THIS AVALANCHE ADVISORY EXPIRED ON March 18, 2015 @ 6:51 am
Avalanche Advisory published on March 17, 2015 @ 6:51 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger will exist at all elevations and on all aspects on slopes 37 degrees and steeper. Human triggered loose wet avalanches remain possible today. Some wet slab avalanches may also become possible on isolated terrain features where wet snow exists above an impermeable bed surface. Since most of the snow has melted away from the SE-S-SW-W aspects, wet snow instabilities on these aspects will remain limited to the isolated slopes that still have snow cover.

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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Last night temperatures cooled a few degrees compared to previous nights and dipped into the mid to upper 30's above 8000 ft. and upper 30's and low 40's below 8000 ft. These still above freezing temps and the more consistent blanket of cloud cover last night should have prevented the snowpack from undergoing much of a refreeze in most areas. Some places may have experienced a weak refreeze in areas where pockets of colder air existed. Since the cloud cover should start to dissipate today and temperatures should rise into the upper 40's again, any refreeze that did form last night should quickly melt leaving wet snow in any areas where snow exists. Human triggered loose wet avalanches will remain possible today on all aspects on slopes 37 degrees and steeper.

Since most of the snow has melted away from the SE-S-SW-W aspects, wet snow instabilities will remain confined to the isolated areas where snow cover exists on these aspects. NW-N-NE-E aspects hold the best chances for finding wet snow instabilities today since snow cover remains more consistent on those aspects. Even though these kind of avalanches may not involve enough snow to bury a person, they can push people into areas that would have serious consequences. Keep in mind that secondary terrain hazards such as cliffs and terrain traps hold the potential to greatly magnify consequences of an avalanche that would otherwise be too small to bury or injure a person.

Avalanche Problem 2: Wet Slab
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Wet slab avalanches still remain unlikely in most places, but 4 nights in a row without a solid refreeze, another day of warm weather, and deep wet snow on all aspects where snow exists means that wet slab avalanches may become possible on isolated terrain features. Since the snowpack has already been through so many melt-freeze cycles this year, the potential for these kind of avalanches should remain confined to isolated areas where the most wet snow exists and where a good bed surface (like a granite slab) exists below the wet snow. Use clues like shin deep wet snow and loose wet snow instabilities to help decide when to leave the snow and head for other activities.

recent observations

Yesterday observations on Relay Peak showed variable wet snow and melt-freeze conditions on all aspects. Some E-SE aspects held corn conditions with a few inches of wet melt-freeze snow resting on top of a barely supportable melt-freeze crust with more wet snow below it. 10 to 18 inches of unsupportable wet snow existed on other E-SE aspects. N-NE aspects held 10 to 20 inches of wet sticky snow that has not transitioned to corn with old well bonded snow below it. Human triggered pinwheels up to 18-20 inches in diameter occurred on N-NE facing test slopes up to 9800 ft. One small skier triggered collapse about 3-4 ft. in diameter occurred on a low angle S facing slope at 9100 ft.

Weather and CURRENT CONDITIONS
weather summary

Cloudy and unsettled weather should persist across the region today due to two small low pressure systems passing by the fringes of the forecast area. As the one to the north of the area moves farther east this afternoon, cloud cover over the northern part of the forecast area should start to diminish. Another small low pressure forming over central Nevada should keep more clouds over the southern part of the forecast area. These systems will provide a slight chance of showers north of I-80 and south of Hwy 50 today. Tomorrow the second low over Nevada will allow for a slight chance of afternoon showers/thunderstorms. Temperatures should remain warm snow levels will remain above 8000 ft. The winds should continue to decrease today and should shift from the southwest to the north and east and become light by tomorrow afternoon.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 31 to 39 deg. F.
Max. temperature in the last 24 hours: 44 to 50 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 20 mph
Maximum wind gust in the last 24 hours: 55 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 21 to 41 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy becoming partly cloudy this afternoon. Slight chance of rain showers this afternoon. Partly cloudy Partly cloudy with a slight chance of rain showers and thunderstorms in the afternoon
Temperatures: 44 to 51 deg. F. 26 to 33 deg. F. 44 to 51 deg. F.
Wind Direction: Southwest Northwest Variable
Wind Speed: 15 to 20 mph with gusts to 30 mph 10 to 15 mph with gusts to 25 mph in the evening becoming light over night Light
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy becoming partly cloudy this afternoon. Slight chance of rain showers this afternoon. Partly cloudy Partly cloudy with a slight chance of rain showers and thunderstorms in the afternoon
Temperatures: 43 to 49 deg. F. 24 to 31 deg. F. 44 to 50 deg. F.
Wind Direction: Southwest Northwest shifting to the northeast after midnight East
Wind Speed: 30 to 35 mph with gusts to 50 mph decreasing to 20 to 25 mph with gusts to 40 mph in the afternoon 15 to 20 mph with gusts to 30 mph 10 to 15 mph in the morning becoming light in the afternoon
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.