THIS AVALANCHE FORECAST EXPIRED ON February 6, 2019 @ 6:59 am
Avalanche Forecast published on February 5, 2019 @ 6:59 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

CONSIDERABLE avalanche danger exists at all elevations due to widespread wind slabs and some storm slabs. Large human-triggered avalanches could occur today. More avalanche fatalities occur at the CONSIDERABLE danger rating than at higher danger ratings.

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 winds and several feet of new snow during this storm have left large wind slabs on leeward slopes. Some additional snow and moderate winds in the forecast today may add to these existing wind slabs. While the decrease in storm intensity should have decreased the chances for widespread natural avalanche activity, human-triggered wind slab avalanches remain likely today and some natural wind slabs may still be possible. Wind slab avalanches could be large and destructive. The largest and most fragile wind slabs should exist on wind-loaded NW-N-NE-E-SE aspects in near and above treeline terrain, but some may also exist in wind-exposed areas in below treeline terrain due to the pervasive SW winds. 

Cornices above a slope, blowing snow, wind drifts/pillows, and other wind created textures can help identify where wind slabs may exist. Using this information to plan a cautious route around potential wind slabs with conservative buffer zones represents a prudent choice for today. Less wind-exposed and/or lower angle terrain should hold softer less variable snow.

Avalanche Problem 2: Storm Slab
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Changing conditions during the storm have deposited a variety of storm snow layers. Some of these could serve as weak layers and some could represent slab layers. Human triggered storm slab avalanches will remain possible today on steep slopes in sheltered terrain. The likelihood of natural storm slab activity should have decreased as the storm intensity waned and as temperatures have steadily declined. Some loose dry sluffs could also occur in the new snow on steep slopes today. Storm slab avalanches could be large today especially if they break on one of the deeper weaknesses within the storm snow.  

Before committing to any slopes, look for clues about potential storm slab instability like recent avalanche activity, cracking and collapsing, and/or results on test slopes. Use this information to identify areas where storm slabs may exist and build appropriate safety margins around this problem. Sticking to lower angle terrain without overhead hazard could be one way to have fun with a nice safety margin. 

recent observations

* Observations from Donner Ridge and Incline Lake Peak yesterday found blizzard conditions with intense blowing snow and gale force winds. Widespread skier-triggered shooting cracks occurred in wind-affected areas in both places. On Incline Lake Peak, cornices above test slopes failed easily. On Donner Ridge wind slabs extended into some treed areas.

* In more sheltered areas on Incline Lake Peak and Donner Ridge, deep storm snow existed with several different layers including light snow below heavy snow and some other storm snow weaknesses. One ECTP result was reported from Incline Lake Peak on a density change. 

* Other observations during this storm have also found reactive wind slabs as well as weaknesses in the storm snow. 

Weather and CURRENT CONDITIONS
weather summary

This storm dropped another 18 to 25 inches of new snow across the forecast area in the last 24 hours with some areas reporting ~30 inches. That additional snowfall brings storm totals to 4 to 6 ft in most places with more than that in some areas. The most intense part of the storm should have passed and snow intensity and wind speeds started to decrease after midnight last night. The forecast calls for snow showers to continue today with another 3 to 7 inches of snow in the mountains. Expect cold temperatures as well. This storm should come to an end tonight leaving lighter winds, cold temperatures, and dry weather for tomorrow. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 5 to 12 deg. F.
Max. temperature in the last 24 hours: 19 to 25 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 45 to 55 mph
Maximum wind gust in the last 24 hours: 120 mph
New snowfall in the last 24 hours: 18 to 25 inches
Total snow depth: 106 to 123 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Cloudy. Snow showers. 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 30%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%.
Temperatures: 15 to 20 deg. F. 5 to 11 deg. F. 23 to 28 deg. F.
Mid Slope Winds: West 10 to 15 mph with gusts to 35 mph. West 10 to 15 mph in the evening becoming light. Gusts up to 30 mph. Light winds becoming northwest 10 to 15 mph in the afternoon. Gusts up to 30 mph.
Expected snowfall: 80% probability of 3 to 7 inches. 20% probability of 7 to 10 inches. | SWE = 0.15-0.25 inch. 30% probability up to 1 inch. 70% probability up to 2 inches. | SWE = less than 0.10 inch. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Cloudy. Snow showers. 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 30%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%.
Temperatures: 10 to 15 deg. F. 2 to 7 deg. F. 18 to 24 deg. F.
Ridge Top Winds: West 15 to 25 mph. Gusts up to 50 mph decreasing to 40 mph in the afternoon. West 15 to 20 mph with gusts to 30 mph. West 15 to 25 mph. Gusts up to 35 mph increasing to 45 mph in the afternoon.
Expected snowfall: 80% probability of 3 to 7 inches. 20% probability of 7 to 11 inches. | SWE = 0.15-0.40 inch. 30% probability up to 1 inch. 70% probability up to 2 inches. | 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