Avalanche Advisory published on February 9, 2016 @ 6:58 am
This advisory is valid for 24 hours
Issued by Steve Reynaud - Tahoe National Forest
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Early this morning, low avalanche danger exists on all aspects and elevations.  As daytime warming begins, pockets of moderate avalanche danger will form on E-SE-S-SW aspects at all elevations due to loose wet avalanche problems.  Avalanche danger will remain low on W-NW-N-NE aspects at all elevations.

 

How to read the advisory


Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches unlikely; human-triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas.

avalanche danger

How to read the advisory

2. Moderate

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Above Treeline

2. Moderate

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Near Treeline

2. Moderate

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Below Treeline

Early this morning, low avalanche danger exists on all aspects and elevations.  As daytime warming begins, pockets of moderate avalanche danger will form on E-SE-S-SW aspects at all elevations due to loose wet avalanche problems.  Avalanche danger will remain low on W-NW-N-NE aspects at all elevations.

 

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches unlikely; human-triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas.
Avalanche Problem 1: Loose Wet
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    likely
    unlikely
  • Size ?
    large
    small
  • Trend ?
    Same

Air temperatures at 6am above 7000' were well above freezing and ranged from the mid 30's to low 40's.  Winds have shifted direction from the E to the S-SW and should be light to moderate in speed today above 7000'.  Radiational cooling under clear skies has helped to marginally refreeze the snow surface on these solar aspects.  Although any refreeze that has occurred should be thin and short lived as daytime warming occurs.

The snowpack on E-SE-S-SW aspects is made up of 3-4'' of wet surface snow with colder, dryer, snow below that, on top of  rain crust.  The thin surface refreeze should go away and start to loose supportability within the morning hours.  Human triggered wet loose avalanches will become possible on slopes steeper than 35 degrees.  Most of these loose wet avalanches will be in the form of human triggered pin wheels or roller balls but in some cases could be large enough loose wet avalanches to injure or bury a backcountry user.  In isolated cases, these loose wet avalanches have entrained the dry snow below the wet surface snow and have slid on the buried rain crust and caused much larger and destructive avalanches.

Timing will be important if you plan to travel on solar aspects today.  Avoid steep solar aspects when daytime warming occurs.  Current roller balls or pin wheels will be an indication that the snow surface has lost supportability and strength.  Hand pits and boot penetration may help give clues to upper snowpack strength.  

recent observations

Recent observations over the last several days show similar snowpack characteristics throughout the forecast region.  Warm overnight temperatures have created weak melt freeze conditions on most E-SE-S-SW aspects at all elevations.  Loose wet instabilities have formed by mid morning on these aspects due to daytime warming and a weak overnight refreeze.  Most instabilities have been in the form of human triggered pin wheels or roller balls, although some larger loose wet avalanches have occurred.

On Mt. Lola (Independence Lake area) wet snow existed by 9:15am on east aspects.  Above 8000', east winds have scoured most exposed N-NE-E aspects and helped to limit any wet snow instabilities.  On solar aspects, test pits found several inches of wet surface snow on top of colder, dryer snow on top of rain crust.  Snowmobile cuts on test slopes failed to produce any loose wet instabilities. 

CURRENT CONDITIONS  Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 37 to 43 deg. F.
Max. temperature in the last 24 hours: 46 deg. F.
Average wind direction during the last 24 hours: NE shifting to S
Average wind speed during the last 24 hours: 20 to 25 mph
Maximum wind gust in the last 24 hours: 58 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 66 to 81 inches
weather

A strong high pressure ridge over the west will continue through this week.  Well above average temperatures are forecasted to be 10 to 15 degrees warmer than average for today.  Valley inversions are in place with mid and upper elevations in the mid 30' to low 40's this morning.  Winds have shifted direction to the S/SW and should generally be in the light to moderate range.

Two-Day Mountain Weather Forecast  Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
  Today Tonight Wednesday
Weather: Sunny Clear Sunny then becoming partly cloudy.
Temperatures: 45 to 52 deg. F. 26 to 34 deg. F. 45 to 52 deg. F.
Wind direction: S SW SW
Wind speed: 10 to 15mph 10 to 15mph with gusts to 25mph after midnight. 10 to 15mph with gusts to 25mph in the morning.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
  Today Tonight Wednesday
Weather: Sunny. Clear. Sunny then becoming partly cloudy.
Temperatures: 43 to 50 deg. F. 24 to 31 deg. F. 43 to 50 deg. F.
Wind direction: SW SW SW
Wind speed: 15 to 20mph with gusts to 30mph. 10 to 15mph with gusts to 25mph increasing to 20 to 25mph with gusts to 40mph after midnight. 15 to 25mph with gusts to 35mph.
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer

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.

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