THIS AVALANCHE ADVISORY EXPIRED ON February 28, 2017 @ 6:45 am
Avalanche Advisory published on February 27, 2017 @ 6:45 am
Issued by Steve Reynaud - Tahoe National Forest

Considerable avalanche danger exists in near treeline and above treeline areas due to wind slab avalanchesModerate avalanche danger exists near and below treeline due to storm slab avalanches.  Natural and human triggered avalanches are likely today.  Cautious route finding and conservative decision making are essential.

3. Considerable

?

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

3. Considerable

?

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

2. Moderate

?

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Gale force SW/W winds with additional new snow overnight will create wind slabs on NW-N-NE-E-SE-S aspects in near and above treeline areas.  Natural and human triggered wind slab avalanches will be likely today.  Small wind slabs were very reactive yesterday with wide propagation occurring as the storm moved into the area.  Large cornices exist along ridgelines and represent a significant risk to backcountry travelers.  Look for blowing snow, cornice formation, and wind pillows.  Avoid steep wind loaded terrain.   

Avalanche Problem 2: Storm Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Storm slabs will be possible on all aspects near treeline and below treeline in wind protected terrain.  These storm slabs are expected to be under 1' deep and to have poor bonding at the new snow/old snow interface.  Cold temperatures will further slow down the bonding process of this new snow and there is also the possibility that this new snow has buried a layer of surface hoar in open, wind protected, below treeline areas.  

Look for cracking around skis.  Use small test slopes and hand pits to gather more information about the storm snow.  Avoid slopes with unstable snow.

recent observations

Observations were made and received yesterday from Shallenberger Ridge (Donner Summit area), Carpenter Peak (Independence Lake area), Indian Valley (Ebbetts Pass area), and Echo Peak (Echo Pass area).  Avalanches were reported from Carpenter Peak and Echo Peak.  Small wind slabs were forming on Carpenter Peak with test slopes showing wind slab avalanches 2-6'' deep with wide propagation.  On Echo Peak, a cornice failure caused a wind slab to fail and run downslope over benches into lower angle terrain.  Surface hoar was reported in the Donner Summit area between 6500-7300' on N-NE aspects.

Weather and CURRENT CONDITIONS
weather summary

3 to 7'' of new snow overnight with light snow showers forecasted to continue into Tuesday.  An additional 3'' of snow is possible from Tahoe southward throughout today.  SW/W winds along the Sierra Crest overnight were 40 to 60mph with gusts over 100mph.  Winds should decrease into the afternoon today but will still be in the strong range.  High pressure will slowly build into the area with lighter winds and warming temperatures starting Wednesday.  The next chance of a storm will be over the weekend.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 10 to 15 deg. F.
Max. temperature in the last 24 hours: 28 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 40 to 60 mph
Maximum wind gust in the last 24 hours: 119 mph
New snowfall in the last 24 hours: 3 to 7 inches
Total snow depth: 142 to 196 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy. Snow showers possible in the morning, then scattered snow showers in the afternoon. Mostly cloudy. Slight chance of snow showers. Partly cloudy then becoming sunny.
Temperatures: 22 to 27 deg. F. 6 to 16 deg. F. 29 to 34 deg. F.
Wind Direction: W W NW
Wind Speed: 15 to 20mph. Gusts up to 45mph decreasing to 30 in the afternoon. 10 to 15mph with gusts to 25mph becoming light in the evening. Light winds
Expected snowfall: Up to 2 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy. Snow likely in the morning then scattered snow showers in the afternoon. Mostly cloudy. Slight chance of snow showers. Partly cloudy then becoming sunny.
Temperatures: 17 to 23 deg. F. 6 to 14 deg. F. 27 to 32 deg. F.
Wind Direction: W SW NW
Wind Speed: 25 to 45mph with gusts to 85mph decreasing to 15 to 20mph with gusts to 40mph in the afternoon. 10 to 15mph with gusts to 30mph. 10 to 15mph with gusts to 35mph.
Expected snowfall: Up to 2 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.

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