Avalanche Advisory published on March 20, 2018 @ 6:58 am
This advisory is valid for 24 hours
Issued by Steve Reynaud - Tahoe National Forest
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How to read the advisory

MODERATE avalanche danger will continue today due to loose wet and deep slab avalanche problems.  Loose wet avalanche activity will be possible at all elevations as rapid warming occurs and rain becomes possible this afternoon.  Deep slab avalanches remain possible in isolated areas of the forecast region.  Avalanche danger is expected to increase over the next few days as a larger storm impacts our area.

  • 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.

Light rain with high elevation snow is expected late afternoon and into tonight.  Clouds will be on the increase today with snow levels starting around 6000' and increasing to 7500' by this afternoon.  Limited moisture is expected today, .10''.  Tonight snow levels will continue to rise up to 8000' with .20'' to .45'' of available moisture with 2 to 5'' of snow expected above 8000'. 

A moderate to strong atmospheric river is scheduled for our area starting Wednesday and going through Thursday night.  Snow levels will be starting in the 7500-8500' range and should lower by Thursday afternoon.  2 to 3' of snow is forecasted above 7500' with 6 to 12'' expected down to 7000'.    

recent observations

* A deep slab avalanche with a crown height estimated at 4 feet was remotely skier triggered Sunday on Mt. Houghton on an E to ENE aspect at approx 10,200'. The party triggered a large collapse just below the ridgetop. Investigation down slope revealed the avalanche crown below a cliff band.

* A crown line profile was done on a recent deep slab avalanche SE of Relay Peak.  The weak layer was a layer of graupel on top of the melt freeze crust that is below the recent storm snow.  This graupel/melt freeze combo seems to only exist above 9000' on aspects that had melt freeze crusts pre storm.  This layer is thought to be responsible for all 3 of the recent deep slab avalanches in the Mt. Rose area.  Snowpack tests done at the crown line showed unstable results showing propagation is still likely.

* Observations from The Nipple (Carson Pass area) showed a mostly stable snowpack.  Tests and observations focused on the old melt freeze crusts did not show any signs of instabilities.

* Other observations around the forecast region, Jobs Peak and Shirley Canyon, show some instabilities continue to exist.


Avalanche Problem #1: Loose Wet

Loose wet avalanche activity is expected to increase today with rapid warming and rising snow levels.  Wet instabilities will be possible on all aspects and elevations today.  Rain is expected up to 7500' by this afternoon and up to 8000' by this evening.  Most loose wet instabilities should be in the form of roller balls or pinwheels but some larger loose wet avalanches are possible and could be large enough to injure or bury a backcountry user-size D2.

Monitor the weather and snow surface conditions in your area today.  Thick, wet surface snow may occur with rapid warming and/or rain on snow later today.  Look for roller balls and other signs that the snow surface is loosing strength.  Avoid travel on steep slopes where roller balls are occurring.

Avalanche Problem #2: Deep Slab

2 natural and 1 human triggered deep slab avalanches have been reported in the Mt. Rose area post storm.  On Sunday, the most recent, a group of backcountry users remotely triggered a deep slab avalanche in the Mt. Houghton area.  After further investigation, a layer of graupel that fell on Tuesday before our last big storm is sitting on top of a melt freeze crust and below the recent storm snow.  This graupel/melt freeze crust combo is now buried 3 to 5' deep.  All 3 of these deep slab avalanches have been on East aspects, above 9000', and in the Mt. Rose area.  Snowpack tests done yesterday at the crown of a recent deep slab avalanche still show that this layer is reactive and that propagation continues to be likely.

Many unknowns still exist about this deep slab issue.  The only effective management strategy is avoidance-staying off aspects of concern, using slopes under 30 degrees on aspects of concern and avoiding connected terrain where remote triggering could occur.  Any avalanches associated with this weak layer would be large and have severe consequences. 

CURRENT CONDITIONS  Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 27 to 31 deg. F.
Max. temperature in the last 24 hours: 40 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 15 to 35 mph
Maximum wind gust in the last 24 hours: 52 mph
New snowfall in the last 24 hours: inches
Total snow depth: 69 to 100 inches
Two-Day Mountain Weather Forecast  Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
  Today Tonight Wednesday
Weather: Mostly cloudy. Slight chance of snow in the afternoon. Cloudy. Rain and snow likely. Cloudy. Rain and snow likely in the morning then rain and snow in the afternoon.
Temperatures: 40 to 46 deg. F. 32 to 37 deg. F. 38 to 43 deg. F.
Wind direction: SW SW SW
Wind speed: 10 to 15mph in the morning becoming light. Gusts up to 35mph. 10 to 15mph with gusts to 30mph increasing to 20 to 30mph with gusts to 50mph after midnight. 20 to 30mph with gusts to 50mph.
Expected snowfall: Up to 1 in. 2 to 5 in. 1 to 3 in.
For 8000 ft. to 9000 ft.
  Today Tonight Wednesday
Weather: Mostly cloudy. Chance of snow in the afternoon. Cloudy. Snow and rain likely. Cloudy. Snow and rain likely in the morning then snow and rain in the afternoon.
Temperatures: 36 to 42 deg. F. 30 to 36 deg. F. 34 to 39 deg. F.
Wind direction: SW SW SW
Wind speed: 20 to 30mph. Gusts to 60mph decreasing to 50mph in the afternoon. 25 to 40mph with gusts to 70mph increasing to 35 to 55mph with gusts to 95mph after midnight. 30 to 50mph with gusts to 85mph.
Expected snowfall: Up to 1 in. 2 to 5 in. 1 to 5 in.

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.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258