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.


This Avalanche Advisory was published on March 19, 2010:


March 19, 2010 at 6:40 am

Early this morning, avalanche danger is LOW for all elevations and aspects. Pockets of MODERATE avalanche danger will develop at all elevations on E-SE-S-SW-W aspects 37 degrees and steeper in response to daytime warming.


Forecast Discussion:


High pressure is building over the forecast area. Sunny skies, above freezing air temperatures and decreasing winds are expected for today. Ridgetop winds remain moderate in speed out of the northeast this morning and are expected to shift to the north and become light to moderate in speed this afternoon. Remote sensors are reporting air temperatures above 8,000' in the upper 20s this morning.

Observations:

Observations made yesterday on Silver Peak (Pole Creek area) showed snow surface conditions that were a mix of melt freeze snow at all elevations on E-SE-S-SW-W aspects and cold snow not affected by melt freeze on N-NE aspects above 8,200'. This is very similar to snow surface conditions seen in other areas over the past few days (more info). Snowpit data collected at 7,900' on a large open ESE aspect 30 degree slope revealed a snowpack that was around 4 feet deep and showed evidence of past and present free water at all heights within the snowpack. Free water drainage from the snowpack appeared established at this location (pit profile, more info). Clear skies last night and below freezing air temperatures are expected to have allowed for a strong overnight refreeze of surface snow.

Avalanche concerns: Warming instability

Avalanche concerns for today continue to focus on wet snow instability. Expect areas of instability to form, especially by mid afternoon on E-SE-S-SW-W aspects at all elevations. Very isolated areas of wet snow instability are possible on NW-N-NE aspects below 7,500'. Any instability will most likely take the form of loose snow avalanches involving the top few inches of wet surface snow. Deep wet slab instability remains unlikely at this time.


The bottom line:

Early this morning, avalanche danger is LOW for all elevations and aspects. Pockets of MODERATE avalanche danger will develop at all elevations on E-SE-S-SW-W aspects 37 degrees and steeper in response to daytime warming.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: 26 to 30 deg. F.
Max. temperature in the last 24 hours: 41 to 43 deg. F.
Average wind direction during the last 24 hours: Northeast
Average wind speed during the last 24 hours: 35 mph
Maximum wind gust in the last 24 hours: 63 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 85 to 123 inches

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

For 7000-8000 ft:

  Friday: Friday Night: Saturday:
Weather: Sunny skies. Clear skies. Sunny skies.
Temperatures: 43 to 50 deg. F. 26 to 32 deg. F. 48 to 55 deg. F.
Wind direction: NE shifting to N Variable SW
Wind speed: 10 to 15 mph with gusts to 30 mph. Light winds Light winds increasing to 10 to 15 mph in the afternoon.
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Friday: Friday Night: Saturday:
Weather: Sunny skies. Clear skies. Sunny skies.
Temperatures: 42 to 48 deg. F. 26 to 32 deg. F. 44 to 51 deg. F.
Wind direction: NE shifting to N NW shifting to NE after midnight. SW
Wind speed: 15 to 25 mph with gusts to 65 mph in the morning. Winds decreasing to 10 to 15 mph with gusts to 35 mph in the afternoon. Up to 10 mph. Up to 10 mph in the morning. Winds increasing to 10 to 15 mph with gusts to 25 mph in the afternoon.
Expected snowfall: O in. O in. O in.

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