Avalanche Advisory: Monday - Jan 29, 2018

THIS AVALANCHE ADVISORY EXPIRED ON January 30, 2018 @ 6:35 am
Avalanche Advisory published on January 29, 2018 @ 6:35 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

Wet slab release may be possible today on south facing alpine slopes where previous northerly winds deposited drifts in the past few days. Loose wet avalanches are also possible as temperatures climb higher. Watch for signs of wet instability, such as rollerballs, near trees and rock outcrops on steep sunny slopes.

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: Wet Slab
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A skier-triggered avalanche yesterday in the Virginia Lakes area demonstrates that rapid warming can weaken the bonds between old wind slabs and the underlying snow. After northerly winds transported snow onto steep south facing alpine slopes Saturday, those very slopes were heated by unseasonable temperatures yesterday. And highs are forecast to be warmer today. Increasing clouds this afternoon could hold in the heat like a greenhouse. In some places (Virginia Lakes and June, for example) temperatures stayed relatively warm overnight and these areas could show more wet instability. Wet slabs become sensitive not because of new loading, but because heat can weaken the bonds in underlying weak 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 2: Loose Wet
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Sunny aspects where snow was previously soft and wintry at the surface will again warm and become moist by mid day and loose wet avalanches will become possible. 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 will be especially prone to wet instability. Increasing cloud cover may keep the heat in rather than let it escape back into the atmosphere. Watch for rollerballs and increasingly wet snow in rocky chutes, on tree covered slopes, 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 3: Persistent Slab
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That weak layer is still down there. Weak sugary snow has been observed between 50 and 70cm down on cooler northerly slopes near and below treeline in the Mammoth area and between 30 and 50cm down on similar aspects elsewhere. Some recent observations have even placed buried facets at 11,500’ on a north aspect. Test results throughout the season have shown this layer to fail under stress, but we have not seen enough of a slab on top of it to cause any avalanches yet. That doesn’t mean that triggering this layer is impossible, just unlikely. 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

Lots of people were out playing in the mountains yesterday enjoying the spring-like conditions. Things changed quickly and the snowpack became a patchwork of various avalanche problems, and more extreme warming will likely bring further change today. High pressure has settled in over California again and temperatures will climb even higher today than yesterday.

Transient northerly winds on Saturday blew soft wintry snow onto southerly aspects creating stubborn wind slabs on slopes where we don’t usually see them. Those same wind slabs became a problem for some skiers in Virginia Lakes yesterday as rapidly rising temperatures probably weakened the bonds holding the old slab to the underlying snow. Be aware, as things get even warmer today, of where previous wind loading has occurred under ridgelines and across steep gullies on southerly and easterly aspects. Increasing cloud cover may act as a reflector, bouncing solar radiation back down onto the snow and warming it further.

On solar slopes with soft, less cohesive snow, and especially near rocky outcrops and in cirques and gullies, loose wet avalanches will be possible as the sun melts the surface. 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.

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

recent observations
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1/28- Skier Triggered Slab Avalanche, Virginia Lakes

1/28- Warming and Transitional Snow Conditions, Red Cone

1/27- Wind Loading onto South Aspects, Red Cone and Hollywood Bowls

1/27- Wind Loading and Weak Layers, Virginia Lakes

1/27- Rollerballs, McGee Creek Chutes

 

Weather and CURRENT CONDITIONS
weather summary

The upper level ridge remains firmly in place bringing warmer than average temperatures for the near future. Breezy conditions can be expected Tuesday as a dry front passes by the region.

 

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. Mostly cloudy. Partly cloudy.
Temperatures: 47 to 53 deg. F. 26 to 32 deg. F. 50 to 58 deg. F.
Mid Slope Winds: Light becoming SW W W
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy. Mostly cloudy. Partly cloudy.
Temperatures: 40 to 45 deg. F. 24 to 29 deg. F. 44 to 50 deg. F.
Ridge Top Winds: Light becoming W W W
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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