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 13, 2007:


April 13, 2007 at 0:00 am

Forecast Discussion:


This advisory was posted on Friday, April 13th, 2007 at 6:58 am

The bottom line: Near and above treeline, avalanche danger is MODERATE on recently cross loaded and sun exposed SE aspects, 35 degrees and steeper where new snow sits on an old snow bed surface. Below treeline the avalanche danger is LOW.

A fast moving high pressure system will pass through the forecast area today. Ridgetop winds over the past 24 hours have shifted from northwesterly to northerly to northeasterly to easterly. Ridgetop winds are expected to decrease to light and shift clockwise from easterly to southwesterly today. Air temperatures today will warm with an expected increase in maximum daytime air temperature of 10 to 15 degrees over yesterday. A splitting weather system is expected to bring snow to forecast area on Saturday. Ridgetop winds are expected to increase to strong overnight ahead of the approaching weather system.

Yesterday morning, shifting ridgetop winds created areas of unstable snow on cross loaded ESE aspects near and above treeline. Two small (R1,D1) soft slab avalanches were intentionally skier triggered on the Proletariat slope on Tamarack Peak in the Mount Rose area. Both avalanches occurred at 9860' on cross loaded, 115 degree true(ESE) aspect start zones ranging from 39-44 degrees in slope angle. The soft slabs initially fractured 1 foot deep at the interface of the new snow deposited Wednesday morning and the second event of new snow deposited Wednesday night. Slab thickness decreased to 4 inches when measured 10 feet down slope of the crown. Both avalanches ran about 50' in linear distance on the slope.

With ridgetop winds continuing to shift to easterly overnight, significant redistribution of recently wind transported snow is expected. Most areas of instability that existed yesterday on ESE aspects will be removed by E wind scouring of the recently deposited snow. Cross loaded SE gullies remain the most likely location for any snowpack instability today. Today's daytime warming and solar radiation will increase instability on cross loaded SE gullies in areas where new snow sits on top of an old snow bed surface. In many areas, new snow has been transported onto bare ground on SE-S-SW-W aspects. No significant snowpack instability is expected in these areas due to the presence of excellent anchoring.

Human triggered avalanches are possible today in any sun exposed areas where recently wind transported snow has been deposited onto an old snow surface. Cross loaded SE aspect gullies are the most likely area for this snowpack instability to occur. Natural avalanche activity is unlikely but not impossible today on SE aspects. Naturally occurring snowpack instability is expected to be limited to roller ball activity on all sun exposed slopes, as snow melts off of rocks and trees.

The bottom line: Near and above treeline, avalanche danger is MODERATE on recently cross loaded and sun exposed SE aspects, 35 degrees and steeper where new snow sits on an old snow bed surface. Below treeline the avalanche danger is LOW.

We will raffle a BCA backpack, beacon, shovel, and probe package on April 17th as a way to say thanks to everyone who has sent us a donation in the mail or via Pay Pal this season. All individuals who have donated $10 or more to SAC are automatically entered in this raffle. Thanks to all of our sponsors, the ski days, and everyone who has donated funding this winter, we have met our operating budget for this season and have a start on next year's funding. For more details about our financial situation please click here.

Brandon Schwartz, Avalanche Forecaster

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Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 21 deg. F
Max. temperature at Sierra Crest past 24 hours: 32 deg. F
Average wind direction at Sierra Crest past 24 hours: Northerly shifting to easterly
Average wind speed at Sierra Crest past 24 hours: 30 mph
Maximum wind gust at Sierra Crest past 24 hours: 55 mph
New snow fall at 8,200 feet past 24 hours: 0 inches
Total snow depth at 8,200 feet: 59 inches

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Mountain Weather Forecast For Today:
Sunny skies.
Temperature forecast for 8,000 to 9,000 feet: 40 - 46 degrees F.
Ridgetop winds forecast for the Sierra Crest: Easterly 10 - 15 mph, shifting to southwesterly as the day progresses.
Snowfall expected in the next 24 hours: 0 inches

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2 Day Mountain Weather Forecast:
7000 to 8000 Feet:
Today, sunny skies with daytime highs around 49 degrees F. East winds at 10 to 15 mph, shifting to the southwest in the afternoon. Tonight, partly cloudy with overnight lows around 30 degrees F. Southwest winds at 20 to 30 mph. Saturday, cloudy skies with a chance of snow showers in the morning. Snow likely in the afternoon with a slight chance of thunderstorms. Snow accumulation up to 5 inches. Daytime highs 37 to 43 degrees F. Southwest winds at 25 to 35 mph with gusts to 50 mph are expected.

Above 8000 Feet:
Today, sunny skies with daytime highs 40 to 46 degrees F. East winds at 10 to 15 mph, shifting to the southwest in the afternoon. Tonight, partly cloudy with overnight lows around 30 degrees F. Southwest winds at 20 to 35 mph with gusts to 80 mph after midnight. Saturday, cloudy skies with a chance of snow showers in the morning. Snow likely in the afternoon with a slight chance of thunderstorms. Snow accumulation up to 6 inches. Daytime highs 31 to 39 degrees F. Southwest winds at 30 to 45 mph with gusts to 90 mph, decreasing to 60 mph in the afternoon are expected.


The bottom line:


Andy Anderson - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: deg. F.
Max. temperature in the last 24 hours: deg. F.
Average wind direction during the last 24 hours:
Average wind speed during the last 24 hours: mph
Maximum wind gust in the last 24 hours: mph
New snowfall in the last 24 hours: O inches
Total snow depth: inches

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

For 7000-8000 ft:

  Friday: Friday Night: Saturday:
Weather:
Temperatures: deg. F. deg. F. deg. F.
Wind direction:
Wind speed:
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Friday: Friday Night: Saturday:
Weather:
Temperatures: deg. F. deg. F. deg. F.
Wind direction:
Wind speed:
Expected snowfall: O in. O in. O in.