THIS AVALANCHE ADVISORY EXPIRED ON February 19, 2018 @ 6:48 am
Avalanche Advisory published on February 18, 2018 @ 6:48 am
Issued by Andy Anderson - Tahoe National Forest

The avalanche danger will remain LOW for all elevations for most of the day. As new snow accumulates this evening and overnight the avalanche danger will increase to MODERATE in near and above treeline terrain due to newly formed wind slabs. In addition, dangerously cold temperatures with wind chills below zero could pose problems for anyone out in the backcountry tonight. 

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.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Avalanches will remain unlikely until new snow starts to accumulate later today and this evening. Other hazards including long sliding falls on frozen icy crusts and collisions with exposed obstacles (or both) still exist. Strong winds before and during the storm and falling temperatures with wind chills that become dangerously cold could also pose threats to backcountry travelers especially those planning to spend the night outside. 

Once new snow starts to accumulate this afternoon and evening, the avalanche danger will start to increase. New fragile wind slabs will form on wind-loaded N-NE-E aspects and cross-loaded NW and SE aspects in near and above treeline terrain. These wind slabs will start small and will grow in size as the snow accumulates. In the most heavily wind-loaded areas that receive the most new snow, they could grow large enough that avalanches involving these wind slabs could bury or injure a person this evening and during the night (or earlier if the snow arrives sooner than expected).

If the frigid single-digit temperatures with wind chills below zero and winds gusting to ~100 mph are not enough to deter a person from backcountry travel tonight, then expect human triggered wind slab avalanches to become possible in wind-loaded areas this evening and during the night as well. 

recent observations

* Observations yesterday from Chickadee Ridge (Mt. Rose backcountry) showed minor isolated, inconsequential wind slabs on some leeward slopes near ridgelines. Snow surfaces ranged from firm crusts in wind and/or sun exposed areas to soft snow in shaded wind protected areas. Snowpit data from this area indicated a well-consolidated snowpack below the surface. This data is consistent with other observations across the forecast area in the last several days.

* Recent strong winds have scoured many exposed near and above treeline slopes down to firm crusts.

* Thin snow cover conditions exist throughout the forecast area on all aspects at lower elevations. Thin snow cover or bare ground exists on most sun-exposed aspects at all elevations with a few notable exceptions.

Weather and CURRENT CONDITIONS
weather summary

Southwest winds started increasing yesterday afternoon and continued to gain strength through the night. The winds should remain strong with gusts up to 115 mph along the ridgetops today as a strong arctic cold front moves into the area. By this afternoon This cold front will bring frigid temperatures and some snow to the area once it arrives this afternoon and evening. The forecast calls for single digit lows with wind chills well below 0 and 3 to 6 inches of new snow accumulation by tomorrow afternoon. Most of this snow should fall this evening and tonight. This fast-moving system should progress out of the area tomorrow leaving the cold arctic temperatures and NW winds in its wake. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 23 to 31 deg. F.
Max. temperature in the last 24 hours: 43 to 49 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: Yesterday: 15 to 25 mph | Last night: 40 to 50 mph
Maximum wind gust in the last 24 hours: 100 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 27 to 48 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy becoming mostly cloudy with snow showers likely later this afternoon. Mostly cloudy with snow showers in the evening and snow showers likely after midnight Mostly cloudy with snow showers likely
Temperatures: 32 to 37 deg. F. 8 to 13 deg. F. 16 to 21 deg. F.
Wind Direction: Southwest West Northwest
Wind Speed: 20 to 30 mph with gusts to 75 mph decreasing to 60 mph in the afternoon 20 to 30 mph with gusts to 60 mph decreasing to 50 mph after midnight 15 to 20 mph with gusts to 40 mph
Expected snowfall: up to 1 in. 1 to 4 in. 1 to 3 in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy becoming mostly cloudy with snow showers likely later this afternoon. Mostly cloudy with snow showers in the evening and snow showers likely after midnight Mostly cloudy with snow showers likely
Temperatures: 27 to 33 deg. F. 3 to 9 deg. F. 10 to 16 deg. F.
Wind Direction: Southwest West Northwest
Wind Speed: 35 to 55 mph with gusts to 115 mph decreasing to 95 mph in the afternoon. 30 to 45 mph with gusts to 95 mph decreasing to 20 to 35 mph with gusts to 60 mph after midnight 20 to 30 mph with gusts to 50 mph decreasing 35 mph in the afternoon.
Expected snowfall: up to 1 in. 2 to 4 in. 1 to 3 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