Avalanche Advisory: Friday - Dec 20, 2019

THIS AVALANCHE ADVISORY EXPIRED ON December 21, 2019 @ 6:44 am
Avalanche Advisory published on December 20, 2019 @ 6:44 am
Issued by Steve Mace - ESAC

The avalanche danger is LOW today at all elevations. Isolated areas of unstable snow exist on northerly aspects near and above treeline where pockets of dense stubborn wind slab are sitting on weakening loose snow. Small avalanches are still possible on isolated terrain features or in extreme terrain.

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

It will still be possible to find isolated areas where lingering wind slabs are sensitive to human trigger. Recent observations have found poor snowpack structure in multiple areas throughout the range where thick, dense wind slabs are sitting on weak faceted snow below.  These areas are likely isolated to specific terrain features on more northerly aspects at mid and upper elevations where a relatively thin snowpack exists. The leeward side of ridgelines and the sidewalls of gullies are of particular concern.  Use surface clues to identify wind loaded areas and do your own localized assessments to see if this poor structure exists before committing to a suspect slope.  While hard to trigger, a resulting hard slab avalanche could result in injury or worse. Be particularly cautious in extreme terrain and on unsupported slopes where the consequences of an avalanche are elevated. It will also be important to keep an eye out for blowing snow today as winds increase out of the southwest. While minimal amounts of snow are available for transport, ridgetop winds are expected to reach as high as 80mph late this afternoon.  It may be possible to find areas where fresh wind slabs are depositing. 

advisory discussion

While generally, safe avalanche conditions exist it will not be impossible to find unstable snow today. Don’t be afraid to dig in and take a look at the snowpack below your feet. Pay attention to the weather and its effect on your local area and keep in mind that surface conditions are variable across the landscape.  Thin coverage, early season obstacles, and a variety of hard slick conditions have been reported throughout the range. Travel in many areas is difficult, and a fall in the wrong place could be unpleasant.   

recent observations
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12/19 - Magee Creek - slick surface conditions and pockets of unstable snow

12/19 - Bishop Creek - Open Water, low coverage, and variable surface conditions 

12/18 - Virginia Lakes - Sensitive Wind slab, Propagating ECT tests, Faceting grains

12/18 - Mammoth Area - Faceting grains and propagating ECT results in the Sherwins

12/18 - Mammoth Areas - Strong winds and faceting grains near the Mammoth crest

 

Weather and CURRENT CONDITIONS
weather summary

Expect partly cloudy skies and warmer temperatures today with highs above freezing near 10,000’.  Moderate southwest winds this morning are expected to increase throughout the day. Ridgetop gusts may reach as high as 80 mph by this evening. 

Winds will continue to increase throughout the day on Saturday and into Sunday in response to the incoming low-pressure trough. Models suggest we may start to see snow showers late on Saturday or early Sunday morning.  While snow totals are not expected to be huge, we can expect unsettled weather to continue through Christmas 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: Partly cloudy. Partly cloudy. Sunny.
Temperatures: 36 to 42. deg. F. 22 to 27. deg. F. 36 to 42. deg. F.
Mid Slope Winds: Southwest 15 to 25 mph with gusts to 65 mph. South 15 to 30 mph with gusts to 65 mph. South 15 to 30 mph with gusts to 75 mph.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy. Partly cloudy. Sunny.
Temperatures: 30 to 36. deg. F. 19 to 24. deg. F. 29 to 35. deg. F.
Ridge Top Winds: Southwest 20 to 30 mph with gusts to 50 mph increasing to 30 to 45 mph with gusts to 70 mph in the afternoon. Southwest 35 to 55 mph with gusts to 80 mph. Southwest 40 to 60 mph with gusts to 85 mph.
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 Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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