THIS AVALANCHE FORECAST EXPIRED ON April 16, 2018 @ 6:48 am
Avalanche Forecast published on April 15, 2018 @ 6:48 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger will exist for most of today at all elevations due to a loose wet avalanche problem. As new snowfall and wind impact the forecast area this evening, avalanche danger will increase to CONSIDERABLE danger near treeline and above treeline due to a wind slab avalanche problem.

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: Loose Wet
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SW winds mixed out air temperature inversion conditions last night allowing for air temperatures to fall below freezing above 8,500'. Snow surface refreeze contributions from radiational cooling were compromised by periods of cloud cover last night. As a result, a weak to decent snow surface refreeze is expected to have occurred last night. Surface refreeze was likely a little better above 9,000'. Periods of sunshine this morning and above freezing air temperatures will create snow surface melt that leads to another round of loose wet avalanche problems. Loose wet avalanches will be possible today on all aspects at all elevations. Avalanche size up to D2 is possible (large enough to bury or injure a person). Increasing cloud cover will temper afternoon melt rates, but sufficient melt is expected this morning to get this avalanche problem going.

Mid and upper elevation NW-N-NE aspects may see human triggered roller balls as an indication of potential unstable conditions as the recent storm snow continues to transition to corn. Where melt-freeze conditions are well established on E-SE-S-SW-W aspects, focus on monitoring snow surface supportability. Once the snow surface is in melt phase and conditions become marginally supportable to unsupportable, avoid travel in or below avalanche terrain.

Avalanche Problem 2: Wind Slab
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Following the onset of snowfall, a wind slab avalanche problem will develop this evening near 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). Identify areas of wind drifted snow near ridgelines and in gully features. Avoid avalanche terrain in areas where snow surface cracking is occurring. Slopes with cornice features or wind pillows across the upper portion of the slope will become highly suspect.

recent observations
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* Observations were made yesterday on Stevens Peak (Carson Pass Area). Warming conditions and snow surface melt were observed in this area on all aspects. Recent storm snow on E-SE-S-SW-W aspects was assimilated with the older melt-freeze snow below it up to the highpoint of travel around 9,800'. An intentionally skier triggered loose wet avalanche occurred at noon on a NE aspect at 8,800' where the recent storm snow was entering into melt phase for the first time.

* The high sun angle this time of year is allowing 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'.

Weather and CURRENT CONDITIONS
weather summary

An approaching storm system will bring strong SW winds and increasing cloud cover to the forecast area today. Precipitation is expected to begin in the late afternoon to evening time frame. Snow levels are forecast to start out around 7,500' this afternoon, quickly falling below 5,000' this evening. The period of highest intensity snowfall across the forecast area is expected this evening between 6 pm and 11 pm. Residual snow showers will last through Monday. Short lived high pressure is forecast for Tuesday.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 31 to 36 deg. F.
Max. temperature: 46 to 51 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 31 mph
Maximum ridgetop wind gust: 50 mph
New snowfall: 0 inches
Total snow depth: 48 to 88 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy skies. A chance of rain and snow in the afternoon. Snow level 7,500'. Cloudy skies with snow. Mostly cloudy skies. Snow showers likely in the morning. Widespread snow showers in the afternoon.
Temperatures: 44 to 50 deg. F. 19 to 24 deg. F. 28 to 33 deg. F.
Mid Slope Winds: SW SW SW
Wind Speed: 15 to 25 mph with gusts to 45 mph, increasing to 25 to 35 mph with gusts to 60 mph in the afternoon. 20 to 35 mph with gusts to 70 mph, decreasing to 15 to 25 mph with gusts to 60 mph after midnight. 10 to 15 mph with gusts to 35 mph.
Expected snowfall: Trace to 1 Likely 4 to 8 in. | Small chance 8 to 12 Likely 1 to 4 in. | Small chance 4 to 6
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy skies. A chance of snow in the afternoon. Cloudy skies with snow. Mostly cloudy skies. Snow showers likely in the morning. Widespread snow showers in the afternoon.
Temperatures: 39 to 45 deg. F. 15 to 20 deg. F. 22 to 28 deg. F.
Ridge Top Winds: SW SW SW
Wind Speed: 25 to 35 mph with gusts to 70 mph, increasing to 30 to 50 mph with gusts to 80 mph in the afternoon. 35 to 55 mph decreasing to 30 to 45 mph after midnight. Gusts up to 90 mph. 20 to 30 mph. Gusts up to 60 mph decreasing to 40 mph in the afternoon.
Expected snowfall: Up to 1 Likely 5 to 10 in. | Small chance 10 to 14 Likely 1 to 4 in. | Small chance 4 to 6
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