THIS AVALANCHE ADVISORY EXPIRED ON January 6, 2018 @ 7:01 am
Avalanche Advisory published on January 5, 2018 @ 7:01 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger is increasing towards CONSIDERABLE avalanche danger at all elevations as rain and wet snow continue. Loose wet, persistent slab, and wind slab avalanche problems are a concern over the next 24 hours.

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: Loose Wet
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Loose wet avalanche activity was reported yesterday and will continue to be a problem with additional rain and wet snow accumulation. Snow covered NW-N-NE aspects at any elevation are the likely location for this avalanche problem to occur. Loose wet avalanches are possible in isolated areas on all other aspects. Avalanche size up to D2 is possible.

Avalanche Problem 2: Persistent Slab
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Rain and wet snow continue to add load to areas of slab over weak faceted snow on NW-N-NE aspects both above and below treeline. Above treeline areas have hard slabs while near to below treeline areas hold soft slabs. Recent field observations have regularly indicated isolated areas of persistent slab instability. A race is on to see if loading brings the facets to a point of failure before increasing moisture from rain and wet snow affects the moisture content and changes the characteristics of the facet layer.

Quick hand pits will remain effective for identifying slab over weak, loose grain (sugary) faceted snow until significant new snowfall occurs. Keep in mind that this problem exists in isolated areas so investigate the snowpack structure frequently as you cover terrain. This problem may exist only in the mid to lower portion of avalanche start zones. Avoid steeper slopes in areas where snow surface cracking, whumpfing, and/or unstable snowpit test results are occurring. Small avalanches can have increased consequences right now given the prevalence of rocks and trees.

Avalanche Problem 3: Wind Slab
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Development of a wind slab avalanche problem tonight will be directly related to snow level and new snow accumulation. If snow levels are at the lower end of forecast elevation and snowfall amounts push the upper end of forecast possibility, wind slabs will form tonight. Near and above treeline areas on NW-N-NE-E aspects above 8,000' will be most problematic.

Look for and avoid areas of drifting snow, especially along ridgelines where cornices and/or wind pillows have formed.

recent observations

* Loose wet avalanche activity occurred yesterday in the Mount Rose area on steep northerly aspect terrain in the 8,600' to 9,200' elevation range. Avalanche size was large enough to injure a person.

* The recent rain, wet snow, and high humidity has added significant moisture to areas that held faceted snow on the surface with no overlying slab. Where faceted snow exists under a slab, the facets have thus far remained dry.

* Observations from around the forecast area this past week have shown isolated areas of unstable persistent slabs (slab over faceted snow) on NW-N-NE aspects, especially near and below treeline.

* NW-N-NE aspects above 8,000' in the Mt. Rose area and along the Sierra Crest north of Emerald Bay hold the best snow coverage at 2 to 3+ feet. Overall less snow cover exists south of Emerald Bay. Areas of decent coverage exists above 8,500' on NW-N-NE aspects in the Carson Pass area.  Coverage decreases on all other aspects. Large areas of bare ground exist on the vast majority of southerly aspects at all elevations.

Weather and CURRENT CONDITIONS
weather summary

Rain and snow showers last night brought another 0.1 to 0.4 inches of rain to most locations within the forecast area. A few of the upper elevation locations above 8,500' picked up 1 to 2 inches of new snow. Light rain and snow showers are expected today with snow level around 8,000'. A more potent weather system is forecast to pass through the region tonight. Snow levels will remain around 8,000', possibly lowering to 7,000' during any periods of higher intensity precipitation. Rainfall amounts tonight are expected to reach 0.75 to 1.0 inches. Snowfall amounts are uncertain with significant accumulations potentially limited to areas above 8,500'. The elevation that snow level ultimately ends up occurring will have a significant effect on the outcome. Rain and snow showers are expected to linger through Saturday. Ridgetop winds will be out of the S to SW today and tomorrow. Moderate to strong wind speeds are expected with peak speeds occurring tonight or tomorrow morning. A more powerful storm system is lining up to impacted the forecast area Mon/Tues.

 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 30 to 36 deg. F.
Max. temperature in the last 24 hours: 34 to 42 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 41 mph
Maximum wind gust in the last 24 hours: 76 mph
New snowfall in the last 24 hours: Snow 1 to 2 | Rain 0.1 to 0.4 inches
Total snow depth: 18 to 33 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy skies. Scattered rain and snow showers. Snow level 8,000'. Mostly cloudy skies. Scattered rain and snow showers in the evening. Widespread showers after midnight. Snow level 7,000' to 8,000'. Mostly cloudy skies. Scattered rain and snow showers in the morning. A chance of showers in the afternoon. Snow level 7,000' to 8,000'
Temperatures: 43 to 49 deg. F. 31 to 36 deg. F. 39 to 44 deg. F.
Wind Direction: S S SW
Wind Speed: 15 to 20 mph with gusts to 40 mph. 20 to 30 mph. Gusts to 45 mph increasing to 60 mph after midnight. 15 to 25 mph. Gusts up to 60 mph, decreasing to 40 mph in the afternoon.
Expected snowfall: 0 to 1 in. Likely 1 to 2 in.| Small chance 3 to 4 in. Likely up to 1 in. | Small chance 2 to 3 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy skies. Scattered rain and snow showers. Snow level 8,000'. Mostly cloudy skies. Scattered snow showers in the evening. Widespread showers after midnight. Snow level 7,000' to 8,000'. Mostly cloudy skies. Scattered snow showers in the morning. A chance of showers in the afternoon. Snow level 7,000' to 8,000'
Temperatures: 37 to 43 deg. F. 29 to 34 deg. F. 35 to 40 deg. F.
Wind Direction: S S SW
Wind Speed: 25 to 40 mph with gusts to 70 mph. 30 to 50 mph. Gusts to 70 mph increasing to 80 mph after midnight. 30 to 45 mph with gusts to 85 mph, decreasing to 25 to 35 mph with gusts to 65 mph in the afternoon.
Expected snowfall: Likely up to 1 in. | Small chance 2 to 3 in. Likely 1 to 5 in. Possible 6 to 10 in. Likely up to 2 in. | Possible 3 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