THIS AVALANCHE FORECAST EXPIRED ON February 23, 2018 @ 6:56 am
Avalanche Forecast published on February 22, 2018 @ 6:56 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger will exist today in most portions of the forecast area at all elevations. CONSIDERABLE avalanche danger may develop near treeline and above treeline in any areas that receive close to or more than a foot of new snow. Wind slabs are the main avalanche problem of concern. Isolated storm slabs may form in the areas of greatest new snow accumulation. Factor in how decreasing snow stability will affect travel plans and terrain selection as the day progresses.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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New wind slabs are expected to form this morning as SW winds drift new snow onto NW-N-NE-E-SE aspects in near treeline and above treeline terrain. Additional wind slab development is expected to occur this afternoon and evening with continued wind and snow showers. Avalanche size up to D2 (large enough to bury or injure a person) is possible today.

Identify and avoid areas of potentially unstable wind slab by looking for newly wind drifted snow. Slopes near or adjacent to a recent avalanche or those that have cornice features or wind pillows across the upper portion of the slope are the most suspect. Areas of snow surface cracking in near treeline and above treeline locations are an additional indication of unstable snow.

Avalanche Problem 2: Storm Slab
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This avalanche problem will be specific to areas that receive the upper end of forecast snowfall amounts of around a foot by this afternoon or evening. This problem will be unlikely on a regional scale today, but could be an issue in isolated areas.

Isolated storm slabs could become a problem today or tonight in wind protected areas below treeline that held snow cover prior to the current storm. This is mainly NW-N-NE-E aspects at the mid and upper elevations with very isolated distribution on all other aspects. This problem will be dependent on the formation of a weak layer within the storm snow that is deposited today. The period of snowfall at 2 inches per hour that is expected this morning followed by the second round of snowfall this afternoon and evening will be conducive to this type of potential weak layer formation. Avalanche size of D1 is most likely with size D2 possible in any areas that receive close to or more than a foot of new snow.

Avoid steep terrain in below treeline areas where any signs of instability have been observed. Human triggered snow surface cracking and/or recent avalanches are the easiest to identify signs of unstable snow.

 

recent observations
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* In most areas, the existing snowpack is in good condition to handle new snow loading. The one indication of exception to this was observed in the Carson Pass area on NE aspects between 8,600' and 8,800'. Around 1 foot or less below the old snow surface in this area, a thin crust with layers of faceted snow above and below it gave indications of a potentially problematic weak layer under new snow loading conditions.

* Snow cover remains thin at the lower elevations on all aspects and on most but not quite all mid and upper elevation SE-S-SW-W aspects. Mid and upper elevation NW-N-NE aspects hold a much deeper snowpack.

Weather and CURRENT CONDITIONS
weather summary

Two rounds of snowfall are forecast for today. The first is more consolidated and expected to occur between 6 am and 10 am with snowfall rates up to 2 inches per hour. The second round of snowfall will occur this afternoon and evening as snow showers. These snow showers could deposit significant amounts of snow in isolated areas, especially to the E and S of Lake Tahoe. Ridgetop winds from the SW increased yesterday afternoon and overnight and are now strong in speed. Strong to gale force winds are forecast to continue through this morning before easing to moderate speed this afternoon. Winds are forecast to shift to the NW tonight and eventually to the NE tomorrow and become light in speed. Air temperatures at the mid and upper elevations will remain below average with wind chill to -20 deg F today over the upper elevations.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 10 to 15 deg. F.
Max. temperature: 22 to 27 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 33 mph
Maximum ridgetop wind gust: 62 mph
New snowfall: Trace to 2 inches
Total snow depth: 30 to 51 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Cloudy skies with snow in the morning. Snow showers in the afternoon. Mostly cloudy skies. Widespread snow showers in the evening. Scattered snow showers after midnight. Partly cloudy skies with isolated snow showers.
Temperatures: 18 to 24 deg. F. 5 to 11 deg. F. 21 to 26 deg. F.
Mid Slope Winds: W W shifting to N NE
Wind Speed: 15 to 25 mph. Gusts to 60 mph decreasing to 40 mph in the afternoon. 10 to 15 mph with gusts up to 30 mph. Generally light winds. Gusts to 25 mph in the afternoon.
Expected snowfall: Likely 3 to 7 in. | Possible isolated areas of 7 to 12 Likely 1 to 4 in .| Small chance 4 to 6 0 to trace
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Cloudy skies with snow in the morning. Snow showers in the afternoon. Mostly cloudy skies. Widespread snow showers in the evening. Scattered snow showers after midnight. Partly cloudy skies with isolated snow showers.
Temperatures: 9 to 15 deg. F. 0 to 8 deg. F. 13 to 19 deg. F.
Ridge Top Winds: SW to W NW NE
Wind Speed: 25 to 40 mph with gusts to 80 mph, decreasing to 15 to 25 mph with gusts to 45 mph in the afternoon. 10 to 15 mph with gusts to 30 mph. 10 to 15 mph. Gusts up to 30 mph in the afternoon.
Expected snowfall: Likely 3 to 7 in. | Possible isolated areas of 7 to 12 Likely 1 to 4 in. | Small chance 4 to 6 0 to trace
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.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258