THIS AVALANCHE FORECAST EXPIRED ON March 22, 2018 @ 6:59 am
Avalanche Forecast published on March 21, 2018 @ 6:59 am
Issued by Steve Reynaud - Tahoe National Forest

CONSIDERABLE avalanche danger will exist today due to a combination of loose wet, deep slab, and wind slab avalanche problems.  A moderate to strong atmospheric river storm will bring widespread rain and high elevation snow throughout the forecast area over the next couple days.  Dangerous avalanche conditions will exist with natural and human triggered avalanches expected.

3. Considerable

?

Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

?

Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

?

Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Loose Wet
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Widespread rain today and tonight will make loose wet avalanches likely on all aspects and elevations.  Rain is forecasted up to 8000-8500' today and could fluctuate throughout the storm.  Many of the wet instabilities should be in the form of roller balls and pinwheels with larger loose wet avalanches capable of injuring and/or burying a backcountry user possible.

Avoid steep terrain that is being rained on.  Roller balls and pinwheels will be an indication that the surface snow is loosing strength and that larger loose wet avalanches could occur.

Avalanche Problem 2: Deep Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

A layer of graupel was deposited on top of a melt freeze crust before our last storm that has resulted in 4 deep slab avalanches-3 naturals and 1 remotely skier triggered avalanche on last Sunday.  This graupel/melt freeze crust combo is buried 3 to 5' deep and continues to show some reactivity and unstable snowpack test results.  This layer has been found in other areas within the forecast region but all known avalanche activity has been located in the Mt. Rose area.  All deep slab avalanches have been around 9000' and above and on East aspects.  As a large load impacts our area today and tomorrow, this layer could fail causing large and destructive avalanches.  These deep slabs will be possible on NE-E-SE aspects near and above 9000'.

The only effective deep slab 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. 

Avalanche Problem 3: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Gale force S/SW winds with high elevation snow will form wind slabs on NW-N-NE-E-SE aspects in near and above treeline terrain.  These wind slabs are expected to form above 8500' where snow is forecasted with no wind slabs expected below 8000' where mostly rain is forecasted.  Fluctuations in the snow level may increase or decrease this avalanche problem greatly depending on how much available snow there will be for wind transport.  Expected rain may also weaken recently built out cornices from the last storm causing them to fail downslope.

Look for blowing snow, cornice formation, and forming wind pillows.  Avoid steep wind loaded terrain and run out zones below cornices.

recent observations
Submit Observations

* A large whumpf was felt on Proletariat Bowl (Mt. Rose area) while investigating a recent deep slab avalanche.  This deep slab occurred over the weekend and had the same characteristics as the other deep slab avalanches that have occurred in the Mt. Rose area - layer of graupel on top of a melt freeze crust that was buried before our last storm.  Snowpack tests continued to show some unstable test results in this area.

* Wind transport was occurring at Twin Lakes ( Carson Pass area) with poor bonding of the old snow surface to the new wind transported snow.  Moderate blowing snow was also observed at Echo Summit area.

*  The graupel/melt freeze crust combo was observed on Hidden Peak (West Shore area) at 8880' on an E aspect.  Snowpack tests in this area showed no unstable test results. 

 

Weather and CURRENT CONDITIONS
weather summary

A winter storm warning is in effect from 5pm today through 5am Friday morning.  A moderate to strong atmospheric river has started to effect our forecast area.  Widespread heavy rain and high elevation snow is expected.  Ongoing precipitation is forecasted today with the heaviest rain/snow expected tonight through Thursday.  Snow levels should be in the 8000-8500' range for the majority of the storm but uncertainty exists.  Snow levels should drop down to 7000' by Thursday afternoon.  Little or no snow is expected down to lake level with this storm.  Gale force S and SW winds are forecasted throughout the majority of the storm.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 33 to 34 deg. F.
Max. temperature: 37 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 30 to 40 mph
Maximum ridgetop wind gust: 80 mph
New snowfall: .80 to 1.70'' rain to up to 4 inches
Total snow depth: 70 to 99 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy. Chance of snow. Rain likely through the day. Cloudy. Rain and snow. Cloudy. Rain and snow.
Temperatures: 40 to 45 deg. F. 32 to 37 deg. F. 34 to 39 deg. F.
Mid Slope Winds: SW S SW
Wind Speed: 15 to 25mph with gusts to 45mph. 15 to 30mph with gusts to 50mph. 15 to 25mph with gusts to 45mph.
Expected snowfall: .25 to .50 .60 to 1.10'' liquid | Possible 3 to 9 7 to 15
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy. Rain and snow likely. Cloudy. Snow and rain. Cloudy. Rain in the morning, snow through the day.
Temperatures: 36 to 41 deg. F. 29 to 35 deg. F. 31 to 36 deg. F.
Ridge Top Winds: SW SW S
Wind Speed: 30 to 45mph with gusts to 85mph. 35 to 55mph. Gusts to 90mph increasing to 100mph after midnight. 35 to 55mph with gusts to 115mph, shifting to the SW 45 to 60mph with gusts to 100mph in the afternoon.
Expected snowfall: 2 to 6 5 to 11 12 to 20
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.

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