THIS AVALANCHE ADVISORY EXPIRED ON March 22, 2017 @ 6:44 am
Avalanche Advisory published on March 21, 2017 @ 6:44 am
Issued by Brandon Schwartz - Tahoe National Forest

Areas of CONSIDERABLE avalanche danger are expected today at all elevations due to a combination of wind slab, storm slab, loose dry, and loose wet avalanche problems. Dry snow avalanche problems are expected above 7,500' to 8,500' today with wet snow avalanche problems below 7,500' to 8,500'. Dangerous avalanche conditions will exist in the backcountry and areas of instability are expected to form rapidly both above and below treeline.

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.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Gale force SSW to SW winds over ridgetops today will create areas of drifting snow and new wind slab formation in near and above treeline areas. The vast majority of new wind slabs are expected to form on W-NW-N-NE-E-SE aspects today. Isolated wind slabs are possible on S-SW aspects as well. Wind direction with this storm has a more S component than the more typical SW to WSW. As a result, wind loading patterns could differ today from what is typical during most storms. Some specific slopes that are typically wind loaded may experience scouring and some specific slopes that are typically scoured may experience wind loading.

Look for and avoid steep slopes in areas where drifting snow is depositing, slopes below cornice features, and steep slopes with newly formed wind pillows.

 

Avalanche Problem 2: Storm Slab
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High intensity snowfall rates in locations that experience convective snow showers may lead to the formation of unstable storm slabs in wind protected areas near treeline and below treeline on all aspects. Be aware of potential rapid increases in instability in below treeline terrain if rapid new snow accumulation occurs.

Look for snow surface cracking while making fresh tracks either uphill or down. Avoid steep slopes in areas where snow surface cracking is occurring.

Loose dry avalanche activity failing on icy melt freeze crusts at the old/new snow interface is also a possibility today on all aspects in wind protected areas near and below treeline.

Avalanche Problem 3: Loose Wet
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Loose wet avalanche activity is possible today on all aspects in any areas where rain falls on new snow. This may occur following convective snow showers where snow level lowers temporarily by up to 1,000'. As the convective shower tapers off, snow level will rise leading to rain on new snow. Rain on old snow is less likely to lead to loose wet avalanche activity today as recent melt has prepared the older snow to handle rain. That said, isolated loose wet avalanches from rain on old snow are not impossible today.

recent observations

Observation made yesterday on Mount Rose proper (Mount Rose area) and on Waterhouse Peak (Luther Pass area) revealed varying amounts of snow surface refreeze. Upper elevation areas above treeline in the 9,000' to 10,000'+ range had a solid snow surface refreeze that had not melted at all at mid day due to strong S winds. Below that generally good snow surface refreeze had occurred with some areas of poor refreeze observed below 8,000'.

Weather and CURRENT CONDITIONS
weather summary

A storm system is spreading through the forecast area from north to south this morning. Snow levels have ranged from around 7,500' to 8,500' thus far. Snowfall today will be convective driven, leading to short periods of high intensity snowfall. Snow levels are expected to fluctuate today, lowering by up to 1,000' during convective bursts. Thunderstorms associated with the convective atmospheric instability are possible today. New snow accumulation is expected to vary widely around the forecast area today due to the convective showers. Some areas could experience short periods of snowfall rates at 2 to 4 inches per hour while other locations not far away experience only very light snowfall or rain. Shower activity is expected to gradually taper off through Wednesday with snow level lowering to 5,500' to 6,000' tonight. Gale force SSW to SW ridgetop winds today are forecast to gradually decrease tonight through tomorrow.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 33 to 36 deg. F.
Max. temperature in the last 24 hours: 40 to 46 deg. F.
Average wind direction during the last 24 hours: SSW
Average wind speed during the last 24 hours: 47 mph
Maximum wind gust in the last 24 hours: 104 mph
New snowfall in the last 24 hours: 3 to 4 inches
Total snow depth: 117 to 170 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Cloudy skies with rain and snow. Widespread showers in the afternoon. Slight chance of thunderstorms through the day. Mostly cloudy skies, becoming partly cloudy. A chance of showers and thunderstorms in the evening. A chance of snow showers after midnight. Partly cloudy skies, becoming mostly cloudy. A chance of snow showers in the morning. Snow showers likely with a slight chance of thunderstorms in the afternoon.
Temperatures: 32 to 42 deg. F. 24 to 29 deg. F. 30 to 36 deg. F.
Wind Direction: S to SW SW SW
Wind Speed: 15 to 25 mph with gusts to 45 mph. 15 to 25 mph with gusts to 45 mph. 10 to 15 mph with gusts to 25 mph in the morning, becoming light.
Expected snowfall: Likely 1 to 4 inches | Possibly 4 to 8 in. Up to 1 in. Likely up to 2 inches | Possibly 2 to 4 in.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Cloudy skies with rain and snow. Widespread showers in the afternoon. Slight chance of thunderstorms through the day. Mostly cloudy skies, becoming partly cloudy. A chance of snow showers and thunderstorms in the evening. A chance of snow showers after midnight. Partly cloudy skies, becoming mostly cloudy. A chance of snow showers in the morning. Snow showers likely with a slight chance of thunderstorms in the afternoon.
Temperatures: 30 to 36 deg. F. 22 to 28 deg. F. 31 to 39 deg. F.
Wind Direction: S to SW SW SW
Wind Speed: 50 to 70 mph with gusts to 100 mph. 40 to 55 mph with gusts to 85 mph. 35 to 45 mph with gusts to 70 mph, decreasing to 15 to 20 mph with gusts to 30 mph in the afternoon.
Expected snowfall: Likely 4 to 10 inches | Possibly 10 to 16 in. Up to 2 in. Likely up to 2 inches | Possibly 2 to 4 in.
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