THIS AVALANCHE FORECAST EXPIRED ON January 19, 2019 @ 6:43 am
Avalanche Forecast published on January 18, 2019 @ 6:43 am
Issued by Brandon Schwartz - Tahoe National Forest

CONSIDERABLE avalanche danger exists at all elevations due to a wind slab avalanche problem and uncertainty associated with continued storm slab and deep slab avalanche problems. Large destructive avalanches remain possible 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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Gale force SW winds combined with feet of recent storm snow has created large wind slabs. The vast majority of wind slabs exist in near treeline and above treeline areas on NW-N-NE-E-SE aspects. Wind slabs may be encountered to a lesser extent on other aspects and/or in below treeline areas. Cornices present an additional hazard and may collapse easily today.

Significant hazard remains today on slopes below or adjacent to cornice features or wind pillows. Be conservative around these areas and keep a wide margin of safety.

Avalanche Problem 2: Storm Slab
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Significant uncertainty exists as to the ongoing instability of 2 to 4 foot thick storm slabs on top of a weak layer of surface hoar. Both natural and human triggered avalanches were fairly widespread on this weak layer two days ago. Data collection was limited yesterday due to access difficulties.

In any areas where surface hoar remains an active weak layer, avalanche activity could occur in lower angle terrain, well below ridgetops. Many of these areas where avalanche activity already has and may continue to occur are traditionally thought of a safe terrain. Slope angle is everything with this avalanche problem. Approach NW-N-NE-E aspect terrain with cautious route-finding. If any signs of ongoing instability are encountered including recent avalanche activity, cracking, collapse, whumpfing sounds, or unstable snowpit test results, avoid exposure to avalanche terrain including low angle slopes connected to steeper terrain above.

Avalanche Problem 3: Deep Slab
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Uncertainty remains for ongoing instability associated with a deep slab avalanche problem. The previously problematic weak layer of crust and faceted snow is now buried 4 to 12+ feet deep in Sierra Crest locations on NW-N-NE-E aspects.

Large destructive avalanches could be created by large triggers such as cornice collapse or deeper than normal triggers such as sinking deep into the snowpack on foot or deep trenching snowmobiles. Keep in mind that the large avalanche size would be very difficult to survive due to associated trauma and/or deep burial depth. Choosing smaller simple terrain without rocks and cliffs that is not capable of producing a large avalanche is a way to help mitigate this avalanche problem.

recent observations

* Numerous wind slab and storm slab avalanches both natural and human triggered were reported within the forecast area over the past two days both above and below treeline.

* Avalanches involving a weak layer of buried surface hoar were remotely triggered from low angle terrain in open areas well below treeline.

* Snowpack depth above 7,000' increased by 2 to 4.5 feet in most areas over the past couple of days.

Weather and CURRENT CONDITIONS
weather summary

The strong storm system from the past few days is exiting the region. The next weather disturbance is currently moving cloud cover and humid air into the forecast area. Light snow showers may occur at times today with snow level rising to 8,000' by this evening. Partial clearing is forecast for tomorrow before another storm system impacts the region on Sunday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 21 to 26 deg. F.
Max. temperature in the last 24 hours: 25 to 30 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 69 mph
Maximum wind gust in the last 24 hours: 140 mph
New snowfall in the last 24 hours: 7 to 14 inches
Total snow depth: 71 to 95 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 35%. Mostly cloudy. Chance of snow showers in the evening. Slight chance of showers after midnight. Snow levels rising to 8000 feet. Chance of precipitation is 20%. Mostly cloudy then becoming partly cloudy. Slight chance of showers in the morning. Snow levels 8000 feet. Chance of precipitation is 10%.
Temperatures: 34 to 39. deg. F. 29 to 33. deg. F. 40 to 45. deg. F.
Mid Slope Winds: West winds around 10 mph. Gusts up to 25 mph in the morning. Southwest 10 to 15 mph with gusts to 40 mph. Southwest 10 to 15 mph. Gusts up to 30 mph.
Expected snowfall: 80% probability up to 1 inch. 20% probability 1 to 2 inches. | SWE = less than 0.10 inch. 20% probability up to 2 inches. 80% probability no accumulation. | SWE = up to 0.15 inch. No accumulation. | SWE = less than 0.10 inch.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 35%. Mostly cloudy. Slight chance of showers. Snow levels rising to 8000 feet. Chance of precipitation is 20%. Mostly cloudy then becoming partly cloudy. Snow levels 8000 feet. Chance of precipitation is 10%.
Temperatures: 30 to 34. deg. F. 28 to 33. deg. F. 37 to 42. deg. F.
Ridge Top Winds: Southwest 15 to 30 mph with gusts to 65 mph. West 20 to 35 mph with gusts to 65 mph. Southwest 15 to 25 mph. Gusts up to 45 mph decreasing to 35 mph in the afternoon.
Expected snowfall: 70% probability up to 1 inch. 30% probability of 1 to 3 inches. | SWE = less than 0.10 inch. 20% probability up to 2 inches. 80% probability no accumulation. | SWE = up to 0.15 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