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.

Observations:

Even though we are not making observations, the observations page will still be updated as people submit observations. If you have snowpack or avalanche observations you would like to share with the community, please continue to send them in. Click here to submit avalanche observations, and click here to submit snowpack observations.

There are three major avalanche concerns for the remainder of this spring and into early summer:

Avalanche Concern #1 Wet Snow Instabilities:

The first is near surface loose wet snow avalanche activity. Usually this type of instability forms in response to daytime warming. You can use the Snotel and National Weather Service sites to monitor hourly temperatures at many points throughout the forecast area. Cloudy skies overnight and air temperatures above freezing do not allow the snowpack to refreeze well. When the snowpack does not refreeze overnight, other springtime activities that do not involve snow travel on steep slopes represent more prudent choices. Under clear skies, the top few inches of the snowpack will often refreeze despite near or slightly above freezing air temperatures. This light refreeze usually allows for a short period of good travel conditions during the early morning hours before surface wet snow instability becomes a concern. If a solid overnight refreeze occurs, getting out early can and finishing in time to have an early afternoon barbecue should be your goal. Start with east aspects and follow the sun to south, then to west, and finally to north aspects. Get off of your equipment on a regular basis and check boot penetration depth. Boot-top deep wet snow, significant roller ball activity, or any wet snow avalanche results from small test slopes all indicate that wet snow instabilities can occur. Moving to a different aspect with less sun exposure, terrain less than 25 degrees in slope angle without steeper terrain above it, or simply heading over to the beach for a picnic all represent great choices at this point. As a matter of etiquette, do not leave deep ruts in a slope that will freeze overnight and ruin the slope for others the next day.

Avalanche Concern #2 Deep Wet Slabs:

Deep wet slab avalanches represent the second spring avalanche concern. A deeply buried persistent weak layer still exists on some NW-N-NE aspects. In some areas melt water may percolate through the snowpack and destroy this layer, and in other areas the melt water may simply weaken this layer and cause it to break. Across the forecast area, the variability of this weak layer and the variability associated with how a snowpack melts and how that melt water moves through the snowpack makes predicting where and when and even if these kinds of avalanches will occur difficult at best. Due to this uncertainty and an insurmountable lack of information, naturally occurring deep wet slab avalanches cannot be ruled this spring. Slopes where free water has not yet percolated to this layer will hold the best potential for these avalanches. On the E-SE-S-SW-W aspects where a snowpack exists deep wet slabs could also become possible as the spring sun and warm air temperatures allow free water to percolate to the base of the snowpack. The time period when free water percolates into the deeper layers of the snowpack and drainage channels are not well established is when deep wet slab avalanches are most likely to occur. Areas where the snowpack rests on top of impermeable surfaces like granite slabs represent good places for these kind of slide to occur. However, they can occur anywhere that enough free water accumulates in the snowpack. These events are very difficult to predict and can result in large, destructive avalanches.

 Avalanche Concern #3 Storm Slabs and Wind slabs:

The third major concern involves avalanche activity that may occur during and after any late season storms. Expect a period of snowpack instability during the storm itself, then a second cycle of avalanche activity as rapid warming occurs post storm. During the storm, watch for typical signs of mid winter instability such as recent avalanche activity, wind loading, collapse, audible whumpfing sounds, and/or shooting cracks. Post storm, new snow will be very sensitive to rapid warming and direct sunlight. Pay close attention to layer bonding within the new snow and to the old snow surface beneath it. It can lose strength rapidly as the day progresses causing a significant increase in avalanche danger.

Other hazards such as cornice collapse, moats, glide cracks, and open creeks exist. Stay well back from abrupt edges along ridgelines as human triggered cornice collapse will remain possible during the spring. Stay out from under cornice areas that are not well frozen, especially if you can see water dripping from the cornice. Areas of weak snow around rocks, vegetation, and along the base of cliff bands exist. Move carefully around these features as the thin bridges of snow could collapse under body weight allowing you to fall into a melted hole next to the feature. Exercise caution when traveling near or attempting to cross creeks as wet snow along the banks can collapse under the weight of a person.

As the season begins to change, the morning air becomes crisp, and the days become shorter, check back on our home page for early season fundraising events for the 2012-2013 season. Enjoy your spring and summer and we will see you next fall.

The bottom line:

We have stopped issuing daily avalanche advisories until the fall of 2012. The avalanche danger can and will change quickly this spring. Continue to monitor changing conditions and use caution when traveling in the backcountry. For general spring avalanche information read the full spring avalanche statement.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	Check the SNOTEL and NWS remote sensor sites mentioned above. deg. F.
Max. temperature in the last 24 hours:	deg. F.
Average wind direction during the last 24 hours:
Average wind speed during the last 24 hours:	mph
Maximum wind gust in the last 24 hours:	mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	inches

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

For 7000-8000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Check in with the Reno NWS at the link above for the latest weather forecasts.
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.