THIS ADVISORY EXPIRED ON January 9, 2021 @ 6:58 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche CenterhT_h
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How to read the advisory

In most areas, triggering an avalanche is becoming more difficult. Some exceptions include areas with a shallow snowpack where old weak snow remains closer to the surface or places where new snow and wind may form small slabs of drifted snow today especially in the northern part of the forecast area. In these places, human-triggered avalanches may remain possible. The avalanche danger remains MODERATE at all elevations. 


  • 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.
recent observations

* Observers reported more unstable test results on the Dec 11 facet layer in areas where the snowpack remains shallow. Unstable test results came in from Elephant's Hump (Carson Pass) and on Signal Peak (lower elevation peak west of Donner Summit). 

* On Silver Peak and on Castle Peak in areas with a deeper snowpack few signs of instability were reported. Snowpit data from Silver Peak indicated that the Dec 11 facets continue to slowly gain strength.  

* Observers reported variable conditions yesterday with some soft surface snow on sheltered upper elevation slopes around Elephant's Hump, Castle Peak, and Silver Peak. In more exposed areas wind-scoured, wind-packed, and rain crusted surfaces existed.  At lower elevations, a sometimes breakable sometimes supportable rain crust existed on most slopes.

Avalanche Problem #1: Wind Slab

Strong SW winds last night and today may form some small slabs of drifted snow on leeward aspects (NW-N-NE-E-SE) near ridgelines. In many areas, not much snow exists for transport so these wind slabs should remain small. In the areas north of I80, more widespread wind slabs may form if new snow accumulates today. Even in these areas, the wind slabs should remain relatively small since only up to 2 inches of new snow is forecast. 

Look for blowing snow, new cornice development, and wind pillows as clues to where wind slabs may exist. Even though they may remain small, wind slab avalanches could still have consequences, especially in complex or extreme terrain. 

Avalanche Problem #2: Persistent Slab

Old weak snow still remains buried in the snowpack. Fortunately, data targeting the persistent weak layer (Dec 11 facets) indicates a strengthening trend, and triggering a persistent slab is growing more difficult in most places. Unfortunately, persistent weak layers are notoriously variable and do not gain strength uniformly. Some areas where the snowpack remains shallow still exhibit signs of instability like whumpfs, shooting cracks, and unstable snowpit tests. Specific areas with reports of a shallow unstable snowpack include the Carson Pass and Ebbetts Pass areas as well as lower elevation areas in other parts of the forecast region. Triggering a persistent slab avalanche may remain possible on a steep slope where the weak layer sits closer to the surface. A person hitting just the right spot (trigger point) on a slope or larger triggers like multiple people on a slope may still be problematic.  

Even though the likelihood of triggering one of these avalanches has decreased, the consequences of being caught in one have not. This uncertain, high-consequence, low-probability problem still warrants caution. Terrain less steep than 30 degrees not connected to steeper slopes or terrain without the weak layer can provide fun recreation opportunities with significantly higher safety margins. The snowpack conditions are improving, and bigger, steeper terrain will still be here after the persistent slab problem goes away. 

CURRENT CONDITIONS  CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
0600 temperature: deg. F.
Max. temperature in the last 24 hours: deg. F.
Average wind direction during the last 24 hours:
Average wind speed during the last 24 hours: mph
Maximum wind gust in the last 24 hours: mph
New snowfall in the last 24 hours: inches
Total snow depth: inches
Two-Day Mountain Weather Forecast  Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
  Friday Friday Night Saturday
Weather: Mostly cloudy then becoming partly cloudy. Slight chance of snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 10%. Partly cloudy then becoming clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 35 to 40. deg. F. 17 to 23. deg. F. 33 to 38. deg. F.
Wind direction: Southwest 15 to 25 mph with gusts to 45 mph. West around 15 mph with gusts to 30 mph in the evening becoming light. Light winds.
Wind speed:
Expected snowfall: 20% probability up to 1 inch. 80% probability no accumulation. | SWE = less than 0.10 inch. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. in.
For 8000 ft. to 9000 ft.
  Friday Friday Night Saturday
Weather: Mostly cloudy then becoming partly cloudy. Slight chance of snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 10%. Partly cloudy then becoming clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 31 to 37. deg. F. 16 to 21. deg. F. 30 to 36. deg. F.
Wind direction: Southwest 25 to 35 mph increasing to 30 to 45 mph in the afternoon. Gusts up to 90 mph. West 20 to 35 mph. Gusts up to 85 mph decreasing to 60 mph after midnight. Northeast around 15 mph with gusts to 35 mph.
Wind speed:
Expected snowfall: 20% probability up to 1 inch. 80% probability no accumulation. | SWE = less than 0.10 inch. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. in.
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