THIS AVALANCHE FORECAST EXPIRED ON March 23, 2020 @ 7:03 am
Avalanche Forecast published on March 22, 2020 @ 7:03 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

Pesky ENE winds have left small fresh slabs of wind drifted snow near upper elevation ridgelines. Daytime warming and sunshine may also allow some loose wet avalanche problems to form on lower elevation sunny slopes. On top of these two problems, an unlikely but not impossible deep slab problem still may exist on some isolated near and below treeline slopes. MODERATE avalanche danger continues.

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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Stronger than forecast ENE winds created fresh slabs of wind drifted snow near some upper elevation ridgelines yesterday. Since there is still some snow for transport and those ENE winds picked back up this morning small sensitive wind slabs may still exist on wind-loaded and cross-loaded SE-S-SW-W-NW-N aspects in above treeline terrain. Today's sunshine could make these wind slabs easier to trigger on sun-exposed slopes. 

Blowing snow, smooth pillows of wind drifted snow, and fresh cornices above a slope can help identify where these wind slabs may exist.

Avalanche Problem 2: Loose Wet
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Sunny skies and warmer daytime temperatures could create enough wet surface snow for some loose wet avalanche problems to form once the snow warms up. These issues would be less likely in areas exposed to this morning's ENE winds or in areas where cloud cover develops this afternoon. 

Wet sticky snow, rollerballs, and pinwheels of wet snow indicate that enough warming has occurred for loose wet avalanche problems. Once you see signs of warming like this it is time to find a colder aspect, move to lower angle slopes, or head back home. 

Avalanche Problem 3: Deep Slab
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The recent storm overloaded the weak old snow and resulted in a deep slab avalanche cycle. Observations have trickled in this week, and we can now piece together a deep slab timeline. Several large avalanches released naturally during the storm last Sunday (3/15) and maybe Monday (3/16). Once the storm ended, numerous people have been traveling in the backcountry. Despite the increased backcountry traffic, only a few human-triggered deep slabs have been reported. Some occurred on 3/17 south of the forecast area and one large avalanche occurred on 3/18 (it was not reported until 3/20). One human-triggered deep slab avalanche occurred on isolated terrain features on each of 3/19 and on 3/20. During this time snowpit data has shown a trend for these kinds of avalanches becoming more difficult to trigger.

Most evidence indicates that triggering a deep slab avalanche has become unlikely on a regional scale. That being said, some uncertainty still exists surrounding this problem and it may not be impossible. In the unlikely event that one of these does occur it would be on an isolated terrain feature on a NW-N-NE aspect in near or below treeline terrain where the weak layer exists.  

Due to the consequences of an unlikely but not impossible deep slab avalanche and some degree of uncertainty around this problem, it still warrants consideration. 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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Observers reported 3 small wind slabs near the ridge of the Bronco Chutes on Relay Peak yesterday (more details here). Stronger than forecast E winds created these reactive wind slabs. Another avalanche was reported in Powderhouse Bowl that caught a person. No injuries were reported. No additional details about the avalanche were reported. 

Snowpit tests and other observations from near a deep slab avalanche on Martis Peak that likely occurred on Wednesday 3/18 indicated that triggering that avalanche would be more difficult yesterday but that if the weak layer started to break the resulting fracture might still propagate through that weak layer. 

Snowmobilers reported some rollerballs and pinwheels during the afternoon on sun-exposed slopes around 6000 ft near Wrights Lake.

 

Weather and CURRENT CONDITIONS
weather summary

Yesterday sensors and observers along upper elevation ridges reported ENE winds of 20 to 35 mph and some blowing snow until mid-afternoon. They also reported a trace of new snow in the form of graupel during the afternoon in some places. The winds calmed down in the evening and picked back up to around 20 mph after midnight. The forecast calls for the winds to shift to the SE at upper elevations today and remain light in the lower elevations. Expect clear skies and slightly warmer temperatures for much of the day today. By this afternoon an approaching low pressure could bring some cloud cover and light snow showers to the region especially in areas south of Hwy 50. Another stronger low pressure should move into the area on Monday bringing some additional snow and strong SW winds. 

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 20 to 26 deg. F.
Max. temperature: 28 to 38 deg. F.
Average ridgetop wind direction: ENE
Average ridgetop wind speed: 15 to 20 mph
Maximum ridgetop wind gust: 59 mph
New snowfall: trace to 0 inches
Total snow depth: 57 to 84 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Sunny then becoming partly cloudy. Chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 25%. Mostly cloudy then becoming partly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 25%. Mostly cloudy. Snow likely. Snow levels below 7000 feet. Chance of precipitation is 55%.
Temperatures: 38 to 43 deg. F. 22 to 27 deg. F. 34 to 40 deg. F.
Mid Slope Winds: Light winds. Light winds. Light winds becoming southwest 15 to 25 mph with gusts to 45 mph in the afternoon.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. 80% probability up to 1 inch. 20% probability of 1 to 2 inches. | SWE = less than 0.10 inch. 80% probability up to 2 inches. 20% probability of 2 to 4 inches. | SWE = up to 0.15 inch.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Sunny then becoming partly cloudy. Chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 30%. Mostly cloudy then becoming partly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 30%. Mostly cloudy. Snow likely. Snow levels below 7000 feet. Chance of precipitation is 55%.
Temperatures: 30 to 36 deg. F. 19 to 24 deg. F. 29 to 35 deg. F.
Ridge Top Winds: Southeast around 15 mph with gusts to 25 mph. Light winds becoming southwest around 15 mph with gusts to 25 mph after midnight. West 15 to 20 mph with gusts to 40 mph shifting to the southwest 20 to 30 mph with gusts to 60 mph in the afternoon.
Expected snowfall: Up to 2 inches. | SWE = less than 0.10 inch. 80% probability up to 1 inch. 20% probability of 1 to 2 inches. | SWE = less than 0.10 inch. 80% probability of 1 to 2 inches. 20% probability of 2 to 4 inches. | SWE = up to 0.15 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