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 March 17, 2009:

March 17, 2009 at 6:55 am

Near and above treeline, pockets of MODERATE avalanche danger exist on N-NE aspects, 37 degrees and steeper. At all elevations on E-SE-S-SW-W aspects, avalanche danger will become MODERATE with pockets of CONSIDERABLE danger forming on E-SE aspects 37 degrees and steeper in response to daytime warming.

Forecast Discussion:

The warm weather system that brought rain and snow to the forecast area over the past 48 hours has cleared out overnight. Sunny skies and warm daytime air temperatures are expected today. Storm totals are running 4 to 7 inches over the northern half of the forecast area. Significantly less precipitation occurred south of Hwy 50. Air temperatures in the upper 20s to mid 30s this morning are forecast to climb into the 40s to low 50s today. Ridgetop winds remain out of the southwest this morning, but have decreased to moderate in speed.

Yesterday, observations made on Jake's Peak (West Shore Lake Tahoe) indicated rain up to around 7,500' with a stable layer of wet surface snow ranging from 6 to 12 inches deep in areas below 8,000'. Above 8,000', new snow amounts ranging from 4 to 6 inches with fairly poor bonding at the old/new snow interface was observed. Spillover and subsequent snowfall accumulation yesterday in the northeastern portion of the forecast area exceeded expectations. On Tamarack Peak (Mount Rose area), rain was observed up to 8,000' with around 6 inches of new snow at 9,500'. Some minor skier triggered cracking was observed within the new snow in wind loaded areas. Stability tests performed at 9,500' on a N aspect, 34 degree slope revealed poor bonding and very easy shears at the old/new snow interface. Further stability tests indicated that fracture propagation was unlikely on this weak layer. A report of a natural point release wet snow avalanche was received from outside the boundary of the Bear Valley Ski Area. The avalanche occurred at 7,800' on an E aspect, 34 degree slope and is believed to have started as roller balls. The point release avalanche measured around 100 feet wide at the debris after running 1,000' vertical feet and eventually entraining the top one foot of the snowpack.

Two avalanche concerns exist for today. The first concern is wet snow instability. Significant amounts of wet snow exist on all aspects below 8,000' due to the recent rain and warm air temperatures. Little to no refreeze of the surface snow occurred last night. Daytime warming will fuel further instability within the wet snow today, especially in sun exposed areas. E-SE aspects are particularly suspect today due to the mix of recent wind loaded snow and rain from yesterday combined with significant solar radiation today. Natural and human triggered avalanches will be possible on these aspects today at all elevations. Human triggered wet snow avalanche will also be possible on most other aspects today, especially below 7,500'. Moderate speed SW ridgetop winds may cause enough convective cooling to keep snow surface melting at the ridgetops to a minimum. In more wind sheltered areas just below the ridges, significant surface melting will occur in these same areas.

The second concern is lingering pockets of recently wind loaded snow above 8,000' in near and above treeline areas. Stiff but fairly shallow slabs that may be difficult to trigger are expected on steep N-NE aspects. These slabs will involve only the recent storm snow and should be limited to within the top 1 foot of the snowpack.


The bottom line:

Near and above treeline, pockets of MODERATE avalanche danger exist on N-NE aspects, 37 degrees and steeper. At all elevations on E-SE-S-SW-W aspects, avalanche danger will become MODERATE with pockets of CONSIDERABLE danger forming on E-SE aspects 37 degrees and steeper in response to daytime warming.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature: 26 to 28 deg. F.
Max. temperature in the last 24 hours: 31 to 32 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 55 mph
Maximum wind gust in the last 24 hours: 84 mph
New snowfall in the last 24 hours: Trace to 4 inches
Total snow depth: 148 inches

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

For 7000-8000 ft:
  Tuesday: Tuesday Night: Wednesday:
Weather: Partly cloudy skies. Partly cloudy skies. Partly cloudy skies.
Temperatures: 47 to 53 deg. F. 27 to 35 deg. F. 49 to 55 deg. F.
Wind direction: SW SW Variable
Wind speed: 10 to 20 mph with gusts to 35 mph in the afternoon. 10 to 15 mph with gusts to 30 mph in the evening. Light winds.
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:
  Tuesday: Tuesday Night: Wednesday:
Weather: Partly cloudy skies. Partly cloudy skies. Partly cloudy skies.
Temperatures: 40 to 48 deg. F. 23 to 30 deg. F. 43 to 49 deg. F.
Wind direction: SW SW SW shifting to SE in the afternoon.
Wind speed: 20 to 30 mph with gusts to 55 mph. Gusts decreasing to 40 mph in the afternoon. 10 to 20 mph with gusts to 35 mph in the evening. Up to 10 mph.
Expected snowfall: O in. O in. O in.