THIS AVALANCHE FORECAST EXPIRED ON January 26, 2020 @ 6:53 am
Avalanche Forecast published on January 25, 2020 @ 6:53 am
Issued by Brandon Schwartz - Tahoe National Forest

Wind drifted snow that has formed into slabs remains an avalanche problem today above treeline and near treeline. A persistent weak layer of crust and sugary faceted snow is keeping isolated instability and a pesky low likelihood high consequence avalanche problem ongoing near treeline and below treeline. Avalanche danger is MODERATE for all elevations.

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: Wind Slab
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Small unstable wind slabs were observed yesterday above treeline. Instability of these slabs of wind drifted snow may linger today. In isolated areas, these wind slabs are on top of surface hoar which may slow the rate of stabilization. The areas of concern for this avalanche problem are near treeline and above treeline on NW-N-NE-E-SE aspects. Avalanche size is expected at D1 to D2. A period of larger wind slab formation will occur tonight with SW wind and new snowfall.

Identify slopes where unstable wind slabs may exist. Use clues such as cornice formations, wind pillows, scouring vs deposition patterns on ridgelines, and areas of snow surface cracking to highlight areas of concern. Communicate within your group a plan for how to move around these areas with caution.

 

Avalanche Problem 2: Persistent Slab
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It would be nice to be done worrying about this avalanche problem, but we're just not there yet. Isolated instability is observed somewhere daily below treeline and near treeline on NW-N-NE-E aspects on the sugary Jan 4 crust/facet persistent weak layer. In most below treeline locations, this weak layer is buried 1 to 2 feet below the snow surface and as much as to 8 feet below the surface near treeline under wind drifted snow. Human triggered avalanches size D2 to D3 have become unlikely on a regional scale, but an isolated avalanche is still a concern. Tonight's rain/snow loading event could make this weak layer more reactive.

A low likelihood high consequence avalanche problem is what remains at this time. Spatial variability of stable vs unstable is increasing. Many areas are stable, others are not. Make conservative terrain and route selections in any areas where unstable snowpit test results or other signs of instability exist.

recent observations
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* Small shallow unstable wind slabs were observed yesterday above treeline in the Carson Pass area on Elephants Back and Red Lake Peak. On Red Lake Peak, skier triggered cracking was observed in wind drifted areas. Looking under these wind slabs revealed that they were on top of surface hoar.

* Surface hoar under wind slabs above about 8,500' that was observed yesterday on Carson Pass may exist in the Luther Pass and Echo Summit areas where surface hoar was observed on Thursday. This was not seen yesterday in the Mount Rose or West Shore Tahoe areas. The presence or absence of surface hoar in other above 8,500' areas is unknown.

* Snowpit tests targeting the persistent Jan 4 crust/facet layer continue to show spatial variability. Unstable test results were reported yesterday from Red Lake Peak (Carson Pass area). Some mixed results were reported yesterday from Scout Peak (Echo Summit area). No persistent slab instability was reported yesterday from Tamarack Peak (Mount Rose area) or from Rubicon Peak (West Shore Tahoe area). Comparing the unstable results from Jan 23 on Stoney Ridge with the lack of instability observed yesterday on adjacent Rubicon Peak demonstrates the spatial variability quite well.

Weather and CURRENT CONDITIONS
weather summary

Increasing cloud cover is expected today ahead of an approaching storm system. Ridgetop winds from the SW are forecast to remain light to moderate today, increasing tonight into tomorrow. The main period of precipitation is expected to begin around midnight and continue through Sunday morning. Snow levels will start high and lower as the storm progresses. Storm total snow amounts are forecast at 6 to 10 inches above 8,000' from 0.5 to 0.8 inches of SWE. Mostly rain followed by a couple of inches of snow is expected at Lake Tahoe level. A break in the weather is expected Sunday night and Monday with short term high pressure.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 28 to 34 deg. F.
Max. temperature: 30 to 36 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 25 mph
Maximum ridgetop wind gust: 91 mph
New snowfall: 0 inches
Total snow depth: 42 to 53 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. Snow levels 7500 feet increasing to 8500 feet in the afternoon. Chance of precipitation is 5%. Cloudy. Chance of rain and snow in the evening, then snow and rain after midnight. Snow levels 8500 feet decreasing to 7500 feet after midnight. Chance of precipitation is 100%. Mostly cloudy. Snow in the morning, then chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 100%.
Temperatures: 42 to 48. deg. F. 28 to 33. deg. F. 33 to 38. deg. F.
Mid Slope Winds: Southwest to west up to 10 mph. Southwest 10 to 20 mph. Gusts to 35 mph after midnight. Southwest 15 to 25 mph with gusts to 35 mph.
Expected snowfall: No accumulation. | SWE = none. 80% probability up to 2 inches. 20% probability of 2 to 5 inches. | SWE = 0.20-0.45 inch. 80% probability of 2 to 4 inches. 20% probability of 4 to 6 inches. | SWE = 0.15-0.25 inch.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy. Snow levels 7500 feet increasing to 8500 feet in the afternoon. Chance of precipitation is 5%. Cloudy. Chance of rain and snow in the evening, then snow after midnight. Snow levels 8500 feet decreasing to 7500 feet after midnight. Chance of precipitation is 100%. Mostly cloudy. Snow in the morning, then chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 100%.
Temperatures: 38 to 44. deg. F. 24 to 30. deg. F. 28 to 34. deg. F.
Ridge Top Winds: Southwest to west 15 to 25 mph with gusts to 35 mph in the morning decreasing to 10 to 20 mph. Southwest 15 to 25 mph with gusts to 35 mph increasing to 25 to 40 mph with gusts to 65 mph after midnight. Southwest 30 to 45 mph decreasing to 20 to 30 mph in the afternoon. Gusts up to 65 mph.
Expected snowfall: No accumulation. | SWE = none. 80% probability of 2 to 4 inches. 20% probability of 4 to 6 inches. | SWE = 0.25-0.50 inch. 80% probability of 2 to 4 inches. 20% probability of 4 to 6 inches. | SWE = up to 0.30 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