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.

Moisture left over from the small wave of low pressure that contributed to yesterday's thunderstorms also allowed cloud cover to linger over the mountains last night and this morning. This thin cloud cover should persist today. By this afternoon more isolated thunderstorms could develop over the region. Temperatures have started to cool off some with this morning's lows about 5-10 degrees cooler than the last two days. Daytime highs still remain well above normal today in the upper 50's and low 60's above 7000 ft today. Increased cloud cover and the cooling trend should continue as a low pressure slowly moves into the region on Wednesday and Thursday. Overnight lows tonight and daytime highs tomorrow should drop another 5-10 degrees.

Recent Observations:

On Mt. Tallac yesterday, Sunday's overnight refreeze had already melted on all aspects by 9am. 4-8 inches of wet unconsolidated snow existed at all elevations on the NE aspects by 10 am and deeper wet snow existed on the warmer aspects. Similar conditions had formed on Incline Lake Peak up to 9500 ft. by noon (photo). In both of these areas, several human-triggered and natural wet loose avalanches had occurred on a wide variety of aspects over the last few days. Ski cuts on test slopes in these two areas yesterday also triggered more wet loose snow sluffs. On Tallac these sluffs would occur on slopes down to 30 degrees in steepness. Snowpit data on a NE aspect on the south side of Tallac showed a spring-like snowpack with melt-freeze snow all the way to the ground. The old persistent weak layer had also metamorphosed into melt-freeze snow in this snowpit (more info). On Incline Lake Peak, melt freeze snow only existed in the upper 2-3 ft of the snowpack (more info).

Warm air temperatures combined with some cloud cover overnight and this morning will have prevented much if any refreezing from occurring. Another warm day with periods of sunshine will quickly cause enough melting for the already wet snowpack to lose strength. As the snowpack weakens, wet snow instability will form quickly today on all aspects and at all elevations. Roller balls, wet loose snow avalanches, and wet slab avalanches all remain possible.

Like previous days, human-triggered wet snow instabilities should represent most of today's avalanche activity; however, natural avalanches will remain possible in isolated areas. Due to uncertainty surrounding the precise timing of wet snow avalanches and the difficulty associated with predicting these instabilities, conservative decision making remains a prudent choice under these conditions. Surface instabilities such as roller balls and pinwheels or simple observations such as stepping off of one's skis, snowboard, or snowmobile and sinking up to boot-top depth or more in wet snow can indicate potential instability on a slope.

Other things to think about: The Persistent Weak Layer

The depth of the persistent weak layer and the strength of the snow above it have made triggering a deep slab avalanche on NW-N-NE aspects unlikely. At this time data indicates collapsing this layer would require an extremely large trigger or significant weakening of the snowpack. Spring melting could eventually cause enough snowpack weakening for a deep wet slab avalanche cycle to occur. Even though data indicates conditions that could create this scenario have not yet arrived, they keep getting closer as more and more melting occurs each day and free water percolates deeper into the snowpack.

The bottom line:

Widespread MODERATE avalanche danger will form quickly today on all aspects at all elevations on slopes 30 degrees and steeper in response to daytime warming. Pockets of CONSIDERABLE danger may form this afternoon on slopes 35 degrees and steeper. The majority of instability that occurs today is likely to be human triggered, but natural avalanches are possible in isolated areas.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	37-43 deg. F.
Max. temperature in the last 24 hours:	55-62 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	25 mph
Maximum wind gust in the last 24 hours:	61 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	22-74 inches

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

For 7000-8000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Mostly cloudy with isolated thunderstorms in the afternoon	Mostly cloudy	Mostly cloudy with a slight chance of showers in the morning and scattered thunderstorms in the afternoon
Temperatures:	54-60 deg. F.	35-41 deg. F.	45-53 deg. F.
Wind direction:	South to southwest	Southwest	Southwest
Wind speed:	10-20 mph with gusts to 30 mph in the afternoon	10-20 mph with gusts to 35 mph	15-25 mph with gusts to 40 mph
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Mostly cloudy with isolated thunderstorms in the afternoon	Mostly cloudy	Mostly cloudy with a slight chance of showers in the morning and scattered thunderstorms in the afternoon
Temperatures:	48-54 deg. F.	33-40 deg. F.	41-47 deg. F.
Wind direction:	South	Southwest	Southwest
Wind speed:	15-25 mph with gusts to 40 mph	20-35 mph with gusts to 60 mph	25-40 mph with gusts between 50 and 70 mph
Expected snowfall:	O in.	O in.	O in.