THIS AVALANCHE ADVISORY EXPIRED ON April 15, 2016 @ 7:10 am
Avalanche Advisory published on April 14, 2016 @ 7:10 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger could exist on NW-N-NE-E-SE aspects due to a combination of wind slabs in near and above treeline areas and loose dry avalanches. Today's avalanche activity should remain small due to the amount of new snow, but some avalanches could cause problems for backcountry travelers especially north of Tahoe City or near terrain traps. If the sun breaks through the clouds, today some small isolated loose wet avalanches could occur on the near and below treeline SE-S-SW aspects

2. Moderate

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

2. Moderate

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

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Dry
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A dramatic drop in temperatures should have allowed some of this week's wet snow to start to refreeze last night. As this wet snow continues to refreeze during the cold and cloudy weather the snowpack underneath the new snow should gain strength. On the other hand the new snow that fell last night and continues to fall today in some areas may not bond well to the melt-freeze crusts at first especially since many of the old snow surfaces may have frozen before the new snow started to fall. Some loose dry snow sluffs may become possible on steep NW-N-NE-E aspects and on some SE aspects wherever new cold snow has accumulated on top of frozen melt-freeze crusts. Areas north of Tahoe City will hold the best chances for these loose dry sluffs since they received more new snow. These loose dry sluffs should remain small and not entrain much snow due to the paltry amounts of new snow accumulation, but some of them could entrain enough snow to knock a person over or push them off course. These small loose dry sluffs could have larger consequences if they occur in or near terrain traps like gullies, cliffs, creeks, or other places that magnify the consequences of any size avalanche

Avalanche Problem 2: Wind Slab
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Some wind slabs may have formed due to the combination of strong winds and new snow. These wind slabs will also sit above frozen crusts and may not have bonded well to those crusts. Most of these wind slabs should remain small and limited in distribution due to the amount of new snow available for wind loading. Even though many of these wind slabs should not involve enough snow to bury person, some of them could still be large enough to cause problems for backcountry travelers especially north of Tahoe City or in areas where terrain traps like the ones mentioned above exist. Wind loaded N-NE-E aspects and cross loaded NW and SE aspects in near and above treeline terrain north of Tahoe City represent the best places to find human triggerable wind slabs today. 

Avalanche Problem 3: Loose Wet
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Despite the colder temperatures, the strong April sun may be enough for some loose wet avalanches to occur on steep sun-exposed SE-S-SW aspects. If the forecasted cloud cover remains over the area these kind of avalanches should not happen, but if the sun breaks through onto some of these slopes where new cold snow exists some small isolated loose wet avalanches like point releases, roller balls, and pinwheels could occur. 

recent observations

Yesterday observations on Red Lake Peak near Carson Pass showed melt-freeze crusts that varied from supportable to breakable by aspect with a layer of deep wet snow below the crusts. Despite the strong SW winds and slightly cooler daytime highs enough warming occurred on the E-SE-S-SW aspects by noon for the snowpack to become unsupportable and for ski cuts on steep south facing test slopes to cause small loose wet avalanches. Overall observations from around the forecast area this week have shown a snowpack characterized by melt-freeze conditions that should handle new snow loading well as long as some refreezing occurred. 

Weather and CURRENT CONDITIONS
weather summary

Strong southwest winds with gusts into the 70 to 80 mph range accompanied by colder temperatures and snow impacted the region last night and this morning. Snow showers started north of Tahoe City after midnight and spread southward towards Carson Pass by 5 am. Areas around Donner Summit and north have received the most new snow with sensors showing between 2 and 4 inches as of 6 am this morning. Moving south snowfall amounts decreased to only a trace of new snow around Carson Pass and Bear Valley as of 6 am this morning. The southwest winds should remain strong and temperatures should remain cold through tonight. The forecast also calls for snow showers to continue this morning before starting to taper off this afternoon and tonight. These showers could produce up to 3 more inches of snow in areas above 7000 ft. As the storm starts moving eastward tonight the winds should decrease some and shift to the northwest. By tomorrow the forecast calls for partly cloudy skies, daytime highs in the 30's similar to today, and strong northeast winds.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 22 to 26 deg. F.
Max. temperature in the last 24 hours: 36 to 44 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 35 to 50 mph
Maximum wind gust in the last 24 hours: 81 mph
New snowfall in the last 24 hours: North of Tahoe City: 2 to 4 inches | South of Tahoe City: trace to 2 inches
Total snow depth: 61 to 107 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy with snow showers in the morning becoming partly cloudy with scattered snow in the afternoon Mostly cloudy with scattered snow showers in the evening then isolated snow showers after midnight Partly cloudy
Temperatures: 32 to 38 deg. F. 16 to 23 deg. F. 32 to 39 deg. F.
Wind Direction: Southwest West shifting to the northwest after midnight Northeast
Wind Speed: 25 to 35 mph with gusts to 50 mph 25 to 30 mph with gusts to 45 mph decreasing to 15 to 20 mph with gusts to 30 mph after midnight 20 to 25 mph with gusts to 35 mph increasing to 30 to 35 mph with gusts to 50 mph in the afternoon
Expected snowfall: up to 2 in. up to 1 in. 0 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy with snow showers in the morning becoming partly cloudy with scattered snow in the afternoon Mostly cloudy with scattered snow showers in the evening then isolated snow showers after midnight Partly cloudy
Temperatures: 28 to 34 deg. F. 13 to 20 deg. F. 31 to 37 deg. F.
Wind Direction: Southwest West shifting to the northwest after midnight Northeast
Wind Speed: 55 to 60 mph with gusts to 80 mph decreasing to 40 to 45 mph with gusts to 70 mph in the afternoon 40 to 45 mph with gusts to 70 mph decreasing to 25 to 30 mph with gusts to 45 mph after midnight 35 to 40 mph with gusts to 60 mph increasing to 45 to 50 mph with gusts to 70 mph in the afternoon
Expected snowfall: up to 2 in. up to 1 in. 0 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This advisory 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 advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258