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 1, 2009:


April 1, 2009 at 6:59 am

This morning, avalanche danger is LOW for all elevations and aspects. Pockets of MODERATE danger may develop below treeline on sun-exposed, SE-S-SW-W aspects, 37 degrees and steeper in response to daytime warming.


Forecast Discussion:


The forecast calls for clearing skies today as the low-pressure system east of the forecast area moves toward the central U.S. The winds should shift back to the north and increase today. Daytime highs should remain a few degrees cooler than yesterday. Another low-pressure system should start to impact the forecast area tomorrow and could bring some snow for Thursday night and Friday. The winds should start to shift to the west and increase ahead of this storm tomorrow morning.

Yesterday, observations between Carson Pass and Red Lake Peak and on Signal Mountain (west of Donner Summit along I-80) both showed firm, refrozen snow surfaces on the E-SE-S-SW-W aspects at all elevations until about 10 am. By 11:00 am the top 2-3 inches of frozen surface snow had melted and provided great corn conditions on the E-SE-S aspects. The SW-W aspects softened to the same degree about 30 minutes to 1 hour later. On Red Lake Peak, 4-5 inches of soft, wet melt/freeze snow existed on the sun-exposed SE-S-SW aspects by 1pm. The afternoon cloud cover shielded the snow from the sun and prevented much more softening which kept widespread wet-snow instabilities from forming. On the northerly aspects a mix of wind-affected snow and breakable crusts existed on top of cold, unconsolidated snow in most areas.

The warm air temperatures and intense March sun should melt and soften the snow surface again today. This melting will form free water in the snowpack. This water will dissolve some of  the bonds holding the snow together making the snowpack weaker until the bonds can refreeze tonight. Less melting should occur today due to cooler daytime high temperatures, a northerly wind, and a strong overnight refreeze. The prolonged melt/freeze cycle and winter rain events have also established drainage channels through the snowpack that should keep the melt water from completely saturating a single layer. The combination of less melting and these drainage channels should prevent large, widespread wet-snow instabilities from forming today. If temperatures rise more than forecasted or the clouds dissipate faster than forecasted enough melting could occur for some wet-snow instabilities to form on steep sun-exposed SE-S-SW-W aspects. If you find yourself sinking into wet snow up to the top of your boots or start seeing/triggering pinwheels and roller-balls, move to a safer location on either a more northerly aspect or low angle terrain.


The bottom line:

This morning, avalanche danger is LOW for all elevations and aspects. Pockets of MODERATE danger may develop below treeline on sun-exposed, SE-S-SW-W aspects, 37 degrees and steeper in response to daytime warming.


Andy Anderson - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: 26-30 deg. F.
Max. temperature in the last 24 hours: 43 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 18 mph
Maximum wind gust in the last 24 hours: 43 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 140 inches

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

For 7000-8000 ft:

  Wednesday: Wednesday Night: Thursday:
Weather: Partly cloudy this morning becoming mostly sunny this afternoon Mostly clear Mostly sunny in the morning becoming partly cloudy with a chance of snow showers in the afternoon
Temperatures: 41-48 deg. F. 28-34 deg. F. 37-44 deg. F.
Wind direction: Northwest shifting to the north North Southwest
Wind speed: 10-20 mph with gusts to 30 mph 10 mph with gusts to 25 mph 15-20 mph with gusts to 30 mph increasing to 20-30 mph with gusts to 55 mph in the afternoon
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Wednesday: Wednesday Night: Thursday:
Weather: Partly cloudy this morning becoming mostly sunny this afternoon Mostly clear Mostly sunny in the morning becoming partly cloudy with a chance of snow showers in the afternoon
Temperatures: 34-41 deg. F. 26-32 deg. F. 32-37 deg. F.
Wind direction: Northwest shifting to the north North shifting to the west West and southwest
Wind speed: 15-25 mph increasing to 20-35 mph with gusts to 65 mph 20-25 mph with gusts to 45 mph decreasing to 10-20 mph after midnight 20-35 mph with gusts to 50 mph increasing to 30-40 mph with gusts to 75 mph in the afternoon
Expected snowfall: O in. O in. O in.