THIS AVALANCHE FORECAST EXPIRED ON January 19, 2020 @ 6:59 am
Avalanche Forecast published on January 18, 2020 @ 6:59 am
Issued by Brandon Schwartz - Tahoe National Forest

A worrisome persistent slab avalanche problem exists below treeline and near treeline. Lingering unstable slabs of wind drifted snow may exist above treeline and near treeline. Warming air temperatures today may also trigger some loose wet snow instability. CONSIDERABLE avalanche danger continues below treeline and near treeline with MODERATE avalanche danger above treeline.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

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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Lingering unstable slabs of wind drifted snow remain possible today in above treeline and near treeline lee areas mainly on NW-N-NE-E-SE aspects. Avalanche size up to D2 is expected.

The wind direction has not changed so use the clues of cornice formations, wind pillows, snow surface cracking, and any signs of recent avalanches to determine where unstable wind slabs are most likely to be encountered. Make a plan and discuss it within your group for how to travel around these specific areas with caution.

Avalanche Problem 2: Persistent Slab
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Ongoing instability associated with the buried Jan 4 crust/facet weak layer has now transitioned from a storm slab problem to a persistent slab problem. The Jan 4 crust/facet weak layer exists near treeline and below treeline on NW-N-NE-E aspects. In most below treeline locations, it is found about 2 feet below the snow surface. In some near treeline locations, it is found deeper under older wind drifted snow.

While the likelihood of triggering an avalanche on this weak layer has decreased since the peak of the storm, it is still possible and the consequences of being caught in a below treeline avalanche of this type may not be survivable. Unless there is an extremely clean runout, you will almost certainly have a high force impact with trees. Avalanche size is expected at D2, but do not underestimate how far the avalanche may travel.

If you encounter signs of recent avalanches near to below treeline, evidence of snow surface cracking, snowpack collapse (possible whumpf sound), or unstable snowpit test results, avoid travel on or below steep slopes in the area. An avalanche of this type could easily fracture above and behind you. Previous tracks are not an indication of stability.

If you want to avoid this avalanche problem altogether, select terrain with a maximum slope angle under 30 degrees and without steeper terrain above or to the side. The quality of the snow is so good right now that these lower angle slopes are providing excellent skiing, snowmobiling, and snowboarding experiences.

Avalanche Problem 3: Loose Wet
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Air temperatures rising well above freezing today may create some minor snow surface melt and loose wet snow instability. Rollerballs occurring on steep slopes is a clue to the presence of this avalanche problem. Avalanche size is expected at D1. Most consequences would occur from being pushed over cliffs, into rocks, trees, or terrain traps below.

recent observations
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* A recent natural avalanche was reported yesterday on Angora Peak (Echo Summit/Fallen Leaf Lake area), below treeline on a N aspect at approximately 7,300'. Snowpack collapse with whumpfing and shooting cracks was reported in the adjacent terrain. Other details are unknown, but this has the signature of the current persistent slab avalanche problem.

* The Jan 4 crust/facet weak layer is showing continued instability in many areas. Skier triggered snowpack collapse with whumpfing was reported yesterday from the Pole Creek, Deep Creek, and Echo Summit/Fallen Leaf Lake areas. Unstable snowpit tests indicating continued likely propagation along this layer were reported from the Independence Lake, Donner Summit, Luther Pass, and Carson Pass areas.

* The Jan 4 crust/facet weak layer is most prevalent in the 7,000' to 8,500' elevation range but has been observed with concerning weakness in more isolated distribution at higher elevations.

* Ongoing wind slab instability was inconsistent around the forecast area yesterday with continued unstable wind slabs in some areas and limited evidence of unstable wind slabs in other areas.

Weather and CURRENT CONDITIONS
weather summary

High pressure continues to build over the forecast area. Ridgetop winds remain out of the SW and are light to moderate in speed. Periods of sun mixed with mid to high level cloud cover are forecast to continue today. Air temperatures are expected to climb above freezing today for most locations below 10,000'. A moderate speed E wind event is forecast for Sunday with a few degrees of additional daytime warming over the upper elevations.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 22 to 30 deg. F.
Max. temperature: 25 to 32 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 21 mph
Maximum ridgetop wind gust: 30 mph
New snowfall: 0 inches
Total snow depth: 48 to 64 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 then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 38 to 44. deg. F. 18 to 23. deg. F. 38 to 44. deg. F.
Mid Slope Winds: Light winds. Gusts up to 25 mph in the morning. Light winds. Light winds.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 34 to 40. deg. F. 19 to 24. deg. F. 37 to 43. deg. F.
Ridge Top Winds: Southwest 15 to 25 mph. Gusts up to 45 mph decreasing to 35 mph in the afternoon. Light winds becoming southeast around 15 mph with gusts to 25 mph after midnight. East 15 to 25 mph. Gusts up to 25 mph increasing to 40 mph in the afternoon.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. 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