Avalanche Advisory published on December 18, 2014 @ 6:52 am
This advisory is valid for 24 hours
Issued by Andy Anderson - Tahoe National Forest
bottom line

Human-triggered wind slab avalanches remain possible today in certain areas. Pockets of MODERATE avalanche danger exist on wind-loaded NW-N-NE-E-SE aspects 35 degrees and steeper in near and above treeline terrain. Convex rollovers, areas near rocks, unsupported slopes, couloirs/gullies, and other complex terrain represent the most likely places to find lingering wind slabs.

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

?

Above Treeline

2. Moderate

?

Near Treeline

1. Low

?

Below Treeline

Human-triggered wind slab avalanches remain possible today in certain areas. Pockets of MODERATE avalanche danger exist on wind-loaded NW-N-NE-E-SE aspects 35 degrees and steeper in near and above treeline terrain. Convex rollovers, areas near rocks, unsupported slopes, couloirs/gullies, and other complex terrain represent the most likely places to find lingering wind slabs.

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.
weather

Another 1 to 3 inches of snow accumulated in the last 24 hours. Some light snow showers could continue this morning with up to 2 inches of new snow possible along the Sierra Crest. These showers should give way to calmer weather this afternoon and tonight as a small high pressure ridge builds over the area. The forecast calls for another storm to move into the  region on Friday and Saturday bringing more snow (up to 3 inches tomorrow) and increased southwest winds.

recent observations

Yesterday observations on Castle Peak still revealed instabilities associated with wind slabs on wind-loaded slopes. Skier and small cornice piece triggered shooting cracks occurred on wind-loaded N-NE-E aspects in near and above treeline terrain. One test slope also slid with a 14 to 16 inch slab. The wind slabs in this area rested on top of a mix of old crusts and a layer of softer snow at the base of the wind slab. Across I-80 on Wildflower Ridge (Mt. Judah) large cornice pieces did not trigger cracking or slab failures in the slopes below. Snowpit data from near Billy's Peak in the Deep Creek drainage showed increasing stability. Observations from Tamarack Peak and the east ridge of Relay Peak in the Mt. Rose area also did not reveal signs of instability.

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

Wind slabs should grow more difficult to trigger today, however human-triggered wind slabs will remain possible in certain areas. Convex rollovers, areas near rocks, unsupported slopes, couloirs/gullies, and other complex or extreme terrain on wind-loaded NW-N-NE-E-SE aspects represent the best places to trigger wind slabs, and the places they take longest to stabilize. These wind slabs measure 1 to 2 ft. in depth, and avalanches resulting from their failure could involve enough snow to bury a person especially in the most heavily wind-loaded areas or in areas where terrain traps magnify the consequences of the wind slabs. A mix of old crusts and soft snow layers at the base of the wind slabs can serve as the weak layer. If a person does trigger a wind slab in one of the places where they remain sensitive, these slabs can break above the person who triggers them.

CURRENT CONDITIONS  Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 22 to 28 deg. F.
Max. temperature in the last 24 hours: 25 to 31 deg. F.
Average wind direction during the last 24 hours: Southwest to South
Average wind speed during the last 24 hours: 20 mph
Maximum wind gust in the last 24 hours: 37 mph
New snowfall in the last 24 hours: 1 to 3 inches
Total snow depth: 25 to 39 inches
Two-Day Mountain Weather Forecast  Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
  Today Tonight Friday
Weather: Mostly cloudy with isolated snow showers in the morning Mostly cloudy Cloudy with a chance of snow
Temperatures: 30 to 37 deg. F. 25 to 30 deg. F. 32 to 36 deg. F.
Wind direction: Southwest Southwest Southwest
Wind speed: Light in the morning increasing to 10 to 15 mph in the afternoon 15 to 20 mph with gusts to 30 mph 15 to 25 mph with gusts to 40 mph
Expected snowfall: up to 1 in. 0 in. up to 3 in.
For 8000 ft. to 9000 ft.
  Today Tonight Friday
Weather: Mostly cloudy with isolated snow showers in the morning Mostly cloudy Cloudy with a chance of snow
Temperatures: 28 to 32 deg. F. 22 to 28 deg. F. 26 to 32 deg. F.
Wind direction: Southwest Southwest Southwest
Wind speed: 10 to 15 mph with gusts to 25 mph 15 to 25 mph with gusts to 40 mph 25 to 35 mph with gusts to 45 mph increasing to 55 mph in the afternoon
Expected snowfall: up to 1 in. 0 in. up to 3 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.

Subscribe to Central Sierra Avalanche Advisory | Avalanche Forecast From the Sierra Avalanche Center