THIS AVALANCHE FORECAST EXPIRED ON January 12, 2016 @ 6:57 am
Avalanche Forecast published on January 11, 2016 @ 6:57 am
Issued by Brandon Schwartz - Tahoe National Forest

Unusual avalanche conditions persist with pockets of MODERATE avalanche danger in open areas at and below treeline on N-NE-E-SE aspects on slopes 35 degrees and steeper. Persistent slabs associated with the Jan 5 buried surface hoar layer exist in some areas. Where this weak layer is absent, LOW avalanche danger exists. Avoid steep terrain adjacent to areas of recent avalanche activity, even if the crown and debris are covered under a couple inches of new snow and now look old.

1. Low

?

Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

2. Moderate

?

Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

?

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

The Jan 5 surface hoar layer buried 1 to 1.5 feet deep in the snowpack has been reactive since Tuesday in the areas where it exists. Buried surface hoar is an uncommon weak layer for this region. This weak layer has been very slow to stabilize. It is now one week old and day to day snowpit data continues to identify ongoing problems. This weak layer is certainly not abiding by any mythical "24 hour rule". Have a look below at the snowpit videos taken from a Level II avalanche class yesterday on Andesite Ridge (Donner Summit area) to see examples of unstable, propagating test results.

Currently, the areas where avalanches are most likely to be triggered are not in the traditional wind loaded zones along the ridgelines, but in steep open areas at treeline and below treeline on N-NE-E aspects and possibly SE aspects. Have a conversation with your travel partner(s) and make sure everyone understands that this is an at treeline and below treeline problem. Shift the focus from the traditional wind loaded avalanche start zones up high to the steep wind protected open areas lower down on the mountain.

This weak layer does not exist or is not reactive in all areas. Don't let a lack of evidence of instability in one portion of the forecast area affect how decisions are made when moving to another part of the forecast area. Continue to search out signs of instability including recent avalanche activity, even if it "looks old" buried under an inch or two of recent snowfall. If you see evidence of recent avalanche activity, there is a good chance that the buried surface hoar exists in the area. Snowpit data is very helpful, but it has to come from the right locations and it never proves stability.  If in doubt, stick to slopes less than 32 degrees in steepness. Use an analog inclinometer or smartphone app to measure slope angles rather than guessing.

Forecast discussion

A few tiny wind deposits were reported yesterday in above treeline terrain. Some skier triggered cracking was noted, but slabs were too small for any dangerous avalanche activity to occur. Some small amount of additional wind transport is possible today above treeline, but significant new wind slab formation is unlikely.

recent observations

Snowpit data made and received from around the forecast area indicates ongoing instability problems in locations where the Jan 5 buried surface hoar layer exists. Where this layer is absent, the snowpack is well bonded and consolidated, with no evidence of instability. Problematic buried surface hoar is known to exist in various locations in the Donner Summit area and in some but not all locations in the Carson Pass area. Observations targeted at finding the Jan 5 buried surface hoar layer over the past few days have indicated an absence of this layer around Barker Pass and Peak (Blackwood Canyon area), on Echo Peak (Echo Summit area), on Jakes Peak (West Shore Tahoe area), and on Mt. Tallac (Desolation Wilderness area). Specific observations have not been made in the Mount Rose area, but no reports of buried surface hoar have been received.

Skier and snowboarder triggered avalanches were reported on Thursday on Andesite Ridge (Donner Summit area) and on Thursday and Friday on Red Lake Peak (Carson Pass area). In both cases avalanches occurred in steep open terrain near treeline to below treeline on NE to E aspects. Snowpack failure occurred 1 to 1.5 below the snow surface at the base of the recent storm snow accumulated since Jan 5.

Weather and CURRENT CONDITIONS
weather summary

High pressure remains the dominate feature over the region through Tuesday. A weather system passing to the north will spread some cloud cover over the forecast area today and provide a slight increase to W winds. Otherwise, air temperature inversion conditions are expected to continue to build. Maximum daytime air temperatures for areas above 7,000' are forecast to reach the upper 20s to upper 30s today. Ridgetop winds are out of the SW this morning and are increasing in speed. Light to moderate speed W winds are forecast for today over the mid and upper elevations. For Tuesday expect decreasing cloud cover, near to above freezing air temperatures, and light to moderate speed SW winds.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 19 to 29 deg. F.
Max. temperature in the last 24 hours: 29 to 32 deg. F.
Average wind direction during the last 24 hours: Variable
Average wind speed during the last 24 hours: 17 mph
Maximum wind gust in the last 24 hours: 46 mph
New snowfall in the last 24 hours: 0 to trace inches
Total snow depth: 48 to 58 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 skies. Mostly cloudy skies, becoming partly cloudy. Partly cloudy skies.
Temperatures: 29 to 36 deg. F. 14 to 24 deg. F. 31 to 38 deg. F.
Winds: W SW S
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy skies. Mostly cloudy skies, becoming partly cloudy. Partly cloudy skies.
Temperatures: 31 to 38 deg. F. 14 to 21 deg. F. 31 to 38 deg. F.
Winds: W SW SW
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.