. 23 to 33 deg. F. 47 to 53 deg. F.
Wind Direction: SW Light winds. Light winds.
Wind Speed: 10 to 15 mph with gusts to 50 mph in the morning becoming light. Light winds. Gusts up to 25 mph after midnight. Light winds. Gusts up to 35 mph in the morning.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Sunny. Clear. Partly cloudy then becoming sunny.
Temperatures: 38 to 43 deg. F. 27 to 32 deg. F. 41 to 46 deg. F.
Wind Direction: W NE SE
Wind Speed: 30 to 45 mph with gusts to 70 mph decreasing to 20 to 30 mph with gusts to 45 mph in the afternoon. 15 to 20 mph with gusts to 30 mph. 15 to 25 mph with gusts to 35 mph in the morning becoming light.
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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