Eastern Sierra Avalanche Advisory - 1/15/18

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THIS AVALANCHE ADVISORY EXPIRED ON January 16, 2018 @ 6:29 am
Avalanche Advisory published on January 15, 2018 @ 6:29 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

The primary avalanche concern for Monday (1/15) continues to focus on the Persistent Slab problem created by several layers of weak faceted sugar snow within the snowpack.  Natural avalanches are unlikely, isolated triggered avalanches are possible today, especially on northerly aspects near and above treeline where the snow remains cold are the areas of greatest concern.  

Below ~9,000’, natural and triggered releases are unlikely due to thin snow coverage (below threshold).​

 

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

The primary concern continues to focus on the Persistent Slab problem created by the recent storm snow (1/9) followed by an wind event (1/10) that formed Wind Slabs, which are resting on a foundation of faceted sugar snow. Recent reports of Whumphing on northerly aspects in the mid-elevations highlights the potential for failure. If a failure occurs, it may propagate across the slope, possibly stepping down or eroding into the snowpack. Sudden collapsing is strong sign of instability. You will be most likely encounter this problem near and above treeline on northerly aspects, especially on recently wind loaded slopes.

Below ~9,000’- below threshold, natural and triggered releases are unlikely due to low snow coverage.​ 

advisory discussion

High-pressure makes its last stand today with another round of unseasonably warm temperatures before a return to more winter like weather and temperatures Tuesday. The mid-January sun is now strong enough to impart some heat into the snowpack. As a result, the snow at lower elevations has receded and thinned somewhat while mid and upper elevations solar aspects have developed a melt/freeze crust of varying thickness and maturity, depending on aspect, elevation, and solar exposure. The last significant snowfall was on 1/9, which brought ~ 1 -1.5’ of snow followed by a post-storm winds (Wednesday, 1/10) which formed stubborn Wind Slabs throughout the eastern Sierra, resulting in a small skier triggered release reported on the 11th near Crystal Lake as well as numerous naturals along the Crest and Virginia Lakes. Thursday, light snow showers moved into the region briefly along with moderate to strong Southwest winds leaving a dusting of snow in middle and upper elevations and a thin wind crust and Wind Slabs on cold northerly aspects and on shaded slopes. Since then, unseasonably warm temperatures have helped snow settlement. The complexity of the snowpack, especially on cooler northerly aspects, is further complicated by uneven patchy distribution of the early season snowpack. The deeper early season snowpack consists of alternating poorly bonded melt/freeze crusts and faceted sugar snow, which can be found below the recent snowfall (1/9) in the snowpack. Reports of Whumphing near Duck Pass illustrate the complexity of the snowpack and the varied spatial distribution of the Persistent Slab problem. The Persistent Slab problem will likely continue to be a concern for a while. With that in mind, it is important to assess the snow stability of the terrain before committing to ride. Evaluate the snow and terrain carefully and identify areas of concern.

 

Weather and CURRENT CONDITIONS
weather summary

Mon thru Tuesday - one last mild and dry day today (Monday) before the storm door finally opens with an initial storm late tonight and Tuesday morning. The system lacks a significant moisture tap and is rather weak compared to typical winter storm. The storm will track will favor the northern Sierras, so storm totals will be minimal, T to 2” with light Southwesterly winds and gusts of around 40-55 mph this afternoon, diminishing to 20-30 mph by Tuesday afternoon/evening. Precipitation with this storm will be over by Tuesday night.

Wed and beyond – Wednesday a brief break between storms. Increasing gusty winds across Sierra ridges to around 100 mph by late Wednesday as the jet stream shifts into CA/NV. A stronger storm system with a weak to moderate atmospheric river (AR) signature will move into the Sierra Thursday and Friday bringing snow to the Sierra. Winds gusts in the valleys of over 50 mph are likely with Sierra ridges seeing winds over 100 mph. This storm has the potential for 1 to 2 feet of snow in the High Sierra above 7000 ft. As the cold front pushes through the region, Thursday night into Friday morning, snow levels will fall to most valley floors. Blustery conditions and snow showers will remain through Friday. Colder temperatures remain in place through the weekend, with another strong winter storm system on the horizon for Sunday-Monday.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy then becoming mostly cloudy. Mostly cloudy. Slight chance of snow after midnight. Mostly cloudy. Chance of snow through the day. Slight chance of rain in the afternoon.
Temperatures: 46 to 54 deg. F. 30 to 35 deg. F. 39 to 47 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 10 to 15 mph with gusts to 35 mph. 10 to 15 mph with gusts to 45 mph. 15 to 25 mph with gusts to 50 mph.
Expected snowfall: 0 in. 0 in. up to 2 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy then becoming mostly cloudy. Mostly cloudy. Slight chance of snow after midnight. Mostly cloudy. Chance of snow.
Temperatures: 40 to 46 deg. F. 25 to 30 deg. F. 32 to 37 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 15 to 25 mph. Gusts up to 50 mph decreasing to 40 mph in the afternoon. 20 to 35 mph with gusts to 50 mph. 30 to 45 mph with gusts to 65 mph.
Expected snowfall: 0 in. 0 in. up to 2 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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