THIS AVALANCHE FORECAST EXPIRED ON January 16, 2019 @ 6:59 am
Avalanche Forecast published on January 15, 2019 @ 6:59 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

3pm UPDATE - Due to higher than forecasted snowfall amounts the avalanche danger has increased to CONSIDERABLE. The avalanche danger will remain CONSIDERABLE through the night. Check back at 7 am tomorrow for the next update.

 MODERATE avalanche danger will continue. Large persistent slabs remain a concern. Wind slabs and storms slabs could become possible this afternoon and during the night as new snow and wind impact the region.

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: Persistent Slab
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No persistent slab avalanches have been reported since the one on Castle Peak on Jan 11. Significant uncertainty about how widespread this problem may be or how large a trigger it would take to release such a slab still exists. Some data still indicates that fractures could still propagate along the buried persistent weak layer (facets) and some data indicates that this layer may be dormant in many areas. The additional snow load expected this week could reactivate this weak layer in some areas.   

While the likelihood of triggering a persistent slab avalanche may be low, the consequences of a large destructive avalanche are high. Pay close attention to areas where large triggers like cornices looming above a slope may exist and make a plan with your group to manage terrain with appropriate safety margins.  

Avalanche Problem 2: Wind Slab
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New wind slabs will start to form as new snow and wind impact the forecast area. These should remain small during the day due to limited snow accumulation and less strong winds. As snow accumulation and winds increase this afternoon/evening, wind slabs will quickly grow in size and become more widespread during the night. Natural wind slab avalanches will become possible tonight.

Avalanche Problem 3: Storm Slab
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Light snowfall with light winds since yesterday may have buried and preserved the widespread surface hoar layer. This layer of weak feathery snow could serve as a weak layer as more snow accumulates on top of it. Storm slab avalanches that fail on this layer or on other new snow weaknesses could become possible later this afternoon/evening and could grow in size and distribution during the night. Natural storm slab avalanches will become possible tonight.

recent observations

* Snowpit tests and observations targetting the old weak snow layers (facets) on Castle Peak, Hidden Peak, and in Johnson Canyon yielded variable results consistent with other data collected in various locations since Jan 11. Some tests and data showed a dormant weak layer with no signs of instability and some indicated that if this layer breaks fractures could still propagate through the facets. All data indicates that it would take a very large trigger to initiate such a break. 

* Fragile feathery surface snow (surface hoar) existed on top of the snowpack in open areas in Johnson Canyon, Ward Canyon, Chief Creek, and Hidden Peak yesterday. Observers also found it to be widespread in areas along Donner Summit, Echo Summit, and in the Carson Range east of Lake Tahoe on Sunday.

Weather and CURRENT CONDITIONS
weather summary

The winds shifted towards the south as light snow showers started last night. Snowfall amounts varied with most sensors reported a trace to 1 inch with a few stations reporting up to 2 inches. Snow showers should continue this morning and should increase in intensity this afternoon through midnight tonight. The forecast calls for up to another foot of new snow by tomorrow morning with some places receiving even more. Most of this snow should fall between 4 pm and midnight tonight. Winds should start to increase and shift more towards the SW. Tomorrow brings a short break in the weather before a larger winter storm arrives on Wednesday night. Check in with the Reno NWS for more details.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 20 to 25 deg. F.
Max. temperature in the last 24 hours: 26 to 30 deg. F.
Average wind direction during the last 24 hours: NE shifting to S and SSW
Average wind speed during the last 24 hours: 20 to 25 mph
Maximum wind gust in the last 24 hours: 49 mph
New snowfall in the last 24 hours: up to 2 inches
Total snow depth: 46 to 52 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy. Slight chance of snow in the morning, then snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 80%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 100%. Mostly cloudy. Scattered snow showers. Snow levels below 7000 feet. Chance of precipitation is 50%.
Temperatures: 28 to 33 deg. F. 25 to 30 deg. F. 32 to 38 deg. F.
Mid Slope Winds: South 10 to 15 mph with gusts to 25 mph. South 15 to 25 mph. Gusts up to 30 mph increasing to 40 mph after midnight. South 15 to 30 mph. Gusts up to 45 mph.
Expected snowfall: 80% probability of 1 to 3 inches. 20% probability of 3 to 6 inches. | SWE = up to 0.25 inch. 70% probability of 5 to 8 inches. 30% probability of 8 to 12 inches. | SWE = 0.50-0.85 inch. 60% probability of 1 to 2 inches. 40% probability of 2 to 4 inches. | SWE = 0.15-0.25 inch.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy. Slight chance of snow in the morning, then snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 80%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 100%. Mostly cloudy. Scattered snow showers. Snow levels below 7000 feet. Chance of precipitation is 55%.
Temperatures: 23 to 29 deg. F. 21 to 26 deg. F. 26 to 31 deg. F.
Ridge Top Winds: South 15 to 30 mph. Gusts up to 40 mph increasing to 55 mph in the afternoon. South 20 to 35 mph with gusts to 80 mph. Southwest 30 to 45 mph shifting to the south 35 to 60 mph in the afternoon. Gusts up to 105 mph.
Expected snowfall: 70% probability of 2 to 4 inches. 30% probability of 4 to 7 inches. | SWE = up to 0.30 inch. 70% probability of 6 to 12 inches. 30% probability of 12 to 17 inches. | SWE = 0.55-0.85 inch. 60% probability of 1 to 3 inches. 40% probability of 3 to 5 inches. | SWE = up to 0.40 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