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 April 15, 2010:


April 15, 2010 at 6:49 am

MODERATE avalanche danger will form on E-SE-S-SW-W aspects at all elevations on slopes 35 degrees and steeper due to daytime warming.


Forecast Discussion:


A high pressure over the forecast area today will bring warmer temperatures, clearer skies, and a light southerly wind to the area. Today's daytime highs should reach 10 degrees higher than yesterday's and push up into the upper 40's even above 8000'. Another weak disturbance due to the low pressure north and west of the area should pass through the region tomorrow afternoon. Increased southwest winds, some cloud cover, and slightly cooler temperatures will be the main effects of this disturbance.

Observations:

Shallow, cold, soft snow remained on the north aspects of Incline Lake Peak above 8600' yesterday. On the more sun-exposed E-SE-S aspects, 1-3 inches of soft, wet snow existed on top of a firm and supportable melt-freeze crust. Since much less snow fell in this area during the last storm, the recent snow on these aspects is much closer to becoming good corn snow than the snow along the crest. Hand pits and ski cuts on test slopes showed good bonding between the recent snow and the snow below it on all aspects in this area yesterday. A few small roller balls did occur near SE-S facing cliffs; however, these did not entrain enough snow to pose much of a threat to backcountry travelers. Overnight lows in the 20's and clear skies should have allowed the snowpack to undergo a solid overnight refreeze.

Avalanche Concern #1: Warming Instabilities

Wet-snow instabilities that form due to daytime warming will again comprise the primary avalanche concern today. The intense April sunshine, lack of significant cloud cover, and daytime highs in the 40's and even low 50's will all work to make these instabilities more widespread today. The E-SE-S-SW-W aspects will hold the best potential for these types of instabilities. However, wet-snow instabilities could form on any slopes that receive significant sunshine including some of the more northerly aspects. Most of these warming instabilities should take the form of point-release avalanches and other surface instabilities; however, some wet-slab avalanches may be possible in isolated areas as well.


The bottom line:

MODERATE avalanche danger will form on E-SE-S-SW-W aspects at all elevations on slopes 35 degrees and steeper due to daytime warming.


Andy Anderson - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: 23-28 deg. F.
Max. temperature in the last 24 hours: 29-39 deg. F.
Average wind direction during the last 24 hours: South southwest
Average wind speed during the last 24 hours: 35 mph
Maximum wind gust in the last 24 hours: 78 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 106-155 inches

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

For 7000-8000 ft:

  Thursday: Thursday Night: Friday:
Weather: Partly cloudy Partly cloudy becoming mostly cloudy after midnight Mostly cloudy with a slight chance of showers
Temperatures: 45-52 deg. F. 25-35 deg. F. 42-49 deg. F.
Wind direction: South Southwest Southwest
Wind speed: 10 mph 10 mph 10-15 mph
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Thursday: Thursday Night: Friday:
Weather: Partly cloudy Partly cloudy becoming mostly cloudy after midnight Mostly cloudy with a slight chance of snow showers
Temperatures: 38-48 deg. F. 30-38 deg. F. 34-43 deg. F.
Wind direction: South South South shifting to the southwest
Wind speed: 10-15 mph with gusts to 25 mph 10-15 mph 10 mph increasing to 15-25 mph with gusts to 35 mph
Expected snowfall: O in. O in. O in.

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