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 April 19, 2009:


April 19, 2009 at 6:46 am

This morning the avalanche danger is LOW. Areas of MODERATE avalanche danger should quickly develop due to daytime warming on E-SE-S-SW-W aspects 37 degrees and steeper at all elevations today.


Forecast Discussion:


After another night of above freezing temperatures, daytime highs should climb into the mid to upper 50's above 7000' today. By tomorrow the forecast area could see record high temperatures. This high pressure should remain over the forecast area into at least the middle of the week. The forecast calls for light north and east winds through tomorrow.

On Mount Judah by 10:30 am yesterday, 2-3 inches of wet corn snow existed on the surface of the sun-exposed E-SE-S aspects up to 8200'. The SW-W aspects quickly followed suit, and by 11:00 am similar conditions existed on these aspects. Some small human-triggered roller balls occurred on a 39 degree, SE facing test-slope at 7900' at 12:00 pm. A mix of supportable and breakable crusts, wind scoured surfaces, and a few patches of heavy, unconsolidated snow existed on the NW-N-NE aspects above 7500'. Below 7500' melt-freeze conditions existed on any slope that receives sunshine.

Today's main avalanche concern will be wet-snow instabilities. After an overnight refreeze due to radiational cooling, the snow surface should melt and soften quickly today due to warm daytime temperatures and the intense April sun. This melting will produce free water in to the snowpack which will weaken the snowpack by dissolving the bonds between the snow grains. Enough warming and melting could occur for human-triggered, wet-snow instabilities like roller balls, pinwheels, and small point-release avalanches to be possible today. The most likely areas for these instabilities will be on steep, sun-exposed, E-SE-S-SW-W aspects. Well established drainage channels that prevent free water from saturating any one layer in the snowpack should keep wet-slab avalanches unlikely. However, they  are not impossible especially in areas where the snowpack sits on an impermeable ground surface like a granite slab. Plan to be off of any sun exposed slopes before they get too soft and wet. To help determine when a slope has become unsafe, use observations of surface wet-snow instabilities and simple tests like stepping into the snow (if you sink into wet snow above your ankles it is a good time to move to a different slope).


The bottom line:

This morning the avalanche danger is LOW. Areas of MODERATE avalanche danger should quickly develop due to daytime warming on E-SE-S-SW-W aspects 37 degrees and steeper at all elevations today.


Andy Anderson - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: 38-40 deg. F.
Max. temperature in the last 24 hours: 51-55 deg. F.
Average wind direction during the last 24 hours: Northeast
Average wind speed during the last 24 hours: 15 mph
Maximum wind gust in the last 24 hours: 36 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 132 inches

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

For 7000-8000 ft:

  Sunday: Sunday Night: Monday:
Weather: Sunny Clear Sunny
Temperatures: 54-61 deg. F. 33-41 deg. F. 58-65 deg. F.
Wind direction: Northeast Variable Northeast
Wind speed: up to 10 mph Light up to 10 mph
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Sunday: Sunday Night: Monday:
Weather: Sunny Clear Sunny
Temperatures: 52-58 deg. F. 35-41 deg. F. 56-62 deg. F.
Wind direction: Northeast Variable East
Wind speed: 10 mph with gusts to 25 mph in the morning Light 10 mph
Expected snowfall: O in. O in. O in.