THIS AVALANCHE FORECAST EXPIRED ON February 9, 2019 @ 6:58 pm
Avalanche Forecast published on February 9, 2019 @ 6:58 am
Issued by Brandon Schwartz - Tahoe National Forest

CONSIDERABLE avalanche danger exists today in near treeline and above treeline areas due to a wind slab avalanche problem. MODERATE avalanche danger exists below treeline due to possible storm slabs. Please note that this advisory is valid for 12 hours. The next update to this advisory will occur at 7 pm this evening. Increasing avalanche danger is expected tonight.

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Blowing and drifting snow has been occurring for over 24 hours now with additional new snowfall added last night. Newly formed wind slabs exist near treeline and above treeline. These wind slabs are becoming larger in size and more widespread. The vast majority of wind slabs will be encountered on NW-N-NE-E-SE aspects. Isolated wind slabs may also exist in other areas where wind drifted snow is depositing, including below treeline. Wind slab avalanches large enough to bury or injure a person are likely today (size D2).

Identify and avoid specific areas where wind drifted snow is depositing to form wind slabs. Ridgetop areas below cornice features and wind pillows will certainly hold wind slabs today. Snow surface cracking is also a sign of unstable snow.  Move around these areas with a wide margin for error and seek wind sheltered terrain in order to reduce avalanche hazard.

Avalanche Problem 2: Storm Slab
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New snowfall last night and additional snowfall today creates the possibility of storm slab avalanches. This avalanche problem forms in wind protected areas and is possible today near treeline and below treeline on all aspects. Open areas on NW-N-NE aspects where isolated patches of surface hoar were buried under last night's snowfall could have greater sensitivity to triggering. Storm slab avalanches up to size D2 are possible today, especially where new snow amounts approach 1 foot or more.

Continually assess for signs of instability in below treeline avalanche terrain including snow surface cracking and recent avalanche activity. If signs of instability are encountered, be conservative with terrain choices and slope angles. Create wide margins for error.

recent observations

* SSW ridgetop winds began moving and drifting snow near and above treeline yesterday before the start of new snowfall. Reports of blowing snow were received from parties in the Luther Pass, Desolation Wilderness, and Donner Summit areas.

* Two unintentionally skier triggered wind slab avalanches were reported yesterday in near treeline and above treeline terrain on NE-E aspects that traditionally receive efficient wind loading. The avalanches occurred on Mt. Tallac's Corkscrew Bowl (Desolation Wilderness area) and on Mt. Judah's East Face (Donner Summit area).

* No signs of instability were reported yesterday from below treeline areas. This was prior to last night's snowfall.

* A few isolated patches of surface hoar were noted pre-storm in wind protected open areas below treeline yesterday on Trimmer Peak (Luther Pass area).

* The mid level and deeper portions of the snowpack remain well consolidated and without problematic weak layers.

Weather and CURRENT CONDITIONS
weather summary

A weaker but cold storm system moved into the forecast area last night. Light to moderate snowfall is expected to continue today along the Sierra Crest. A more pronounced lull in snowfall may occur over the eastern portion of the forecast area by this afternoon. Ridgetop winds out of the SSW to SW further increased in speed last night. Winds are expected to become even stronger today and tonight with ridgetop gusts 80 to 125 mph. Another round of high intensity snowfall is forecast to begin this evening and continue through the overnight hours with significant accumulations. Ridgetop winds and snowfall intensity are expected to taper down by tomorrow afternoon.

CURRENT CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
6am temperature: 14 to 20 deg. F.
Max. temperature: 16 to 22 deg. F.
Average ridgetop wind direction: SSW
Average ridgetop wind speed: 37 mph
Maximum ridgetop wind gust: 60 mph
New snowfall: 3 to 7 inches
Total snow depth: 91 to 114 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 90%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 100%. Cloudy. Snow in the morning, then chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 80%.
Temperatures: 23 to 28 deg. F. 20 to 25 deg. F. 21 to 26 deg. F.
Mid Slope Winds: Southwest around 15 mph with gusts to 40 mph increasing to 20 to 30 mph with gusts to 60 mph in the afternoon. Southwest 30 to 45 mph with gusts to 90 mph. Southwest 15 to 30 mph. Gusts up to 55 mph decreasing to 40 mph in the afternoon.
Expected snowfall: 90% probability of 6 to 10 inches. 10% probability of 8 to 14 inches. | SWE = 0.25-0.50 inch. 90% probability of 10 to 20 inches. 10% probability of 18 to 26 inches. | SWE = 0.60-1.10 inches. 80% probability of 4 to 8 inches. 20% probability up to 4 inches. | SWE = 0.20-0.45 inch.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 90%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 100%. Cloudy. Snow in the morning, then chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 85%.
Temperatures: 19 to 24 deg. F. 17 to 23 deg. F. 17 to 22 deg. F.
Ridge Top Winds: Southwest 20 to 30 mph increasing to 30 to 45 mph in the afternoon. Gusts up to 80 mph. Southwest 40 to 60 mph with gusts to 125 mph. Southwest 30 to 45 mph with gusts to 95 mph becoming west 20 to 30 mph with gusts to 55 mph in the afternoon.
Expected snowfall: 80% probability of 4 to 12 inches. 20% probability of 12 to 20 inches. | SWE = 0.30 to 0.60 inch. 90% probability of 15 to 25 inches. 10% probability of 20 to 30 inches. | SWE = 0.65 to 1.15 inches. 90% probability of 4 to 8 inches. 10% probability up to 4 inches. | SWE = 0.20-0.45 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

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