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.

The transition to a wet pattern for the region has occurred with cloud cover, increased southwest winds and light snow showers moving into the forecast area last night. New snow amounts this morning are around a trace with up to two inches of new snow expected today. Most of the snow shower activity for today is expected to occur after 11am. Remote sensors are reporting air temperatures in the low 20s to low 30s this morning for areas above 7,000'. Maximum daytime air temperatures are forecast to reach the mid 20s to upper 30s today for areas above 7,000'. Strong ridgetop winds will occur today and continue into tomorrow. Expect light snowfall today and tomorrow before a series of powerful storms impact the forecast area through this week and possibly into next.

Recent Observations:

When tracking a persistent weak layer, it is just that - persistent. Observations made yesterday on Andesite Ridge (Donner Summit area) fell right in line with other recent observations from around the forecast area. The persistent weak layer of crusts and faceted snow that exists in the middle to lower third of the snowpack on the vast majority of NW-N-NE aspects around the forecast area continues to show weakness and the ability to propagate collapse through the snowpack (pit profiles, videos, more info). Recent east winds have scoured snow off of the very top portion of N-NE aspect avalanche start zones, but a significant slab still sits on top of the well developed persistent weak layer on the mid and lower portion of wind scoured avalanche paths and other steep slopes. On E-SE-S-SW-W aspects, the snowpack is strong and stable. The persistent weak layer does not exist on these aspects due to sufficient melt freeze in late January and early February that kept the layer from forming. Snow surface conditions mid day yesterday had up to 3 inches of wet surface snow on southerly aspects and around 1 inch of wet snow in sun exposed areas on northerly aspects below 8,000'. No significant wet snow instability was observed. A snow surface refreeze is expected to have occurred last night in the vast majority of areas.

Today's Avalanche Concern: Persistent Deep Slabs

At this time, slab avalanches are difficult to trigger within the existing snowpack due in part to the strength of the overlying slab. That said, nearly all recent field data indicates that on NW-N-NE aspects the persistent weak layer of crust and facets just below the 1 to 5 foot slab of settled and cohesive mid February and early March storm snow has the necessary characteristics to propagate collapse. Add to that a trigger and a sufficiently steep slope, and a large deep slab avalanche will likely occur. Given the strength of the overlying slab, there will be a limited number of trigger points on any given slope that will allow force to penetrate through the slab and collapse the weak layer below. That suggests that a slope could be traveled by many individuals before the trigger point is loaded and an avalanche occurs. Exercise good travel habits and take a conservative approach as the consequences of becoming caught in a deep slab avalanche will be significant given the depth and density of the slab that will be involved. The current penetration depth of skis and snowmobiles will not touch or disrupt the weak layer, keeping even fully tracked out slopes suspect for future loading events such as the forecast storms this week. The minimal new snowfall amounts that accumulate today are not expected to cause any additional areas of snowpack instability.

The bottom line:

Pockets of MODERATE avalanche danger exist both above and below treeline on NW-N-NE aspects on slopes 35 degrees and steeper due to ongoing deep slab instability. The possibility of large destructive human triggered avalanches remains in these areas. For all other areas, avalanche danger is LOW.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	21-29 deg. F.
Max. temperature in the last 24 hours:	37-44 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	28 mph
Maximum wind gust in the last 24 hours:	59 mph
New snowfall in the last 24 hours:	trace to 0 inches
Total snow depth:	28-47 inches

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

For 7000-8000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Mostly cloudy skies with scattered snow showers.	Cloudy skies with isolated snow showers	Mostly cloudy skies with a slight chance of snow showers
Temperatures:	30 to 38 deg. F.	20 to 27 deg. F.	30 to 38 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	30 to 45 mph with gusts to 60 mph	25 to 35 mph with gusts to 50 mph	25 to 35 mph with gusts to 50 mph
Expected snowfall:	Up to 2 in.	0 to trace in.	0 to trace in.
For 8000-9000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Mostly cloudy skies with scattered snow showers.	Cloudy skies with isolated snow showers	Mostly cloudy skies with a slight chance of snow showers
Temperatures:	23 to 30 deg. F.	19 to 25 deg. F.	23 to 30 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	50 to 75 mph with gusts to 90 mph	45 to 60 mph with gusts 80 to 90 mph	50 to 60 mph with gusts to 80 mph
Expected snowfall:	Up to 2 in.	0 to trace in.	0 to trace in.