THIS AVALANCHE FORECAST EXPIRED ON January 10, 2019 @ 6:54 am
Avalanche Forecast published on January 9, 2019 @ 6:54 am
Issued by Brandon Schwartz - Tahoe National Forest

CONSIDERABLE avalanche danger exists today at all elevations. Wind slab, persistent slab, and possibly storm slab avalanche problems are expected in the backcountry. Large high consequence avalanches could occur today.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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New snow and wind will combine to create new wind slabs today. The vast majority of wind slabs will form near treeline and above treeline on NW-N-NE-E-SE aspects. Avalanche size up to D2 is possible (large enough to bury a person).

Identify and move cautiously around areas where drifting snow is depositing, especially on or below slopes with cornice features or wind pillows. This is the most likely avalanche problem today but the persistent slab problem is more worrisome.

Avalanche Problem 2: Persistent Slab
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The possibility of a large and destructive persistent slab avalanche is worrisome today (size D3). New snow loading on top of a weak layer with a high degree of uncertainty makes for challenging route finding both uphill and down. The often deeper than expected and wider than expected failure of persistent slab avalanches adds additional exposure from terrain either above or to the side. Becoming caught in a persistent slab avalanche today may not be survivable. Be conservative with terrain selection. If snowpack collapse, whumpfing, or other signs of deep instability are encountered, avoid avalanche terrain including low angle areas with steeper slopes above.

The problematic weak layer is faceted snow found below the 2 to 4 feet of recent storm snow deposited 1/5-1/7. This layer is most prominent along the Sierra Crest on northerly aspects between 7,000' and 8,000' in below treeline and near treeline terrain. Isolated areas of ongoing instability have been observed with easier triggering where this weak layer is buried just a couple feet deep. The additional new snowfall today is adding additional stress to this weak layer.

Avalanche Problem 3: Storm Slab
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A storm slab avalanche problem may form today above 7,000' in any areas that receive close to a foot of new snow. If this problem forms it will be found in wind protected areas near treeline or below treeline on any aspect. Avalanche size up to D2 (large enough to bury a person) may occur in isolated areas.

Look for snow surface cracking of just the new snow in wind protected areas as a sign of instability associated with this avalanche problem.

recent observations

* Faceted snow found 2 to 4 feet below the recent storm snow continues to be problematic in isolated areas. Yesterday a party triggered a large snowpack collapse with a whumpf sound on Elephant's Hump near Red Lake (Carson Pass area) on a NE aspect at 7,800'. An avalanche course traveling in Shirley Canyon (Outside Squaw Valley) also reported triggering several collapses with a whumpf sound. Other parties looking at this same weak layer in various other Sierra Crest locations found limited evidence of ongoing instability indicating increased uncertainty. Please continue to report your findings associated with this weak layer.

* Rapid settlement of recent storm snow has made the upside-down upper snowpack from the tail end of the 1/5-1/7 storm cycle more supportable.

Weather and CURRENT CONDITIONS
weather summary

A storm system is moving through the forecast area today. Snow level appears to be around 6,300' to 6,500' this morning. Total snow accumulation of 6" to 12" is expected by this evening above 7,000'. Strong to gale force ridgetop winds out of the S to SW are expected to last through today before decreasing tomorrow. After snowfall tapers off tonight, a quiet weather pattern is expected through Friday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 26 to 30 deg. F.
Max. temperature in the last 24 hours: 33 to 40 deg. F.
Average wind direction during the last 24 hours: SSW
Average wind speed during the last 24 hours: 40 mph
Maximum wind gust in the last 24 hours: 92 mph
New snowfall in the last 24 hours: 4 to 6 inches
Total snow depth: 40 to 55 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy. Snow in the morning, then chance of snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 100%. Mostly cloudy. Chance of snow showers through the night. Snow levels below 7000 feet. Chance of precipitation is 25%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 33 to 38. deg. F. 22 to 28. deg. F. 35 to 40. deg. F.
Mid Slope Winds: South 15 to 30 mph with gusts to 55 mph. Southwest 15 to 25 mph. Gusts up to 45 mph in the evening. Light winds.
Expected snowfall: 80% probability of 3 to 6 inches. 20% probability of 1 to 3 inches. | SWE = 0.20-0.45 inch. 90% probability up to 1 inch. 10% probability no accumulation. | SWE = less than 0.10 inch. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy. Snow in the morning, then chance of snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 100%. Mostly cloudy. Chance of snow showers. Snow levels below 7000 feet. Chance of precipitation is 25%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 30 to 34. deg. F. 20 to 25. deg. F. 33 to 38. deg. F.
Ridge Top Winds: South 35 to 55 mph with gusts to 95 mph. Southwest 25 to 35 mph decreasing to 15 to 25 mph after midnight. Gusts up to 60 mph. Southeast 10 to 15 mph with gusts to 35 mph.
Expected snowfall: 80% probability of 3 to 7 inches. 20% probability of 1 to 3 inches. | SWE = 0.25-0.50 inch. 90% probability up to 1 inch. 10% probability no accumulation. | SWE = less than 0.10 inch. No accumulation. | SWE = none.
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