Avalanche Advisory: Tuesday - Jan 30, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON January 31, 2018 @ 6:22 am
Avalanche Advisory published on January 30, 2018 @ 6:22 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

Warm overnight lows and potentially record high temperatures today will keep the avalanche danger at moderate for wet instabilities. Loose wet avalanches are possible and a there may even be a few lingering wet slab avalanches waiting for you to trigger as the snow warms throughout the day. Note melting snow at the surface. Watch for rollerballs, on steep, rocky, and sunny slopes and time your day to avoid these areas as temperatures climb.

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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Several locations reported overnight lows above freezing on Sunday night. Hazy skies Monday intensified the surface radiation on most aspects. And last night, only a few places in the forecast area actually dipped below freezing for very long. As far as the snow is concerned it’s really warm. Potentially record highs today will continue this trend. Lower elevations and easterly aspects will warm first, and then the warming will rise even to alpine slopes and follow the sun around to the south and southwest as the day goes on. Areas that stayed relatively warm overnight, including some lower northerly slopes, will be especially prone to wet instability. Watch for rollerballs and increasingly wet snow in rocky chutes, where the snowpack is shallow, and in cirques and bowls. Timing is everything. Being out of steep sunny terrain in the heat of the day will allow you to avoid wet avalanche activity.

Avalanche Problem 2: Wet Slab
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Northerly wind on Saturday morning (1/27) deposited wind slabs high on southerly alpine slopes. These very slopes have been heating up ever since, melting the surface snow and percolating that water down where it can weaken the bonds in the underlying layers. A skier-triggered avalanche on Sunday in the Virginia Lakes area demonstrates that prolonged warming can tilt the scales in favor of slab release. Though isolated to a few alpine ridgelines, be aware of these old wind slabs as you travel down steep southerly slopes or under them. Wet slabs become sensitive not because of new loading, but because heat can weaken the bonds in underlying layers. So, your best strategy for managing wet avalanches is your timing. If you can be off of solar heated slopes before they become too warm then you can generally avoid the problem.

Avalanche Problem 3: Persistent Slab
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The thing about persistent weak layers is that they persist. And the weak sugary layers of facet snow, found between 30and 50cm down in our thin seasonal snowpack are still there. Some recent observations have even placed buried facets at 11,500’ on a north aspect. Test results are mixed about the potential for this layer to fail under stress. We have not seen a slab heavy enough to overpower the strength of this layer and cause any avalanches yet. But that doesn’t mean that triggering this layer is impossible, just unlikely, especially if the layer weakens. Any avalanche caused by the failure of this layer could be large. Whumphing and shooting cracks are a sure sign that sudden collapse in this layer is possible. Digging down and doing your own stability assessment is the best way to monitor what it can do on the slopes where you want to play.

advisory discussion

High pressure has settled in over California again and temperatures will climb even higher today than yesterday. Poor overnight freezing will continue to wreak havoc on our shallow snowpack. The snow surface will thaw a little more today creating wet avalanche problems where the melting is most intense. Melt water between snow grains dissolves the bonds that hold them together, like dipping a snow ball in a puddle. Wet snow that isn’t bonded in place can slide down steep slopes as loose wet, or even wet slab avalanches. Especially near rocky outcrops and in cirques and gullies, wet avalanches will be possible as the sun burns its way across the sky. Be attentive to rollerballs coming down the hill around you. They indicate that wet snow is loosing strength. Getting off of steep solar slopes before they get too warm is your best travel technique for dealing with wet snow avalanches.

Winds overnight were reliably of moderate intensity and from the west-southwest. These winds will continue into the afternoon as the Pacific Northwest gets another storm. Any new wind slab formation, however, would require upwind slopes to have significant snow available for transport onto easterly slopes. Release of new wind slabs would require poor bonding of the new slab with the underlying snow surface. It is not impossible for a few isolated ridgelines to develop a new wind slab today, but with warm temperatures all the way up into the alpine, the chances of that scenario seem dim. With any luck the wind will keep the snow surface a little cooler and prevent widespread melting.

Below ~9,000’ rocks and brush are still poking up from the surface and avalanches will have less snow to move down the hill.

Weather and CURRENT CONDITIONS
weather summary

A weak disturbance moving across the Pacific Northwest will bring moderate breezes today. And, potentially, record high temperatures. An upper level ridge off the west coast will keep conditions mostly dry with above average temperatures and generally light winds for the upcoming week.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy. Clear. Sunny.
Temperatures: 50 to 58 deg. F. 27 to 32 deg. F. 49 to 55 deg. F.
Mid Slope Winds: SW W W
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy. Clear. Sunny.
Temperatures: 44 to 50 deg. F. 25 to 30 deg. F. 42 to 47 deg. F.
Ridge Top Winds: W W NW
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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