THIS AVALANCHE ADVISORY EXPIRED ON February 28, 2015 @ 7:00 am
Avalanche Advisory published on February 27, 2015 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

The avalanche danger should remain LOW at all elevations and on all aspects today since only 1 inch of new snow is expected. As new snow and wind impact the forecast area tonight, the avalanche danger will rise quickly. A variety of avalanche problems including wind slabs, storm slabs, and some scattered persistent slabs could become possible by tomorrow. Continue to use normal caution when traveling in the backcountry.

1. Low

?

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

1. Low

?

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

1. Low

?

Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Loose Dry
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Cold new snow falling on top of smooth frozen snow surfaces means that loose snow sluffs will become possible today. These sluffs should remain very small and inconsequential since only 1 inch of new snow is expected. As more snow accumulates tonight and tomorrow, these sluffs may become larger and more widespread. By tomorrow morning storm slabs could replace the loose dry snow sluffs as a potential avalanche problem depending on the amount of new snow that falls tonight.

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

As new snow and wind begin to impact the forecast area today, new wind slabs will start to form on the leeward aspects in near and above treeline terrain. With only an inch of accumulation expected today, these wind slabs should remain very small and not pose a hazard to backcountry travelers unless much more snow than forecasted accumulates. As more snow accumulates tonight and tomorrow, the wind slabs will grow in size and become more widespread. Think of the tiny wind slabs and drifts that start to form today as a preview of where larger and more serious wind slabs will exist tomorrow.

Avalanche Problem 3: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

On some isolated near and below treeline NW-N-NE wind sheltered and shaded slopes above 8000 ft, a layer of weak sugary snow (near surface facets) up to 6 in. thick does exist at or near the snow surface. This soft weak layer of snow rests above a frozen rain crust that could serve as an efficient bed surface for snow to slide on. Today's 1 inch of new snow will not add enough of slab above this weak layer/bed surface combination to overload it, so persistent slabs should not represent a problem for backcountry travelers today. However, the 6-12 inches of new snow predicted tonight and tomorrow could form slabs above this weak layer/bed surface combination. Like the wind slabs mentioned above, watch where new snow accumulates on top of the existing weak layer today to help figure out where more serious persistent slabs may exist tomorrow.

recent observations

Hard frozen melt-freeze crusts dominated the snow surface on the northerly aspects on Waterhouse Peak yesterday. A few small isolated patches of soft weak surface snow 1-3 in. deep existed on some N aspects scattered among the frozen crusts. Similar to other northerly aspects around the region, some softer layers of weak snow did exist on top of a strong thick rain crust in the upper portion of the snowpack. This setup does represent a weak layer sitting on top of a bed surface that snow could slide on.

Weather and CURRENT CONDITIONS
weather summary

The winds shifted to the southwest, and cloud cover and wind speeds increased during the night as the cold low pressure system moved closer to the region. Some small snow showers also occurred during the night. Some remote sensors south of Highway 50 reported a trace of new snow. One sensor near Kirkwood even showed an inch of new snow. As the low pressure  moves into the area today, colder temperatures and gusty winds will represent its main effects. Expect daytime highs in the upper 20's to low 30's. Scattered snow showers could begin this morning, and the snow showers should become more widespread this afternoon. The forecast calls for about an inch of accumulation today with a slight chance for up to 3 inches by the end of the afternoon. The bulk of the snow should impact the region tonight and tomorrow morning. The forecast calls for 6-12 inches above 7000 ft. along the Sierra Crest and 3-7 inches at lake level. Since this snow should arrive as snow showers, accumulation amounts could vary greatly depending on location. West winds in the 30 to 35 mph range with gusts in the 50 to 55 mph range above 8000 ft. will continue into the night before they begin decreasing early tomorrow morning and during the day tomorrow. Temperatures should remain colder for the duration of this storm. Expect overnight lows in the teens tonight and daytime highs in the 20's tomorrow. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 24 to 31 deg. F.
Max. temperature in the last 24 hours: 38 to 46 deg. F.
Average wind direction during the last 24 hours: North shifting to west last night
Average wind speed during the last 24 hours: 15 to 25 mph
Maximum wind gust in the last 24 hours: 41 mph
New snowfall in the last 24 hours: trace to 0 inches
Total snow depth: 26 to 43 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy with scattered snow showers in the morning. Clouds and snow increasing during the day. Cloudy with snow showers Cloudy with snow showers and a slight chance of thunderstorms in the afternoon.
Temperatures: 30 to 37 deg. F. 16 to 23 deg. F. 23 to 30 deg. F.
Wind Direction: West West Variable
Wind Speed: 15 to 20 mph with gusts to 25 mph increasing to gusts to 35 mph in the afternoon 20 to 25 mph with gusts to 35 mph decreasing to 10 to 15 mph after midnight Light
Expected snowfall: up to 1 in. 2 to 5 in. 2 to 5 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy with scattered snow showers in the morning. Clouds and snow increasing during the day. Cloudy with snow showers Cloudy with snow showers and a slight chance of thunderstorms in the afternoon.
Temperatures: 29 to 35 deg. F. 17 to 23 deg. F. 22 to 28 deg. F.
Wind Direction: West West West
Wind Speed: 20 to 30 mph with gusts to 35 mph increasing to 50 mph in the afternoon 30 to 35 mph with gusts to 55 mph decreasing to 15 to 20 mph with gusts to 30 mph after midnight 10 to 15 mph in the morning decreasing in the afternoon
Expected snowfall: up to 1 in. 2 to 6 in. 2 to 6 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.