THIS AVALANCHE FORECAST EXPIRED ON April 17, 2018 @ 6:48 am
Avalanche Forecast published on April 16, 2018 @ 6:48 am
Issued by Brandon Schwartz - Tahoe National Forest

CONSIDERABLE avalanche danger exists near treeline and above treeline today. MODERATE avalanche danger exists below treeline. Today's wind slab and storm slab avalanche problems have the potential to be exacerbated by rapid warming. Loose wet avalanches are unlikely today, but could become an issue if the sun comes out from behind the clouds. The avalanche situation could be fairly complex in the backcountry today. If in doubt, seek low angle terrain without steeper terrain above.

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: Wind Slab
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New snow combined with strong to gale force SW winds last night are expected to have created new wind slabs near treeline and above treeline on NW-N-NE-E-SE-S aspects. Avalanche size up to D2 is expected (large enough to bury or injure a person). Wind slab instability may be especially problematic today due to two issues beyond the norm: 1) Graupel (pellet snow) was noted in several locations around the forecast area at the onset of yesterday's snowfall. Graupel may be sandwiched at the old/new snow interface between crust below and new wind slab above. In locations where this graupel is a problematic weak layer, it may allow for wider than normal propagation of wind slabs today. 2) Any breaks in cloud cover today will allow for rapid warming of wind slabs that could increase the likelihood of triggering. This potential rapid warming will affect all aspects given the high sun angle this time of year, but would be especially problematic on E-SE-S aspects.

Look for and avoid areas of concern. Identify slopes similar to any in the area with recent avalanche activity. Identify slopes with signs of recently wind drifted snow including cornice or wind pillow formations across the upper portion of the slope. Look for snow surface cracking. Use these clues to identify the slopes most likely to hold unstable snow and choose different terrain.

Avalanche Problem 2: Storm Slab
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New snow deposited in wind protected areas below treeline may allow for problematic storm slabs on all aspects today. Avalanche size up to D2 is possible (large enough to bury or injure a person). The potential graupel layer and rapid warming issues outlined in the wind slab section may also exacerbate storm slab instability today. Look for signs of recent avalanche activity below treeline and snow surface cracking. Pay attention to sun breaks and associated rapid warming. Avoid avalanche terrain in any locations where signs of unstable storm slabs exist.

Avalanche Problem 3: Loose Wet
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Loose wet is an unlikely avalanche problem today, but could be an issue if cloud cover is less than forecast and more sunshine occurs than expected. Pay attention to cloud cover and sun breaks. The more the sun comes out from behind the clouds, the more this will be a problem. Natural or human triggered roller balls will be an indication of a developing loose wet avalanche problem today. If this avalanche problem materializes today, avalanche size up to D2 could occur on any aspect at any elevation (D2 = large enough to bury or injure a person).

recent observations
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* New snow last night will have been deposited on top of either melt-freeze crust or wet snow on all aspects throughout the forecast area. Graupel was noted at the start of the storm in several locations. At this time there are no weak layers of concern below the old/new snow interface.

* The high sun angle this time of year allows for significant amounts of incoming solar radiation on NW-N-NE aspect terrain that is otherwise well shaded from November through February.

* Snow cover below 7,200' to 7,500' is becoming very thin to nonexistent in many portions of the forecast area. In some locations, snow cover is notably patchy below 8,000'. There area some areas of exception where better snow cover exists at these elevations.

Weather and CURRENT CONDITIONS
weather summary

The bulk of the snowfall with the current storm system fell prior to 1 am last night. Snow showers will be widespread today, especially during the afternoon hours as convection builds. The forecast calls for cloudy skies and below freezing air temperatures today, but sun breaks and rapid warming conditions may occur. Lightning is not expected to occur within the forecast area today, but cannot be ruled out entirely this afternoon. Ridgetop winds continue out of the SW this morning. Wind speeds are on a decreasing trend through this afternoon, but remain strong this morning. Snow showers will end tonight. Short lived high pressure will provide sunny skies on Tuesday. Cloud cover will increase Tuesday night ahead of the next weather system expected to impact the forecast area Wednesday afternoon.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 15 to 20 deg. F.
Max. temperature: 37 to 44 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 55 mph
Maximum ridgetop wind gust: 99 mph
New snowfall: 8 to 13 inches
Total snow depth: 54 to 101 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Cloudy skies with widespread snow showers. Mostly cloudy skies. Scattered snow showers. Sunny skies.
Temperatures: 27 to 33 deg. F. 14 to 19 deg. F. 36 to 42 deg. F.
Mid Slope Winds: SW SW SW
Wind Speed: 10 to 15 mph with gusts to 35 mph. 10 to 15 mph in the evening, becoming light. Gusts to 30 mph. Light winds
Expected snowfall: Likely 2 to 5 in. | Chance up to 2 Likely up to 1 in. | Small chance 1 to 3 0
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Cloudy skies with widespread snow showers. Mostly cloudy skies. Scattered snow showers. Sunny skies.
Temperatures: 21 to 27 deg. F. 12 to 17 deg. F. 30 to 36 deg. F.
Ridge Top Winds: SW W W
Wind Speed: 20 to 30 mph. Gusts to 60 mph in the morning, decreasing to 40 mph in the afternoon. 10 to 15 mph with gusts to 30 mph. 10 to 15 mph with gusts to 25 mph in the morning, becoming light.
Expected snowfall: Likely 2 to 5 in. | Chance up to 2 Likely up to 1 in. | Small chance 1 to 3 0
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