1.5 to 3.5 inches of rain in the last 24 hours combined with an addition 3 to 5 inches of rain forecasted during the day today and another 1-3 inches of rain in some areas tonight will add a huge load to the snowpack. This rain will also weaken the snowpack as it melts the bonds holding the snowpack together. The combination of significant loading, weakening, and rapid warming means that natural and human triggered wet slab avalanches will be very likely to certain today. These avalanches could occur on any aspect, run farther than expected, and could be large and destructive involving most of the snowpack especially in areas where the deep slabs mentioned below exist. Wet slab avalanches can start and run on less steep slopes. In addition to wet slab avalanches, widespread loose wet avalanches should also occur today.
Heavy rain and snow will add a very large amount of weight to the snowpack and make it easier for the facets near the 12/15 rain crust to fail. Natural and human triggered deep slab avalanches due to the failure of this layer are very likely to certain today on W-NW-N-NE-E aspects at all elevations. These avalanches will be large, very deep, and destructive. They could also run much farther than expected.
Deep slabs are unpredictable. Remote triggering with large propagation into any connected terrain remains possible. Ski tracks on a slope will not be an indicator of stability and steep trees will not be a safe zone. Avoiding any terrain where this problem might exist represents the wisest choice for today. Deep slabs can occur on less steep slopes and any slopes steeper than 30 degrees are suspect.
Above snow line where the precipitation falls as snow, strong southwest winds and heavy wet snow will keep adding to the wind slabs that started forming yesterday. Natural and human-triggered large, deep, destructive wind slab avalanches are very likely today on wind loaded slopes. These wind slab avalanches could also step down and become the deep slabs mentioned above.
Freezing levels rose much faster than expected yesterday and rain started falling up to 9000 ft. in some areas by mid-day. Reports of loose wet avalanches occurring around 9:30 am. In the Tamarack Peak area new snow accumulation and strong winds had formed 6-18 inch wind slabs and huge cornices above wind loaded slopes by mid-day. 2 wind slabs that failed during the morning when cornice pieces fell onto the slopes below them were observed along the far east ridge of Tamarack Peak. Hand pits and other observations showed that the heavy new snow was resting on top of a lighter layer of old snow. Ski cuts and kicks on wind loaded test slopes produced limited cracking. Active wind loading continued in this area all day.
|0600 temperature:||31 to 34 deg. F.|
|Max. temperature in the last 24 hours:||34 to 37 deg. F.|
|Average wind direction during the last 24 hours:||Southwest|
|Average wind speed during the last 24 hours:||45 to 55 mph|
|Maximum wind gust in the last 24 hours:||122 mph|
|New snowfall in the last 24 hours:||Snow: 5 to 13 inches | Rain 1 to 3.6 inches|
|Total snow depth:||Along the Sierra Crest: 48 to 71 inches | In the Mt. Rose area: 92 inches|
Snow levels rose more quickly than forecasted during the day yesterday then moved up and down during the day and overnight. Some areas between 8000 and 9000 ft. received 5 to 13 inches of heavy wet snow with some places below 8000 ft. even seeing some snow. However, most of the precipitation below 8000 ft. fell as rain and even in the 8000 to 9000 ft. range much of the precipitation fell as rain. So far about 1.5 to 3.5 inches of water has fallen since yesterday morning. Snow levels should stabilize at between 9000 and 9500 ft. today and more intense heavy rain is expected during the day today. The forecast calls for 3 to 5 inches of rain below 9000 ft. today with 15 to 30 inches of heavy wet snow above 9000 ft. Precipitation should continue tonight but the intensity should start to decrease tonight. Snow levels should also start to fall and rain should change over to mostly snow above 7000 ft. after midnight. The forecast calls for another 1 to 3 inches precip tonight with most of that falling as snow above 8000 ft. (18 to 28 inches) and a mix of rain and snow below 8000 ft. (snow: 4 to 10 in. - rain: 1.5 to 2.5 in). By tomorrow colder temperatures should prevail and snow levels should drop below lake level. Snowfall will continue with the forecast calling for another 6 to 12 inches of new snow during the day tomorrow. Gale force southwest winds should continue through tomorrow with ridgetop gusts in the 90 to 115 mph range and sustained wind speeds in the 45 to 65 mph range.
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