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.

Yesterday's cold front brought five to eight inches of low density snow to the area since midnight on Tuesday. The snow showers ended yesterday afternoon as the front moved south and east out of the area. By mid morning yesterday, the winds had shifted to the northeast and increased. Those strong east and northeast winds should continue today as a high pressure ridge begins to replace yesterday's cold front. Air temperatures should remain colder than normal with daytime highs in the upper 20's and low 30's in the mountains today. As this high pressure becomes more established, the winds should decrease and the temperatures should rise. By tomorrow winds speeds should drop into the 10-15 mph range and daytime highs should climb into the 40's. This high pressure should also keep skies clear and sunny for the next few days.

Recent Observations:

The persistent weak layer comprised of old crusts and weak sugary snow (facets) still exists near the base of the snow that fell at the end of February and the beginning of March. Observations across the forecast area have shown that this problematic layer has become more variable as it tries to adjust to the weight of the slab on top it. Yesterday, snowpit data and observations from Tamarack Peak (more info, snowpit, video), Deep Creek (more info, photo, videos), and Flagpole Peak (more info) all showed some degree of variability. On Flagpole skiers reported easy compression test failures on this layer in one area and more stable results just 200 ft away. On Tamarack Peak (PST video) and in Deep Creek (ECT and PST Videos), tests in some areas showed that larger triggers may be needed to break this layer, but once it does break fractures could still travel through the weak layer. Tests on other slopes in these areas yielded more stable results. Ski cuts on steep northerly test slopes on Tamarack Peak where this weak layer exists did not result in failures. On Tamarack Peak the NE winds did scour the N-NE aspects and deposit some small shallow wind slabs up to six inches deep on the W-SW aspects. Some skier-triggered shooting cracks up to 2 ft in length did occur on these small features.

Today's Primary Avalanche Concern: Persistent Deep Slabs

As the persistent weak layer continues to adjust to weight of the snow above it, triggering avalanches on this layer should become more difficult. However, due to the way that these kind of layers stabilize, areas of stability and areas of instability could exist within a few feet of each other on the same slope. In areas where this layer exists, where it remains weak, and where the right trigger gets applied to the slope in the right spot, large human-triggered deep slab avalanches remain possible today. Pockets of terrain both above and below treeline on NW-N-NE aspects represent the most likely areas where this layer both exists and remains weak. Areas near exposed rock outcrops and cliffs, steep unsupported slopes, and slopes with trigger points are locations where triggering a deep slab avalanche would be easier. Caution and conservative decision making remain prudent due to the variability of this layer and the consequences of its failure. Digging into the snowpack will reveal whether or not this layer exists. The difference between the snow in this layer and the snow above it remains very easy to see and feel.

Today's Secondary Avalanche Concern: Warming Instabilities

With the strong spring sunshine expected today and new snow on the sun-exposed aspects due to wind-loading from the NE winds, some warming instabilities may form on sun-exposed SE-S-SW aspects today. These should remain limited to small and inconsequential surface instabilities like roller balls and pinwheels due to the continued NE winds and cooler temperatures. However, some larger warming instabilities may be possible on the steep wind-loaded SE aspects. In some isolated areas on these slopes small human-triggered slab avalanches may become possible due to daytime warming and sun exposure. If temperatures climb higher than forecasted, these kinds of instabilities could become more widespread.

The bottom line:

Pockets of MODERATE avalanche danger exist on NW-N-NE-E-SE aspects on slopes 35 degrees and steeper both above and below treeline due to ongoing deep slab instability and some sun-exposure. Even though they seem to be growing less likely,  large destructive human-triggered avalanches remain possible today in some areas.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	0-7 deg. F.
Max. temperature in the last 24 hours:	16-21 deg. F.
Average wind direction during the last 24 hours:	Northeast
Average wind speed during the last 24 hours:	35-40 mph
Maximum wind gust in the last 24 hours:	86 mph
New snowfall in the last 24 hours:	4-5 inches
Total snow depth:	33-53 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Sunny	Clear	Sunny
Temperatures:	27-33 deg. F.	16-22 deg. F.	37-44 deg. F.
Wind direction:	Northeast	East	East
Wind speed:	30-40 mph with gusts to 55 mph decreasing to 20-30 mph with gusts to 45 mph in the afternoon	25-30 mph with gusts to 40 mph decreasing to 15-20 mph with gusts to 30 mph after midnight	10-15 mph decreasing in the afternoon
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Sunny	Clear	Sunny
Temperatures:	25-32 deg. F.	16-23 deg. F.	36-43 deg. F.
Wind direction:	Northeast	Northeast shifting to the east after midnight	Southeast
Wind speed:	40-50 mph with gusts to 65 mph decreasing to 30-40 mph with gusts to 55 mph in the afternoon	30-35 mph with gusts to 45 mph decreasing to 20-25 mph with gusts to 35 mph after midnight	10-15 mph with gusts to 25 mph decreasing in the afternoon
Expected snowfall:	O in.	O in.	O in.