Avalanche Advisory: Saturday - Feb 24, 2018

THIS AVALANCHE ADVISORY EXPIRED ON February 25, 2018 @ 6:59 am
Avalanche Advisory published on February 24, 2018 @ 6:59 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Fresh snow from Thursday along with shifting moderate to strong winds has led to pockets of CONSIDERABLE avalanche danger above tree-line due to scattered areas where wind deposited snow will likely be sensitive to human triggering.  Be on the lookout for consolidated wind deposited snow on all aspects.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

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.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

3-15” of light low-density snow fell Thursday into Thursday night, accompanied by strong SW winds.  Winds shifted out of the North yesterday, reaching strong levels by late afternoon, and now have shifted back out of the West for today, with gusts expected to reach 70mph.  Wind slabs with varying levels of sensitivity could be found on all aspects below ridgelines, across slopes on the leeward side of sub-ridges, and around other features that promote drifting,  A sizeable avalanche was triggered by skiers yesterday in Bloody Couloir.  Watch for signs such as shooting cracks from your skis as indications of unstable snow, and do your own localized assessments to determine if a slope is safe enough for you to ski or ride.     

advisory discussion

This has been a tricky period assigning Danger Ratings, with borderline significant snowfall amounts and cold very light low-density snow which has proven hard to predict how it will be deposited by moderate to strong shifting winds.  If MODERATE+ where an option, that would better fit the picture, as conditions are such that human triggered avalanches definitely seem likely, but are overall not as widespread as a solid CONSIDERABLE rating would suggest. 

3-15”+ of light low-density snow fell predominantly Thursday into Thursday night, accompanied by strong SW winds.  Sensors and reports indicate that the most snowfall was centered around the Mammoth region, with lesser amounts both north and south.  Winds decreased to just about calm by late Thursday night and began gradually increasing throughout the day Friday out of the North back to moderate and even strong levels at upper elevations.  Skiing conditions were fairly phenomenal on upper Mammoth Mtn yesterday, with some areas of knee-deep surprisingly unconsolidated snow.  One group of adventurous skiers triggered a sizeable avalanche at the top of the NE facing Bloody Couloir yesterday afternoon, with luckily no one being caught.  Wind transport was seen yesterday afternoon over ridgetops and across upper elevation ridges from Bishop north to VA Lakes.  While the predominant direction was out the N, one great example of terrain effects was seen over the Wheeler Crest where winds over the ridgetop were clearly transporting the snow from the N to the S, and just a couple hundred feet down slope, snow was being transported across the slope in the opposite direction.  These newly formed windslabs could be sitting on softer snow, or a thin layer of even weaker faceted snow in some areas.     

recent observations
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2/23:  Bloody Couloir - Skier triggered avalanche

2/23:  Mammoth Crest - Up to 50cm new snow, test results

2/23:  Mammoth - San Juaquin Ridge - Soft new windslabs

2/23:  VA Lakes - Wind transport, new snow

2/23:  Bishop to Mammoth - Visible wind transport

Weather and CURRENT CONDITIONS
weather summary

At the moment we are in between storms in our recent pattern of every few day inside-slider storms, until our next one is expected to hit Monday.

Expect partly couldy skies today, increasing west winds gusting up to 70mph by afternoon, and seasonably cold temps (but MUCH warmer than the single digits and teens of the past few days, with highs expected in the mid-20s around 10,000’).  Some isolated light upslope mountain snow showers could be possible this evening. 

Tomorrow (Sunday), should be 5 degrees warmer still, before another cold front/inside slider makes its way through Monday into Monday night, dropping temperatures again and bringing a few inches of snow.  Then a couple more days of dry weather before Thursday, when a more substantial storm looks possible with a much better moisture tap! 

      

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 Sunny
Temperatures: 27 to 33 deg. F. 8 to 13 deg. F. 32 to 38 deg. F.
Mid Slope Winds: West Northwest Southwest
Expected snowfall: 0 in. up to 2 in. o in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Partly cloudy Partly cloudy then becoming clear Sunny
Temperatures: 20 to 26 deg. F. 6 to 11 deg. F. 25 to 30 deg. F.
Ridge Top Winds: West Northwest Northwest shifting to southwest in the afternoon
Expected snowfall: 0 in. up to 2 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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