THIS AVALANCHE ADVISORY EXPIRED ON January 3, 2014 @ 6:00 am
Avalanche Advisory published on January 2, 2014 @ 6:00 am
Issued by Brandon Schwartz - Tahoe National Forest

Pockets of  MODERATE avalanche danger remain near and below treeline on NW-N-NE aspects on slopes steeper than 32 degrees where consistent snow cover exists. Lingering persistent slabs are keeping the possibility of human triggered avalanches ongoing in certain areas near treeline and below treeline on NW-N-NE aspects. For all other areas avalanche danger is either LOW or non-existent due to the lack of snow cover.

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

Variability in avalanche danger exists around the forecast area. Persistent slabs linger in some areas near treeline and below treeline on NW-N-NE aspects due to the presence of the faceted Dec 7 persistent weak layer. Field observations of the past 3+ weeks have shown the greatest amount of ongoing instability with little to no week to week stability improvement in the Carson Pass and Pole Creek/Deep Creek areas. Observations from the Mount Rose, Donner Summit, West Shore Tahoe, and Echo Summit areas have shown significantly less ongiong instability and in some cases stable conditions near treeline and below treeline on NW-N-NE aspects.

Triggering and going for a short ride in even a small avalanche at this time will almost certainly have significantly elevated consequences due to the almost guaranteed impact with rocks, logs, or trees due to the shallow snowpack. Becoming caught in the same size avalanche above a more typical deep Sierra snowpack could very well have minimal consequences.

recent observations

Observations made just two days ago on Dec 31 showed significant ongoing snowpack instability in the Carson Pass area. Travel on near treeline and below treeline N-NE aspects in the area south of Red Lake produced cracking and collapsing of the snowpack. Some of the collapses occurred on the same slopes and areas previously collapsed by the same forecaster traveling through the area on Dec 12. Click here and watch the video showing very impressive collapse and propagation of the faceted Dec 7 persistent weak layer along a 2 meter (6.6ft) wide extended column test in this area just two days ago. It is an excellent illustrator of the ongoing snowpack instability.

Avalanche danger on SE-S-SW-W aspects has been mostly eliminated due to melt. Some snow cover exists on E aspects, but the Dec 7 facet layer has not been observed at any elevation on E aspects. The Dec 7 facet layer is also absent above treeline on NW-N-NE aspects. This is allowing for LOW avalanche danger in these areas. Near treeline and below treeline on NW-N-NE aspects, continued snowpack settlement has reduced the overall snowpack height and allowed rocks, logs, and stumps to show through the snowpack in places that were previously covered.

Weather and CURRENT CONDITIONS
weather summary

High pressure is firmly parked over the forecast area. A weak air temperature inversion is in place with ridgetop remote sensors reporting air temperatures in the mid to upper 30s while mountain valley locations are generally in the 20s. Maximum daytime air temperatures are expected to reach the mid 40s to low 50s today for areas above 7,000'. Some high level cloud cover is expected to create partly cloudy skies for today. Ridgetop winds shifted from east to southwest yesterday evening and are light to moderate in speed. Wind speeds are forecast to become light as the day progresses. A dry cold front will pass through the region tomorrow afternoon/evening, decreasing air temperatures a few degrees at the upper elevations. Moderate speed west winds associated with frontal passage will help to mix out the air temperature inversion for the short term.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 34 to 40 deg. F.
Max. temperature in the last 24 hours: 48 to 52 deg. F.
Average wind direction during the last 24 hours: East shifting to Southwest
Average wind speed during the last 24 hours: 19 mph
Maximum wind gust in the last 24 hours: 29 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 7 to 13 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Partly cloudy skies. Partly cloudy skies, becoming mostly cloudy. Mostly cloudy skies, becoming partly cloudy.
Temperatures: 42 to 52 deg. F. 32 to 36 deg. F. 42 to 52 deg. F.
Wind Direction: West West West
Wind Speed: Light Light Light winds increasing to 10 to 15 mph with gusts to 25 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Partly cloudy skies. Partly cloudy skies, becoming mostly cloudy. Mostly cloudy skies, becoming partly cloudy.
Temperatures: 43 to 48 deg. F. 28 to 35 deg. F. 39 to 46 deg. F.
Wind Direction: West Southwest West
Wind Speed: 10 to 15 mph in the morning, becoming light. Light winds increasing to 10 to 15 mph after midnight. 15 to 25 mph with gusts to 35 mph.
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.