Avalanche Advisory published on March 3, 2015 @ 6:43 am
This advisory is valid for 24 hours
Issued by Brandon Schwartz - Tahoe National Forest
bottom line

Avalanche danger is LOW for all elevations and aspects. Please keep in mind that LOW danger does not mean no danger. Human triggered avalanches are unlikely but certainly not impossible today. Areas of wind slab and loose wet instability are expected in the backcountry today. Normal caution is advised.

How to read the advisory


Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human-triggered avalanches unlikely. Small avalanches in isolated areas or extreme terrain.

avalanche danger

How to read the advisory

1. Low

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Above Treeline

1. Low

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Near Treeline

1. Low

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Below Treeline

Avalanche danger is LOW for all elevations and aspects. Please keep in mind that LOW danger does not mean no danger. Human triggered avalanches are unlikely but certainly not impossible today. Areas of wind slab and loose wet instability are expected in the backcountry today. Normal caution is advised.

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human-triggered avalanches unlikely. Small avalanches in isolated areas or extreme terrain.
weather

Snow showers yesterday deposited another 1 to 5 inches of new snow in various locations around the forecast area. Accumulations were quick and sporadic for locations that received more that 2 inches. For today, expect decreasing cloud cover leading to sunny skies as high pressure begins to build over the forecast area. Ridgetop winds shifted from west to the north-northeast this morning during the pre-dawn hours. Northeast winds are expected to increase to moderate in speed as the day progresses with ridgetop gusts to 40 mph. Remote sensors are reporting air temperatures this morning in the upper teens to low 20s at 8,000' to 9,000' and minimal air temperature inversion conditions. Maximum daytime air temperatures are forecast to reach the low 20s to low 30s today for areas above 7,000'. For tomorrow expect sunny skies, decreasing winds, and the start of a warming trend.

recent observations

Observations made yesterday on Incline Lake Peak (Mount Rose area) indicated that settlement and bonding has occurred within the snowpack. Settlement cracks up to 2 inches wide were noted at the upper elevations. Recent new snow appeared well bonded to both itself and to either crust or old near surface facets that exist at the old snow/storm snow interface. Wind scouring and subsequent wind slab formation were noted along the summit ridge from recent NE winds. Wind slabs up to 1 foot thick were observed in lee areas. These slabs appeared well bonded with only minimal skier triggered cracking observed while traversing these slabs in low angle areas. These observations matched well with other recent observations from around the forecast area. Glossary of terms

Avalanche Problem 1:   Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    likely
    unlikely
  • Size ?
    large
    small
  • Trend ?
    Same Danger

Shifting ridgetop winds over the past few days have produced wind slabs 1 to 3 feet deep in lee areas. The strongest period of NE winds post storm event occurred Saturday night and was the contributor to the majority of development of the recently formed wind slabs. Increasing NE ridgetop winds today will transport the 1 to 5 inches of new snow that was deposited during snow showers yesterday. Forecast wind speed for today is expected to transport only the few inches of new snow from yesterday keeping any additional wind slab development small. One caveat: If actual wind speeds today exceed forecast amounts, there is plenty of snow available for wind transport near and above treeline which could lead to larger than expected and more unstable than expected wind slab development. Glossary of terms

Avalanche Problem 2:   Loose Wet
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    likely
    unlikely
  • Size ?
    large
    small
  • Trend ?
    Increasing Danger

With clearing skies in the forecast for today, the stronger levels of March solar radiation will affect the snowpack. Significant amounts of snow is expected to begin falling off of rocks and trees, leading to roller ball activity. Human triggered pin wheels are expected in sun expose areas as minute amounts of free water form at the snow surface. The vast majority of loose wet instability is expected to occur below 8,000' as roller balls and pin wheels, with more limited amounts at higher elevations. Actual loose wet avalanches are an unlikely but not impossible event today in sun exposed areas at any elevation on slopes 37 degrees and steeper.

advisory discussion

What about Persistent Slabs?

Snowpit data collected over the past few days has yet to reveal areas where persistent slab instability has formed. The necessary set of slab and weak layer characteristics have not been observed all in the same place at the same time. Areas where the buried near surface facet weak layer is most well developed are also the areas that received the least amount of storm snow and have a minimal new snow load. In areas of greater amounts of storm snow and significant new snow load, the new overlying slab has been slow to become highly cohesive. This has allowed time for the old near surface facets to increase the degree of rounding and subsequent strength under the insolation of the storm snow layer. Field observations will continue to monitor this layer interface where it exists above 8,000' on NW-N-NE aspects in near treeline and below treeline terrain. For now, persistent slabs are removed from the list of avalanche problems until such a time that field observations indicate problematic development. Glossary of terms

CURRENT CONDITIONS  Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 19 to 23 deg. F.
Max. temperature in the last 24 hours: 26 to 31 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 14 mph
Maximum wind gust in the last 24 hours: 26 mph
New snowfall in the last 24 hours: 1 to 5 inches
Total snow depth: 40 to 52 inches
Two-Day Mountain Weather Forecast  Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
  Today Tonight Wednesday
Weather: Partly cloudy to sunny skies. Clear skies. Sunny skies.
Temperatures: 27 to 34 deg. F. 17 to 22 deg. F. 34 to 41 deg. F.
Wind direction: NE NE Variable
Wind speed: 5 to 10 mph 10 to 15 mph in the evening, becoming light. Light winds
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
  Today Tonight Wednesday
Weather: Partly cloudy to sunny skies. Clear skies. Sunny skies.
Temperatures: 23 to 30 deg. F. 15 to 21 deg. F. 31 to 38 deg. F.
Wind direction: North to northeast NE to E E to SE
Wind speed: 10 to 20 mph in the morning, increasing to 15 to 25 mph with gusts to 40 mph. 15 to 25 mph with gusts to 35 mph in the evening, decreasing to 10 to 20 mph. 10 to 20 mph with gusts to 30 mph, decreasing to 10 to 20 mph in the afternoon.
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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