Avalanche Advisory: Sunday - Jan 28, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON January 29, 2018 @ 6:25 am
Avalanche Advisory published on January 28, 2018 @ 6:25 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

4-8” of cold wintry snow will warm today under sunny skies. Loose wet avalanches will become possible in terrain that warms quickly. Watch for signs of wet instability, such as rollerballs, near trees and rock outcrops, in bowls, and on steep sunny slopes at middle and lower elevations. Loose wet avalanches are most dangerous in or above terrain traps where even a small slide could carry you over a cliff or pile up deeply around you.

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

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.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Loose Wet
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Elevations below ~10,000’ will warm quickly today as winter weather transitions to high pressure and sunny skies. Cold wintry snow at the surface will warm and become moist, and in some cases for the first time. Small loose wet avalanches will become possible today on slopes that absorb the most solar energy. Lower elevations and easterly aspects will warm first, and then the warming will follow the sun around to the south and southwest as the day goes on. Watch for rollerballs and increasingly wet snow in rocky chutes, on tree covered slopes, and in cirques and bowls. Areas south of Mammoth may warm to higher elevations. Your best strategy for managing loose wet avalanches is your timing. If you can be off of solar heated slopes before they become too warm then you can avoid the problem all together.

Avalanche Problem 2: Persistent Slab
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Recent observations still show a persistent weak layer of sugary faceted grains lurking under our shallow snowpack. This layer has been seen 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. 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 is an indication of sudden collapse in this layer and should not be ignored. Digging down and looking at this layer is the best way to monitor what it can do on the slopes where you want to play.

advisory discussion

A few days of winter and a few inches of snow were a welcome change to the predominantly dry pattern this season. Cold winds redistributed new snow though yesterday morning into small shallow drifts on south and westerly aspects. And though ridgelines were scoured in many areas, lower down slopes still held soft wintry snow. But...

Resilient high pressure sets in over the region again today causing temperatures to rise above seasonal averages. Few clouds will impede the sun’s rays from beating down on the soft snow surface and light winds won’t do much to cool the snowpack below the Sierra Crest. Rocks and vegetation will heat the snow around them more quickly than open areas. Lower elevations will see faster warming that alpine slopes. Shift your attention towards rollerballs coming down the hill around you. Take note of how quickly the snow becomes moist, and of how deeply your feet sink into that wet snow. Large pinwheels of rolling snow, and sinking in to your boot tops indicate that the wet snow around you is losing strength. Timing is everything, and getting off of steep solar slopes before they get too warm is your best travel technique for dealing with loose wet 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.

Weather and CURRENT CONDITIONS
weather summary

High pressure will be the primary weather feature for the near future allowing for temperatures to increase well above seasonal averages. Light winds along the Sierra crest today into this evening as easterly flow compresses under the stable layer aloft along ridges. Gusts are not expected to be excessive, only in the 30 to 40 mph range. These winds will taper off overnight as the flow pattern shifts flow aloft slightly out of the south rather than the east.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Sunday Sunday Night Monday
Weather: Sunny. Clear. Partly cloudy.
Temperatures: 46 ti 52 deg. F. 27 to 35 deg. F. 46 to 54 deg. F.
Mid Slope Winds: Light winds. Light winds. Light winds.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Sunny. Clear. Partly cloudy then becoming mostly cloudy.
Temperatures: 38 to 43 deg. F. 29 to 34 deg. F. 39 to 45 deg. F.
Ridge Top Winds: NE Light winds. 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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