THIS AVALANCHE FORECAST EXPIRED ON March 29, 2020 @ 7:00 am
Avalanche Forecast published on March 28, 2020 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

People triggered slab avalanches 1 to 3 ft deep that broke on a weak layer of buried surface hoar yesterday. This persistent slab problem exists at all elevations. Unstable slabs of wind drifted snow may also break on this weak layer. People can still trigger persistent slab and wind slab avalanches today and they can still trigger them remotely from lower angle terrain. Choosing conservative terrain can help avoid getting caught by this unusual problem. MODERATE avalanche danger will continue.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Persistent Slab
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Persistent slab avalanches remain a problem. These avalanches fail on a weak layer of surface hoar that formed prior to the recent storm. In sheltered areas, people have triggered avalanches about 1 ft deep. In more exposed areas where slabs of wind drifted snow exist above this layer, the avalanches have measured 2 to 3 feet in depth. Yesterday people triggered several of these avalanches. The avalanches propagated long distances across slopes and wrapped around terrain features. In some cases, people triggered them from a distance while traveling in lower angle terrain connected to steeper slopes. People recreating on slopes where this weak layer exists will still be able to trigger persistent slab avalanches today. This kind of avalanche problem is unusual for this area and it will take time to go away.

Open areas on NW-N-NE aspects at all elevations represent the most likely places to find this persistent slab problem. Avalanches could fail mid-slope or at the top of a slope. They could break above or behind the person who triggers them with very wide propagation or be remotely triggered. Manage your aspects and slope angles carefully and be careful with terrain to connected to steeper slopes. 

 

Avalanche Problem 2: Wind Slab
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Unstable slabs of wind drifted snow also still linger on wind-loaded and cross-loaded NW-N-NE-E-SE aspects. In areas where these wind slabs exist on top of the buried surface hoar or a graupel layer, they will behave as the persistent slabs mentioned above. Human triggered wind slab avalanches remain possible today.

Look for built out cornices, wind pillows, and steep wind loaded terrain where unstable wind slabs are most likely to exist. Wind slab avalanches have been propagating wider than normal. Avoid areas below large cornices and wind loaded slopes.

Plenty of great snow exists on lower angle more sheltered terrain. Choosing these areas will help find excellent recreation conditions and avoid potential wind slab or persistent slab avalanches.

 

recent observations
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Several human triggered avalanches occurred yesterday. Observers reported avalanches in below, near, and above treeline terrain on Donner Peak, Mt. Judah, near Silver Peak, and on Anderson Ridge. These all propagated farther than expected across the slope. One was triggered from a lower angle slope adjacent to the avalanche. While no one was injured there were several close calls.

Observers also reported unstable test results on Silver Peak and Echo Peak on buried surface hoar.  Some minor cracking occurred on a wind-loaded slope on Chickadee Ridge and on a sunny warm slope near Echo Summit. 

Warming snow was reported on southerly aspects near Little Truckee Summit and in Johnson Canyon. 

Weather and CURRENT CONDITIONS
weather summary

A weak storm system should bring cloud cover to the area today. By this afternoon some light snow showers could begin. Snow showers should continue through the night before tapering off tomorrow. The forecast calls for limited amounts of snow with this storm with up to 6 inches accumulating by Sunday afternoon. This storm also looks like it comes with some light SW wind, but wind speeds should remain well below those normally associated with a Sierra 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: 14 to 24 deg. F.
Max. temperature: 22 to 32 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 15 to 25 mph
Maximum ridgetop wind gust: 58 mph
New snowfall: 0 inches
Total snow depth: 63 to 85 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy. Chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 35%. Cloudy. Snow likely. Snow levels below 7000 feet. Chance of precipitation is 60%. Cloudy. Snow showers likely. Snow levels below 7000 feet. Chance of precipitation is 70%.
Temperatures: 33 to 38 deg. F. 20 to 25 deg. F. 33 to 38 deg. F.
Mid Slope Winds: Light winds. Light winds. Light winds becoming southwest around 15 mph with gusts to 25 mph in the afternoon.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. 90% probability of 1 to 3 inches. 10% probability of 3 to 5 inches. | SWE = up to 0.15 inch. 90% probability up to 2 inches. 10% probability of 2 to 3 inches. | SWE = up to 0.15 inch.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy. Chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 35%. Cloudy. Snow likely. Snow levels below 7000 feet. Chance of precipitation is 60%. Cloudy. Snow showers likely. Snow levels below 7000 feet. Chance of precipitation is 70%.
Temperatures: 28 to 34 deg. F. 17 to 22 deg. F. 28 to 34 deg. F.
Ridge Top Winds: Light winds. Southwest around 15 mph. Gusts up to 25 mph after midnight. Southwest around 15 mph with gusts to 30 mph.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. 80% probability up to 3 inches. 20% probability of 3 to 5 inches. | SWE = up to 0.15 inch. 80% probability of 1 to 3 inches. 20% probability of 3 to 4 inches. | SWE = up to 0.15 inch.
Disclaimer

This avalanche forecast is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This forecast 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 forecast applies only to backcountry areas outside established ski area boundaries. This forecast describes general avalanche conditions and local variations always occur. This forecast expires 24 hours after the posted time unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the avalanche forecast call (530) 587-3558 x258