THIS AVALANCHE FORECAST EXPIRED ON March 13, 2018 @ 6:57 am
Avalanche Forecast published on March 12, 2018 @ 6:57 am
Issued by Brandon Schwartz - Tahoe National Forest

Avalanche danger is LOW for all elevations. Small loose wet avalanches may occur today. Deep slab avalanches are very unlikely but not impossible on a regional scale.

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Loose Wet
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    Certain
    Very Likely
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Air temperatures at 0600 this morning at the upper elevations are 6 to 8 degrees warmer than 24 hours ago and are above freezing. Clear skies and radiational cooling last night are expected to have allowed for some overnight snow surface refreeze despite above freezing air temperatures. The warmer sunny start to this morning, forecast daytime air temperatures above 7,000' well into the 40s, and the possibility of evening rain will combine to increase the likelihood of loose wet avalanche problems today into tonight. Avalanche size is expected to be small and could occur on any aspect.

Look for fresh roller ball activity as a sign of instability. If in doubt avoid steep slopes where any signs of wet snow instability, either new or old are present.

Avalanche Problem 2: Normal Caution
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Triggering a deep slab avalanche is very unlikely on a regional scale but cannot be ruled out entirely. Most snowpack data points to significant improvements in stability over the past week, but a few outliers exist. Keep in mind that in the unlikely event that a deep slab avalanche is triggered, avalanche size will be large (up to D3). Factor large avalanche size into travel plans and route selection on NW-N-NE-ENE aspects. If in doubt, increase the margin of safety by choosing less complex terrain and increasing the distance from areas of exposure to potential avalanches.

The main focus of the lingering deep slab issue is not so much on an avalanche occurring today, but on monitoring of the layer of concern to determine how it may respond to new snow loading by the series of storms forecast for the remainder of this week.

recent observations
Submit Observations

* Sun and warming have continued to affect the snow surface in most areas, including many N aspects below about 8,500'.

* Observations made yesterday on Elephants Hump (Carson Pass area) on a previously fractured and investigated slope showed a significant stability increase of the faceted weak layer associated with the recent deep slab problem.

* Observations received yesterday from Powderhouse Peak (Luther Pass area) pointed to isolated, lingering instability of the deep slab problem.

* Other observations over the past week from around the forecast area targeting the recent deep slab problem have overall shown signs of increasing stability. Outliers continue to present, most recently from the Luther Pass and Echo Summit areas. General trends in snowpit data are that the once faceted weak layer of concern is located 3 to 6 feet deep in the snowpack on NW-N-NE-ENE aspects, remains significantly less dense than the slab above it, and often presents as loose grains. Varying degrees of rounding of the once faceted snow have be observed. In some locations, faceted crystals are no longer visible under magnification. In other locations, striated faceted crystals remain. Snowpit tests mostly indicate that it is difficult to trigger weak layer failure (ECT, CT). There are some exceptions. Tests specifically examining propagation potential (such as the PST) tend to indicate that propagation could still occur along the weak layer in the unlikely event that snowpack failure is triggered.

Weather and CURRENT CONDITIONS
weather summary

The forecast calls for a mild day today with generally sunny skies, above freezing air temperatures, and increasing S winds. This is ahead of a series of approaching storm systems that will bring rain and snow to the forecast area starting tonight. Increasing snowfall intensity and lowering snow levels are expected Tuesday afternoon/evening. Ridgetop winds are forecast to increase to strong to gale force out of the SW tomorrow.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 33 to 36 deg. F.
Max. temperature: 45 to 49 deg. F.
Average ridgetop wind direction: S
Average ridgetop wind speed: 8 mph
Maximum ridgetop wind gust: 37 mph
New snowfall: 0 inches
Total snow depth: 46 to 80 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy skies, becoming sunny. Partly cloudy skies, becoming cloudy. A chance of rain through the night. Snow level 8,500'. Cloudy skies. A chance of rain and snow. Snow level 8,000' lowering to 7,000' in the afternoon.
Temperatures: 45 to 50 deg. F. 32 to 37 deg. F. 39 to 44 deg. F.
Mid Slope Winds: S SW S
Wind Speed: Light winds 10 to 20 mph. Gusts to 35 mph increasing to 50 mph after midnight. 20 to 30 mph with gusts to 55 mph.
Expected snowfall: 0 Rain less than 0.1 Up to 5
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy skies, becoming sunny. Partly cloudy skies, becoming cloudy. A chance of rain and snow through the night. Snow level 8,500'. Cloudy skies. A chance of rain and snow. Snow level 8,000' lowering to 7,000' in the afternoon.
Temperatures: 41 to 47 deg. F. 30 to 35 deg. F. 35 to 41 deg. F.
Ridge Top Winds: S SW S
Wind Speed: 15 to 20 mph with gusts to 40 mph. 15 to 25 mph with gusts to 55 mph, increasing to 25 to 40 mph with gusts to 85 mph after midnight. 30 to 45 mph with gusts to 95 mph.
Expected snowfall: 0 Trace to 1 2 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