Avalanche Advisory: Wednesday - Jan 31, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON February 1, 2018 @ 6:43 am
Avalanche Advisory published on January 31, 2018 @ 6:43 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

Wednesday (1/31) - primary avalanche concern will focus on wet instabilities. With overnight temperatures hovering near or above freezing and another round of above seasonal highs for today, the avalanche danger will remain at moderate for Loose Wet avalanches with the remote possibility of Wet Slabs. Monitor surface snow for excessive thawing. Avoid steep, rocky, and sunny slopes as temperatures climb through the day.

Below ~9,000’, natural and triggered releases are unlikely due to thin and well-anchored 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: Loose Wet
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Today (Wednesday), with lows hovering near or above freezing overnight and unseasonably warm temperatures forecasted for today, the primary avalanche problem will focus on Loose Wet avalanches. Given the weak freeze overnight, you can anticipate lower elevations and easterly aspects thawing quickly, followed by the Alpine as the sun begins to warm solar aspects through the day. Areas that stayed above freezing, including some lower elevation northerly terrain, will be especially prone to wet instability. Watch for rollerballing and increasingly wet snow around rocky features and chutes where the snowpack is shallow. Time your travels to be out of steep sunny terrain before the snow thaws from the heat of the day. 

Avalanche Problem 2: Wet Slab
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Saturday (1/27), northerly winds produced Wind Slabs on southerly alpine slopes. As these slopes heat up, the surface snow thaws, potentially allowing water to percolate down into the snowpack and weakening the bonds to the underlying layers as demonstrated by a skier-triggered avalanche in the Virginia Lakes. This problem is primarily isolated to alpine ridgelines where these old Wind Slabs have formed. Wet Slabs failures are a result of water and heat breaking down the bonds to the underlying layers. Time your travels to be out of steep sunny terrain before the snow thaws from the heat of the day.

 

 

Avalanche Problem 3: Persistent Slab
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Patchy Persistent Slab issues continue to lurk within the snowpack with weak faceted sugar layers down about 30 to 50cm from the surface. Distribution is primarily confined to NE-N-NW aspects from ~9500’ to as high as ~11,500’. Test results continue to be mixed and relatively non-reactive. Despite the persistent weakness, there haven’t been any recent reports of this layer failing but a triggered release is possible, though unlikely. Whumphing and shooting cracks are signs that sudden collapse is possible. Perform your own stability tests to assess the snowpack of the slope you want to ride.

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

advisory discussion

Dry and dusty conditions (high pressure) continues to dominate California’s weather with unseasonably warm temperatures and weak overnight freezes while deflecting storm systems well to the north. As the sun thaws the surface snow, the free water breaks down the bonds between snow grains and layers within the snowpack. As this process continues, the snow looses internal strength and cohesion; the mass of the snow exceeds the snow strength, resulting in a Wet Loose or Wet Slab avalanche. Rocky terrain features can introduce tremendous amounts of heat into the snowpack and cause localized rapid thawing in cirques and gullies. While traveling, watch out for rollerballing, they’re an indicator the snow is loosing strength. Time your travels to be out of steep sunny terrain before the snow thaws from the heat of the day.

Moderate SW winds overnight may have formed isolated Wind Slabs on NW-N-NE aspects in the Alpine where there remains significant snow is available for transport but this prospect is not likely. The moderate winds should help keep the snow surface a little cooler and possibly helpreduce widespread melting.

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

Weather and CURRENT CONDITIONS
weather summary

Wed thru Saturday - A ridge near/off the coast will be the dominant player for the next 10 days. A weak short wave will move into Oregon on Thursday, and will bring some increased cloud cover with limited showers near the Oregon Border. Highs in the 50s in the Sierra will be common. Friday into Saturday, the flow aloft becomes more north to northwest with northeast surface winds, resulting in slight cooling.

 

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: Sunny. Partly cloudy then becoming mostly cloudy. Mostly cloudy.
Temperatures: 50 to 56 deg. F. 29 to 34 deg. F. 46 to 54 deg. F.
Mid Slope Winds: West Light winds. Light winds.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Sunny. Partly cloudy then becoming mostly cloudy. Mostly cloudy.
Temperatures: 43 to 48 deg. F. 26 to 31 deg. F. 39 to 45 deg. F.
Ridge Top Winds: West Northwest West
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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