THIS AVALANCHE FORECAST EXPIRED ON March 20, 2020 @ 7:00 am
Avalanche Forecast published on March 19, 2020 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

Wind-loaded near and above treeline terrain still holds fragile cornices and slabs of wind drifted snow. People can still trigger wind slab avalanches in these areas. Triggering a deep slab avalanche is becoming unlikely but may not be impossible in some isolated near and below treeline terrain where old weak snow lurks below the storm snow. MODERATE avalanche danger exists at all elevations. 

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: Wind Slab
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Despite the decrease in wind, expect to find slabs of wind drifted snow and fragile cornices lingering on wind-loaded and cross-loaded NW-N-NE-E-SE aspects. These wind slabs should be slightly more difficult to trigger today, but some of them could still break several feet deep and could involve enough snow to bury a person or a car (D2-D3).

Smooth pillows of wind drifted snow on a slope, scoured areas on the ridge above a slope, and cornices hanging over the slope can all indicate the presence of wind slabs. Identifying where unstable wind slabs may exist can help reduce your exposure to this avalanche problem. Areas sheltered from the winds will hold softer less wind-affected snow. 

Avalanche Problem 2: Deep Slab
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Weak sugary snow still exists underneath 3 to 5 ft of new snow in some areas on near and below treeline NW-N-NE aspects. On Sunday parties reported whumpfing on this layer and one avalanche may have occurred on Powderhouse Peak. Since then, signs of instability have decreased and evidence now indicates that getting enough force through the upper snowpack to break this layer would be difficult. Triggering a deep slab avalanche may be unlikely at this point, but it is not impossible especially with a larger trigger like multiple people on the same slope or a large cornice failure or with a smaller trigger at just the right spot/trigger point on some isolated slope. If a deep slab avalanche were to occur it would be very large and entrain all of the recent snow. 

Due to the consequences of an unlikely but not impossible deep slab avalanche and some degree of uncertainty around this problem, it still warrants careful consideration. Identify where this layer may exist by probing into the snowpack or digging a snowpit. Recent avalanches, whumpfing, or snowpack collapse can indicate that you have found an isolated area where the deep slab instability remains active. If you have any doubts about the potential for a deep slab, go ahead choose a different aspect or more conservative terrain. 

recent observations
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* A report came in of a skier triggered deep slab on 3/15 at Powderhouse Peak.

* Yesterday skier triggered avalanches were reported on Tallac and Incline Lake Peak. These were most likely wind slab on wind loaded N facing terrain on Tallac and cross-loaded SE facing terrain on Incline Lake Peak. Small new wind slabs also were reported on test slopes on Fireplug and Incline Lake Peak yesterday.

* Tests targetting the facet layer below the new snow on Elephants Back and on Incline Lake Peak indicated that triggering this layer would be difficult but that if it does break fractures may still be able to propagate along the layer.

* Observations show the storm snow continuing to consolidate.

Weather and CURRENT CONDITIONS
weather summary

Snow showers started to dissipate yesterday afternoon/evening and winds shifted to the E and NE and decreased during the night. The lingering low pressure should continue to weaken today, but the forecast still calls for cloudy conditions with some light snow showers. Winds should remain light. By tomorrow a slight warming and clearing trend should begin as the low-pressure continues to weaken.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 11 to 18 deg. F.
Max. temperature: 19 to 29 deg. F.
Average ridgetop wind direction: SW until ~11pm last night then E and NE
Average ridgetop wind speed: SW: 20 to 30 mph | E & NE 5 to 10 mph
Maximum ridgetop wind gust: 56 mph
New snowfall: 2 to 4 inches
Total snow depth: 63 to 92 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 then becoming partly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 30%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%. Partly cloudy. Slight chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 15%.
Temperatures: 28 to 33 deg. F. 13 to 19 deg. F. 32 to 37 deg. F.
Mid Slope Winds: Light winds. Light winds. Light winds.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. No accumulation. | SWE = none. No accumulation. | SWE = trace amounts.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy then becoming partly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 40%. Partly cloudy. Slight chance of snow early. Snow levels below 7000 feet. Chance of precipitation is 15%. Partly cloudy. Slight chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 15%.
Temperatures: 22 to 28 deg. F. 10 to 16 deg. F. 27 to 33 deg. F.
Ridge Top Winds: Light winds. Light winds. Light winds becoming east around 15 mph in the afternoon.
Expected snowfall: Up to one inch. | SWE = less than 0.10 inch. No accumulation. | SWE = trace amounts. No accumulation. | SWE = trace amounts.
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