Issued by Brandon Schwartz - Tahoe National ForesthT_h
A break in cloud cover will occur today and tomorrow for a few days of sunshine in between weather systems. A cold front passing to the NE of the forecast area today will keep strong SW winds ongoing over the ridgetops today. Maximum daytime air temperatures will warm above freezing today for nearly all locations with strong incoming solar radiation. Ridgetop winds will begin to decrease tonight. A shift to E winds is expected tomorrow morning with moderate speed gusts on the ridgetops. More storm systems are expected to bring snowfall to the forecast area this weekend.
* Yesterday on Lincoln Ridge (Yuba Pass area), a wind slab avalanche with a 1 foot crown was intentionally triggered by cornice collapse on a NE aspect in near treeline terrain. A crack across the bed surface went another 2 feet down to snowpack failure on the buried surface hoar layer that is a part of the persistent slab avalanche problem. Snowpit tests performed earlier in the tour had identified unstable conditions on the 10 mm+ gain size surface hoar layer 1 foot below the snow surface in wind protected areas.
* Fog, mist, and low elevation very light rain yesterday morning created very moist snow surface conditions up to at least 8,000' (and possibly much higher) on all aspects. Wet surface snow was widespread below 7,200'.
Unstable wind slabs existed yesterday and are expected again today. Strong SW ridgetop winds have scoured most all snow on the ridgetops available for transport and created wind slabs where this drifting snow has deposited in lee areas. Areas of unstable wind slabs formed in lee areas exist above treeline and near treeline on NW-N-NE-E-SE aspects. Avalanche size is expected at D1 to D2.
Leeward slopes below ridgetops adjacent to wind scoured areas, slopes below cornice formations, and slopes with new wind pillows are all indications of where unstable wind slabs may be encountered. Identify the areas of concern and move around them with caution. These wind slabs are dense and have increased destructive potential for their size, with smaller avalanches having increased potential for creating injury. These wind slabs may be stubborn and not respond to the first trigger.
This avalanche problem has become a somewhat nasty lurker. Unstable snowpack conditions on a weak layer of buried surface hoar are clearly ongoing on isolated slopes around the forecast area. Spatial variability is at play here with weak layer stabilization occurring at different rates in different locations. Isolated persistent slab avalanches failing 1 to 3 feet deep in the snowpack may occur in areas without signs of current instability and with numerous previous tracks. NW-N-NE aspects at all elevations remain suspect. Avalanche size is expected at D2 and the high density of the slab could easily create injury.
With the variability and isolated distribution, it would be very easy to travel around all day without noticing any indications of instability right up until triggering an avalanche. Avoiding NW-N-NE aspects or using only slopes of less than 30 degrees in slope angle, not connected to steeper slopes above or to the side are the true tools for avoiding this avalanche problem. Heavily treed terrain should be without this avalanche problem, but any open areas within this heavily treed terrain are highly suspect.
High sun angles and strong incoming solar radiation will create snow surface warming on all aspects today including N. Rollerballs and loose wet avalanches are expected today in wind protected areas on all aspects, especially around exposed rocks. Avalanche size is expected at D1 with an isolated D2 not impossible.
With fairly clear skies this morning and fairly warm air temperatures last night this avalanche problem is expected to form quickly today. With size D1 avalanches, consequences will come from being pushed into or over downslope terrain features such as rocks, trees, cliffs, and terrain traps. These terrain features could make high consequences from an otherwise small avalanche. Rollerballs and pinwheels are indications that this avalanche problem is present.
|0600 temperature:||23 to 28 deg. F.|
|Max. temperature in the last 24 hours:||31 to 34 deg. F.|
|Average wind direction during the last 24 hours:||SW|
|Average wind speed during the last 24 hours:||49 mph|
|Maximum wind gust in the last 24 hours:||75 mph|
|New snowfall in the last 24 hours:||inches|
|Total snow depth:||58 to 79 inches|
This avalanche forecast is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This forecast 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 forecast applies only to backcountry areas outside established ski area boundaries. This forecast describes general avalanche conditions and local variations always occur. This forecast expires 24 hours after the posted time unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.
For a recorded version of the avalanche forecast call (530) 587-3558 x258
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