Avalanche Advisory: Friday - Feb 16, 2018

THIS AVALANCHE ADVISORY EXPIRED ON February 17, 2018 @ 6:36 am
Avalanche Advisory published on February 16, 2018 @ 6:36 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

The avalanche danger is LOW today but that does not mean no danger. Small loose wet avalanches may be possible at lower elevations as the sun warms the snow and makes it wet. Watch for rollerballs originating from rocks and trees on steep sunny slopes by the afternoon. Isolated wind slabs may linger on alpine features that have promoted drifting in recent days. Be wary of shooting cracks and hollow sounding drifts just under cornices, on convexities, and in steep chutes.

1. Low

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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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Temperatures will jump up to 10 degrees warmer today and get well above freezing. Skies will be clear and winds light. The changes will be especially notable where lower elevation slopes are exposed to the sun. This will be the first time that the snow from early in the week warms appreciably and by the afternoon it may become wet and less stable. Melting will start on E aspects as the sun rises and follow it across S and then W facing slopes. Rock outcrops and vegetation will help heat the snow around them even more. Rollerballs and even some small loose wet avalanche activity is possible today. Areas with a thinner snow cover will warm first, but have less snow to slide down the hill. Even small loose wet avalanches can be dangerous if they carry you into a terrain trap or into obstacles where you could get hurt.

Avalanche Problem 2: Wind Slab
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Wind slabs formed throughout this past week with the passage of a cold front sliding down the east side of the Sierra. Winds shifted from N to SW to N again with each round carrying snow onto leeward alpine slopes. Temperatures have been pretty cold until today, so wind slabs have been gaining strength slowly. Isolated features may still hold lingering wind drifts that are just sensitive enough for you to trigger today. Be aware of steep, consequential, alpine slopes with round pillowy drifts, especially just below corniced ridges and near the sidewalls of gullies.

advisory discussion

4-8” of very light and cold snow fell on Monday and the changing winds have been redistributing it ever since. Wind drifts have been found on favorable alpine features on many aspects. Many of these older wind slabs have gained strength and would be very difficult to trigger. But the recent cold temperatures may have slowed the bonding between old snow and slab in a few locations. If you decide to play in steep terrain above treeline today you should be aware of where snow has previously drifted. Hollow sounding drifts, or denser snow that cracks around you means that wind slabs may still fail under your weight. You’re most likely to find these slabs at high elevations just under cornices, in the tops of chutes, and on the steepest part of convexities.

On sheltered and lower elevation slopes the storm snow is largely undisturbed. It’s soft and lacks cohesion. That means that as temperatures climb up to well above freezing today you may find sunny slopes are becoming wet and less stable. Pay attention to rollerballs and small point releases originating from rocky outcrops or cliff bands and under trees. These indicate that the sun is heating the snow and the risk of loose wet avalanches is increasing. Though the danger is not expected to be very high, it will rise as the sun heats E facing slopes in the morning and then follow it across S and SW facing slopes by late afternoon.

Hard surfaces like wind board, crusts, and ice all make for treacherous conditions in the event of a fall. Ice axes and crampons are a good idea if you plan to venture into steep or consequential terrain today.

Weather and CURRENT CONDITIONS
weather summary

Temperatures will continue to increase today and Saturday as building high pressure off the coast allows warmer air to move back into the region from the southwest. Dry northerly flow aloft will keep skies clear and winds generally calm through Saturday morning.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Friday Friday Night Saturday
Weather: Sunny. Clear. Sunny.
Temperatures: 37 to 45 deg. F. 22 to 27 deg. F. 40 to 48 deg. F.
Wind Direction: Light winds. Light winds. SW
Wind Speed: Light winds. Light winds. Light becoming 10 to 15 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Sunny. Clear. Sunny.
Temperatures: 31 to 37 deg. F. 19 to 24 deg. F. 32 to 40 deg. F.
Wind Direction: W N SW
Wind Speed: 10 to 15 mph. Gusts up to 25 mph in the morning. 10 to 15 mph in the evening becoming light. 10 to 15 mph with gusts to 25 mph in the afternoon.
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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