THIS AVALANCHE ADVISORY EXPIRED ON February 9, 2016 @ 6:46 am
Avalanche Advisory published on February 8, 2016 @ 6:46 am
Issued by Brandon Schwartz - Tahoe National Forest

Early this morning, LOW avalanche danger exists for all elevations and aspects. Pockets of MODERATE avalanche danger will form quickly in response to daytime warming on E-SE-S-SW aspects at all elevations on slopes 35 degrees and steeper. On W-NW-N-NE aspects, avalanche danger will remain LOW. Isolated wind slabs may exist above treeline on S-SW-W-NW-N aspects, but are not expected to be a widespread avalanche problem today.

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    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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Air temperatures above 7,000' at 6 am this morning ranged from the upper 20s to mid 40s. In areas where air temperatures were at or above freezing, snow surface refreeze last night will have been entirely dependent on radiational cooling under clear skies. This superficial refreeze is expected to be a fairly thin in most areas and will melt quickly this morning.

The snowpack on E-SE-S-SW aspects remains in a transitional state. Under the relatively weaker and lower angle early February sun, daily melt-freeze cycles have been insufficient to produce corn snow conditions. What exists instead is a few inches of surface wet snow on top of colder, dry, less consolidated remnant storm snow, sitting on top of rain crust.

Once the thin ice layer of overnight snow surface refreeze is gone, marginally supportable conditions exist and the snowpack structure is conducive to human triggered loose wet avalanche activity. Snowpack failure has been occurring at the interface between the surface wet snow and the colder drier snow below it. In most areas this has manifested as human triggered roller balls and pinwheels. In more isolated areas human triggered loose wet avalanches large enough to bury or injure a person are possible in steep terrain. A few loose wet avalanches in recent days have been observed to entrain dry snow down to the rain crust, increasing the depth of debris piles.

The problematic surface wet snow over drier, colder snow structure is easily identified by hand pits as this structure exists within the top 6 to 8 inches of the snowpack in the vast majority of areas on E-SE-S-SW aspects. In areas where this snowpack structure exists, avoid travel on slopes steeper than 35 degrees and stay out from under steeper terrain above.

Avalanche Problem 2: Wind Slab
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Yesterday's stronger than forecast E winds were observed to transport snow in isolated areas above treeline. Some isolated small wind slabs may exist on S-SW-W-NW-N aspects today. This is not expected to be a widespread avalanche problem, but warrants some caution.

recent observations

Observations made and received yesterday from Castle Peak and Andesite Ridge (Donner Summit area), Jakes Peak (West Shore Tahoe area), and Echo Peak (Echo Summit area) all revealed similar conditions. A poor overnight snow surface refreeze had occurred and surface wet snow was widespread on E-SE-S-SW aspects by mid morning. Signs of recent loose wet instability existed in most areas. Most instability had taken the form of roller balls and pinwheels. Small to medium size loose wet avalanches that had occurred over the past 5 days were noted in steeper terrain. The marginally supportable upper snowpack structure of wet snow over dry snow over rain crust was observed on E-SE-S-SW aspects in all of these areas. Snow depth above the rain crust ranged from 2 to 10 inches deep. Yesterday's E winds were reported to have scoured down to and exposed the Jan 29 rain crust in some areas on N-NE-E aspects near and above treeline.

Weather and CURRENT CONDITIONS
weather summary

The ridge of high pressure over the region will shift to the east of the forecast area by this evening, shifting ridgetop wind direction and reducing wind speeds. Over the past 24 hours, ridgetop winds out of the E have greatly exceeded forecast wind speeds, holding in the strong range with the occasional gale force gust. Winds are expected to remain out of the E today and gradually decrease in speed through this evening. With the high pressure ridge axis movement, winds are forecast to shift to the south to southwest tonight and tomorrow. Generally light wind speeds will follow this directional shift. Air temperatures remain well above average, especially at the mid and upper elevations under inversion conditions. Some break down of the air temperature inversion is expected tonight and tomorrow following the change in wind direction. Remote sensors are reporting a wide range of air temperatures this morning above 8,000' ranging anywhere from the upper 20s to the upper 30s.

 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 26 to 37 deg. F.
Max. temperature in the last 24 hours: 38 to 44 deg. F.
Average wind direction during the last 24 hours: E
Average wind speed during the last 24 hours: 45 mph
Maximum wind gust in the last 24 hours: 74 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 66 to 81 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Sunny skies. Clear skies. Sunny skies.
Temperatures: 44 to 53 deg. F. 24 to 34 deg. F. 47 to 54 deg. F.
Wind Direction: E E S
Wind Speed: 15 to 20 mph with gusts to 30 mph. 10 to 15 mph in the evening, becoming light. 10 to 15 mph.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Sunny skies. Clear skies. Sunny skies.
Temperatures: 44 to 51 deg. F. 26 to 34 deg. F. 46 to 53 deg. F.
Wind Direction: E SE SW
Wind Speed: 35 to 40 mph with gusts to 55 mph, decreasing to 25 to 30 mph with gusts to 45 mph in the afternoon. 15 to 20 mph with gusts to 30 mph. 15 to 20 mph with gusts to 30 mph.
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This advisory covers the Central Sierra Nevada Mountains between Yuba Pass on the north and Ebbetts Pass on the south. Click here for a map of the forecast area. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.