THIS AVALANCHE FORECAST EXPIRED ON January 24, 2020 @ 6:49 am
Avalanche Forecast published on January 23, 2020 @ 6:49 am
Issued by Brandon Schwartz - Tahoe National Forest

Snowpack stability is improving, but a low likelihood high consequence persistent slab avalanche problem lingers below treeline and near treeline. Warming conditions and light rain on snow this afternoon and tonight below 8,000' may trigger some rollerballs and very small loose wet snow avalanches. MODERATE avalanche danger continues below treeline and near treeline with LOW avalanche danger above treeline.

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

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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Below treeline and near treeline NW-N-NE-E aspects remain the areas of concern. The Jan 4 crust/facet persistent weak layer in these areas is slowly gaining strength but has not fully stabilized. In most below treeline locations, this weak layer is buried 1 to 2 feet below the snow surface. In some near treeline areas, this weak layer is buried up to 8 feet below the surface under wind drifted snow. Human triggered avalanches size D2 to D3 have moved down to unlikely on a regional scale, but isolated instability is still a consideration.

A low likelihood high consequence avalanche problem is what we are working with at this time. The persistent Jan 4 crust/facet weak layer is gaining strength, but not at the same rate in all locations. We are not quite past this avalanche problem on a regional scale. Make conservative terrain and route selections in any areas where unstable snowpit test results or other signs of instability exist.

Avalanche Problem 2: Loose Wet
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Light rain on snow this afternoon and tonight below 8,000' may trigger some rollerballs or very small loose wet avalanches. Avalanche size is expected at D1. Problematic consequences of being caught would come from downslope terrain hazards such as cliffs and terrain traps below.

recent observations
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* Wind slabs observed yesterday on Mt. Judah in lee areas near and above treeline were 4 to 12 inches thick and difficult to trigger. Cornices collapsed with moderate difficulty and did not cause wind slab failure on test slopes.

* The last reported persistent slab avalanche occurred 4 days ago.

* Snowpit tests targeting the persistent Jan 4 crust/facet layer have shown increasingly variable results over the past several days and fewer unstable results.

Weather and CURRENT CONDITIONS
weather summary

A weak weather system will affect the forecast area today. This morning, expect increasing cloud cover, light to moderate speed SW ridgetop winds, and warming air temperatures ahead of the approaching system. Light precipitation is expected to begin this afternoon and last into tomorrow morning. Snow levels are forecast to rise to 7,500' this afternoon and to 8,000' tonight. Snow level is then expected to lower to 7,000' tomorrow morning. For tomorrow expect decreasing cloud cover and moderate speed SW ridgetop winds.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 26 to 37 deg. F.
Max. temperature: 38 to 44 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 14 mph
Maximum ridgetop wind gust: 40 mph
New snowfall: 0 inches
Total snow depth: 43 to 54 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Partly cloudy then becoming mostly cloudy. Isolated showers in the afternoon. Snow levels below 7000 feet increasing to 7500 feet in the afternoon. Chance of precipitation is 20%. Cloudy. Scattered showers. Snow levels 8000 feet. Chance of precipitation is 35%. Mostly cloudy. Isolated showers in the morning. Snow levels 7000 feet. Chance of precipitation is 15%.
Temperatures: 40 to 45. deg. F. 28 to 33. deg. F. 38 to 43. deg. F.
Mid Slope Winds: Light winds. Light winds becoming southwest around 15 mph after midnight. Gusts up to 30 mph. Southwest around 15 mph in the morning becoming light. Gusts up to 30 mph.
Expected snowfall: Little or no accumulation. | SWE = less than 0.10 inch. 30% probability up to 1 inch. 70% probability no accumulation. | SWE = up to 0.10 inch. No accumulation. | SWE = less than 0.10 inch.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Partly cloudy then becoming mostly cloudy. Isolated snow showers in the afternoon. Snow levels below 7000 feet increasing to 7500 feet in the afternoon. Chance of precipitation is 20%. Cloudy. Scattered showers. Snow levels 8000 feet. Chance of precipitation is 35%. Mostly cloudy then becoming partly cloudy. Isolated snow showers in the morning. Snow levels 7000 feet. Chance of precipitation is 15%.
Temperatures: 35 to 41. deg. F. 26 to 31. deg. F. 35 to 41. deg. F.
Ridge Top Winds: Southwest 10 to 20 mph with gusts to 30 mph. Southwest 15 to 25 mph. Gusts up to 30 mph increasing to 45 mph after midnight. Southwest 15 to 30 mph with gusts to 60 mph.
Expected snowfall: Little or no accumulation. | SWE = less than 0.10 inch. 70% probability up to 2 inches. 30% probability of 2 to 4 inches. | SWE = up to 0.20 inch. Up to 1 inch. | SWE = less than 0.10 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