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.


This Avalanche Advisory was published on November 16, 2012:


November 16, 2012 at 7:45 am

Rain on snow is expected to create areas of MODERATE avalanche danger both above and below treeline on NW-N-NE aspects on slopes 35 degrees and steeper. For all other areas, avalanche danger remains LOW.


Forecast Discussion:


The first of several waves associated with this storm cycle is moving into the forecast area this morning. Rain and snow will begin to fall across the forecast are today with light showers in the morning becoming more widespread as the day progresses. Snow levels are expected to rise to around 7,000' today. Precipitation amounts of 0.25 inches of rain are expected below 7,000' and 2 to 3 inches of new snow are expected at 8,000 and above'. Ridgetop winds remain out of the southwest this morning and are light in speed. Winds are expected to increase to moderate in speed as the day progresses. Air temperatures at or slightly above freezing this morning will warm well into the 30s today at most elevations. Snow levels are forecast to rise to 7,500'+ tonight and Saturday.

Observations:

Recent observations from around the forecast area have revealed the existing snowpack in good condition to handle new snow loading with one exception. Areas of well developed faceted snow have been noted in the Carson range on northerly aspects above 9,000'. New snow loading over the next several days may allow this layer to become an active weak layer allowing for snowpack failure below the old/new snow interface. Other areas of minor near surface faceting have been observed along the Sierra Crest between 6,500' and 8,000' on shaded northerly aspects. These areas are expected to handle new snow loading fairly well, but are expected to be more sensitive to wet snow instability from rain on snow. For more details on recent observations, click here.

Avalanche concerns:

Rain on snow is expected to cause some amount of wet snow instability today where faceted snow exists on NW-N-NE aspects below 7,000'-7,500'. Areas of both human triggered and naturally occurring wet loose snow avalanches and roller balls will be possible today. Any avalanches that occur are likely to be small and not involve enough snow to bury a person unless a terrain trap is involved. Minimal new snow amounts at the upper elevations will not create any significant new slabs today, keeping the areas of highest hazard at the mid and lower elevations.


The bottom line:

Rain on snow is expected to create areas of MODERATE avalanche danger both above and below treeline on NW-N-NE aspects on slopes 35 degrees and steeper. For all other areas, avalanche danger remains LOW.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest


Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:

0600 temperature: 30 to 33 deg. F.
Max. temperature in the last 24 hours: 44 to 48 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 17 mph
Maximum wind gust in the last 24 hours: 40 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 6 to 30 inches

Two-Day Mountain Weather Forecast - Produced in partnership with the Reno NWS

For 7000-8000 ft:

  Friday: Friday Night: Saturday:
Weather: Cloudy skies with rain and snow. Snow level around 7,000'. Cloudy skies with rain and snow. Snow level at 7,500' or higher. Cloudy skies with rain and snow. Snow level at 7,500' or higher.
Temperatures: 38 to 41 deg. F. 28 to 34 deg. F. 35 to 39 deg. F.
Wind direction: SW SW SW
Wind speed: 10 to 15 mph with gusts to 25 mph. 20 to 25 mph with gusts to 40 mph. 30 to 35 mph with gusts to 50 mph.
Expected snowfall: 0 to 2 in. 2 to 4 in. 2 to 4 in.

For 8000-9000 ft:

  Friday: Friday Night: Saturday:
Weather: Cloudy skies with snow. Cloudy skies with snow. Some rain possible. Cloudy skies with snow.
Temperatures: 30 to 38 deg. F. 36 to 40 deg. F. 30 to 38 deg. F.
Wind direction: SW SW SW
Wind speed: 20 to 25 mph with gusts to 40 mph. 15 to 25 mph with gusts to 35 mph. 25 to 30 mph with gusts to 40 mph.
Expected snowfall: 2 to 3 in. 2 to 4 in. 3 to 5 in.