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.

A lingering low pressure moving through northern NV has kept the winds from decreasing and kept snow showers over the Sierra Crest. As this system moves eastward today, the winds should decrease and skies should start to clear, A small ridge of high pressure should build over the forecast area for this afternoon and evening. This high should cause slightly warmer daytime temperatures over the forecast area today. A second low follows this ridge. It should bring more clouds to the area tonight and a chance for snow showers through tomorrow.

Yesterday snow levels remained around 7000', and precipitation continued longer than expected. Between 3 and 4 inches of water fell along the Sierra Crest over the last 48 hours. Below 7000' most of this precipitation fell as rain. Above 7000' most of it fell as very dense, heavy snow. This combination of rain and heavy snow overloaded the already fragile snowpack and resulted in widespread avalanche activity. Several natural avalanches occurred in the Donner Summit area before daybreak yesterday on steep N-NE-E facing slopes between 7000'-8200'. These slides ranged in size but most were large enough to bury a person. Natural avalanches also occurred in the early morning hours in the Maggies Peak area near Emerald Bay and along the Sierra Crest north of Tahoe City. During the day yesterday, observers reported skier triggered avalanches on Maggies Peak. One person was carried 30-40' down-slope by a 12-18 inch deep, 15-20 ft wide slide on a steep, N-NW-facing rollover at 7000' on Maggies. He skied out of the slide safely. Several 36-38 degree N-NE facing test slopes released in the Mt Judah area as well. Caltrans reported 4 large avalanches on the Carson Spur resulting from early morning explosive control work.

The overnight drop in temperatures and less new precipitation today should allow the snowpack to begin to consolidate. However, wet, saturated snow should still exist below 7800' today in some areas. The warmer temperatures at these elevations should have kept the free water in the snowpack from freezing last night. These areas of wet snow will be the one avalanche concern today. Human-triggerable wet slabs could be possible on these slopes until the free water in the snowpack has time to refreeze.

Continued wind and more new snow during the day yesterday will cause the heavy wind slabs to remain as a second avalanche concern today. Failure of these slabs could result in avalanches large enough to bury a person. These wind slabs will be most prevalent on open, wind-loaded N-NE-E aspects. They will be largest near and above treeline where most of the precipitation fell as snow. Skiers, snowboarders, snow-mobilers, and cornice failures could all trigger avalanches involving these wind slabs. It may be possible that some of these wind slabs could still fail naturally; however, the best window for natural activity should have already passed.

Today's third avalanche concern will be the persistent layer of weak facets sitting between January's crusts and February's snow. In areas where this layer exists, the snowpack may not be able to handle the new loading that has occurred over the last 48 hours. Many slopes where this layer exists have already failed. On those that have not released, natural and human-triggered avalanche activity due to failure at this layer will remain possible on NW-N-NE aspects below 8700'. Avalanches involving this layer would be deep and destructive.

 

The bottom line:

Near and above treeline on slopes steeper than 35 degrees, the avalanche danger is MODERATE with pockets CONSIDERABLE on NW-N-NE-E aspects. Below treeline the avalanche danger on slopes steeper than 35 degrees remains CONSIDERABLE on NW-N-NE-E aspects, especially on slopes below 7800' in elevation. On the SE-S-SW-W aspects the avalanche danger is MODERATE at all elevations on slopes steeper than 35 degrees.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	27 deg. F.
Max. temperature in the last 24 hours:	32 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	58 mph
Maximum wind gust in the last 24 hours:	93 mph
New snowfall in the last 24 hours:	4 inches
Total snow depth:	124 inches

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

For 7000-8000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Partly cloudy with isolated snow showers on the west side of Lake Tahoe in the morning	Partly cloudy with a slight chance of snow showers after midnight	Mostly cloudy with a chance of snow
Temperatures:	33-42 deg. F.	22-27 deg. F.	29-36 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	15-25 mph with gusts to 40 mph decreasing to 10-20 mph in the afternoon	10-20 mph	10-20 mph with gusts to 30 mph
Expected snowfall:	O in.	O in.	up to 1 in.
For 8000-9000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Partly cloudy with isolated snow showers on the west side of Lake Tahoe in the morning	Partly cloudy with a slight chance of snow showers after midnight	Mostly cloudy with a chance of snow
Temperatures:	29-33 deg. F.	18-23 deg. F.	25-30 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	30-40 mph with gusts to 75 mph decreasing to 15-25 mph with gusts to 50 mph in the afternoon	25-35 mph with gusts to 45 mph	20-30 mph with gusts to 45 mph
Expected snowfall:	O in.	O in.	up to 1 in.