Avalanche Advisory: Wednesday - Feb 21, 2018

THIS AVALANCHE ADVISORY EXPIRED ON February 22, 2018 @ 6:35 am
Avalanche Advisory published on February 21, 2018 @ 6:35 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

MODERATE avalanche danger will exist in steep terrain above treeline today due to recent wind slab formation. The avalanche danger near and below treeline is rated LOW, but be on the lookout for unstable wind deposits on isolated features.

Slide-for-life conditions and obstacles are an additional concern.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

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.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
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    Very Large
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    Small

Southwest Winds picked up around noon yesterday at upper elevations in the Mammoth area and had a few inches of light storm snow to redistribute onto leeward slopes. Ridgetop winds appear to have continued at moderate speeds into early this morning before becoming light. Small and isolated wind slabs were observed to be reactive yesterday afternoon along the Mammoth Crest and in Virginia Lakes. The cold temperatures will slow the bonding of these newly formed drifts. Watch for areas in steep alpine terrain that have recently favored formation of denser wind deposits that can crack around you. The sidewalls of gullies and the tops of chutes steeper than about 35 degrees are the most likely places to find wind slabs that may still be sensitive enough for human triggering today. In areas with big fetches, where winds have larger sources of snow to draw from, wind slabs could be larger.

advisory discussion

Another “inside slider” storm with little moisture made its way down the Sierra Sunday night dropping 3-4” of light new snow. The cold wind that accompanied this storm seemed to have only isolated effects on the new snow by Monday. Yesterday afternoon, however, as winds increased to ideal snow transport speeds at upper elevations, sensitive wind slabs formed on NE facing features in the Mammoth and Virginia Lakes areas. Light snow showers yesterday dropped an additional 1” or so for the winds to play with. With limited observations coming in to prove otherwise, wind slabs are expected to have formed on favored alpine terrain features elsewhere in the forecast zone as well.

Winds dropped off to light early this morning, but cold temperatures will slow the bonding of recently formed slabs and they may still be reactive or even touchy to human triggers today.

If the winds pick up again this evening with the chance of additional snowfall we may see another round of wind loading before tomorrow.

recent observations
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2/20- Small Isolated Wind Slabs, Virginia Lakes

2/20- Intentional Skier Triggered Wind Slab Avalanche, Mammoth Crest

 

Weather and CURRENT CONDITIONS
weather summary

Winter weather will continue to impact the region with scattered snow showers bringing up to 1” of new snow and light winds today. A series of cold winter storms will continue to affect the area through at least next week. The first tonight through Thursday will likely bring widespread light to moderate snowfall throughout the region. Most areas will see a break in snowfall through the weekend with a another stronger storm possible Monday/Tuesday next week.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Scattered snow showers. Mostly cloudy then becoming partly cloudy. Isolated snow showers through the night. Mostly cloudy. Widespread snow showers.
Temperatures: 12 to 22 deg. F. 0 to 10 deg. F. 5 to 15 deg. F.
Mid Slope Winds: Light winds. Light winds. SW
Expected snowfall: 80% probability...up to 1 inch. 20% probability...0 in. 80% probability...up to 1 inch. 20% probability...0 in. 70% probability...of 1 to 5 inches. 30% probability...of 6 to 10 in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Scattered snow showers. Mostly cloudy then becoming partly cloudy. Scattered snow showers. Mostly cloudy. Widespread snow showers.
Temperatures: 8 to 13 deg. F. -4 to 7 deg. F. 0 to 10 deg. F.
Ridge Top Winds: Light winds. SW SW
Expected snowfall: 80% probability...up to 1 inch. 20% probability...0 in. 80% probability...up to 1 inch. 20% probability...0 in. 70% probability...of 2 to 6 inches. 30% probability...of 7 to 12 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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