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.

Increasing cloud cover and increasing southwest winds are forecast for today ahead of an approaching weather system. Rain and snow is expected to begin tonight with snow level starting around 7,200' and lowering to 5,800' to 6,500' on Wednesday. New snow accumulations of 3 to 6 inches are expected above 7,000' by late Wednesday. Little to no new snow accumulation is expected below 6,500'. This morning, remote sensors above 8,000' are reporting air temperatures 23 to 30 deg F. Low and mid elevation areas are forecast to warm significantly more today than upper elevation areas. Maximum daytime air temperatures for 7,000' to 8,000' are forecast at 46 to 52 deg F. while areas above 8,000' are forecast to reach 38 to 44 deg F. Ridgetop winds are moderate in speed out of the southwest this morning and are forecast to becoming strong to gale force in speed tonight and continue through tomorrow.

Recent Observations:

Observations made yesterday on Mt. Tallac (Desolation Wilderness area) revealed that previous persistent instability associated with near crust facets had undergone significant rounding and improved stability over the past week. Where snowpit data was gathered on a NE aspect at 9,000', melt water from the recent warm air temperatures had not reached the depth of the old near crust facet layer as has been observed on other NW-N-NE aspects below 8,000'. The rounding of old facets and improved stability matched well with other observations made around the forecast area over the past week (videos, pit profiles, more info).

Little to no wet snow formed yesterday on N-NE aspects between 6,400' and 9,100' on Mt. Tallac. Full shade areas remained frozen while sun exposed areas held less than 1 inch of wet surface snow at 1pm. Greater amounts of wet snow were observed on E-SE-S aspects yesterday with 1 to 3 inches of wet surface snow on top of supportable melt-freeze crust at 1pm between 7,800' and 9,100'. Below 7,800' the snowpack was in a full height isothermal melt state with no frozen phase melt-freeze crust present at 1pm. Snowpack depth between 6,400' and 7,800' on E-SE-S aspects ranged from 6 inches to 3 feet. Despite the full height wet snow with no frozen crust, the low elevation snowpack remained supportable to skier weight at 1pm.

Avalanche Problem #1: Loose Wet Avalanches

Even with cloud cover last night, below freezing air temperatures are expected to have allowed for a decent snow surface refreeze for areas above 6,500'-6,800'. Areas below this elevation are not expected to have experienced a very strong refreeze due to above freezing air temperatures and cloud cover limiting radiational cooling. The depth and strength of snow surface refreeze last night will be greatest at higher elevations. Areas of wet snow instability are possible this afternoon below 8,000' on E-SE-S-SW-W aspects as snow surface melting occurs in response to daytime warming.

Tracking Persistent Slabs

Snowpit data collected this past week indicates that significant rounding and strength gains have occurred in the near crust facet layers that contributed to three human triggered avalanches on March 9 and 10. Below 8,000', melt water percolating through the snowpack has changed the once sugary faceted snow of the old weak layers into rounded well bonded snow crystals. In areas above 8000 ft, free water has not reached the old near crust facet layers, but significant rounding and strength gains have occurred in those areas as well. Over the past several days, snowpit tests targeting these old weak layers have indicated that propagation in response to weak layer collapse has become unlikely (videos, pit profiles, more info). The existing snowpack is expected to have sufficient strength to handle new snow loading tonight and tomorrow. Persistent deep slab avalanche activity is unlikely to occur this week.

The bottom line:

This morning, avalanche danger is LOW for all elevations and aspects. Pockets of MODERATE avalanche danger may form this afternoon on the E-SE-S-SW-W aspects below 8,000' on slopes 35 degrees and steeper due to daytime warming. Human triggered wet snow avalanches may become possible.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	25 to 30 deg. F.
Max. temperature in the last 24 hours:	39 to 47 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:	41 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	50 to 82 inches

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

For 7000-8000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Mostly cloudy skies.	Cloudy skies with snow showers developing after 9pm. Snow level 6,500' to 7,200'.	Cloudy skies, becoming mostly cloudy. Snow likely. Snow level 5,800' to 6,500'.
Temperatures:	46 to 52 deg. F.	24 to 31 deg. F.	39 to 47 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	10 to 15 mph with gusts to 25 mph, increasing to 20 to 25 mph with gusts to 35 mph in the afternoon.	25 to 30 mph with gusts to 40 mph. Gusts increasing to 55 mph after midnight.	35 to 45 mph with gusts to 65 mph.
Expected snowfall:	O in.	Up to 3 in.	Up to 3 in.
For 8000-9000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Mostly cloudy skies.	Cloudy skies with snow showers developing after 9pm.	Cloudy skies, becoming mostly cloudy. Snow likely.
Temperatures:	38 to 44 deg. F.	20 to 27 deg. F.	29 to 36 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	20 to 25 mph with gusts to 35 mph. Gusts increasing to 45 mph in the afternoon.	35 to 40 mph with gusts to 60 mph, increasing to 50 to 55 mph with gusts to 80 mph after midnight.	50 to 60 mph with gusts to 90 mph.
Expected snowfall:	O in.	Up to 3 in.	Up to 3 in.