THIS SNOWPACK SUMMARY EXPIRED ON January 14, 2019 @ 7:49 am
Snowpack Summary published on January 12, 2019 @ 7:49 am
Issued by Ryan Lewthwaite -

bottom line:

Soft snow is readily available for riding enjoyment in the Bridgeport Winter Recreation Areas. Use caution while traveling on N-E slopes that look convex or pillowy due to a persistent slab problem. This avalanche issue can be found near & below treeline on isolated features that exhibit loading from last weeks storms. Not showing straight-forward stability results can allow you to assume the problem still lingers with the potential for large sized avalanches. Use a slope meter to keep yourself from getting too step, avalanches can occur on slopes less than 35 degrees.

Avalanche Character 1: Persistent Slab
Persistent Slab avalanches can be triggered days to weeks after the last storm. They often propagate across and beyond terrain features that would otherwise confine Wind and Storm Slab avalanches. In some cases they can be triggered remotely, from low-angle terrain or adjacent slopes. Give yourself a wide safety buffer to address the uncertainty.

Isolated features on aspects N-E near & below treeline have been surprising backcountry travelers with reactive slab failure. The avalanches have been releasing on a similar layer within the snowpack, using the old snow surface that existed prior to last weekends storms. Variable thickness & distribution of snow atop this layer & the stubbornness to get collapse can become a problem for identifying where this issue resides. A snowmobile triggered soft slab avalanche occured Wednesday in the confluence of Leavitt & Ski Lake drainages, no injuries.

Snowpack Discussion

We have gained roughly 2.5' of snow since the arrival of storms last weekend. The overall stability of the snowpack is good, although isolated persistent slabs still linger on N-E aspects near & below treeline. Fairly similar avalanches across the E Sierra have been recognized to fail at the old snow/ new snow interface which holds faceted grains. This type of avalanche may be difficult to propagate but it has the potential to go big, up to a destructive force of 3 (ability to ruin a car, house, or train). An avalanche investigation yesterday showed tracks on the slopes prior to collapse, & it took 4 high-marks before the failure occured. SS-AM-R2-D2-I Soft slab avalanche, triggered by a snowmobile, Range of 2, Destructive potential of 2, failing at old snow/ new snow interface. The rider initiated the crack at a slope angle of 34 to an angle 38, propagating between trees & rocks with a crown of 2'. I found chains of depth hoar within cavities in & around this event. 

recent observations

Snowpack & Avalanche observations this week have been plentiful, even obtaining public input & photos of a snowmobile triggered slide. Other obs evaluate the recent snows from last weekend & the quick Wednesday night precip. Our "stormboards" have been recording the new snow amounts all the way down to our trailhead.

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 16 deg. F.
Max. temperature in the last 24 hours: 37 deg. F.
Average wind direction during the last 24 hours: South
Average wind speed during the last 24 hours: light mph
Maximum wind gust in the last 24 hours: moderate mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 41 inches
weather

Cloudy today with average seasonal temperatures. Winds will be light through the weekend, coming out of the South & Southeast. No new precipitation until Monday morning, then a large storm develops mid-week. Models show strong support for a blizzrd-like winter storm Tues-Thurs with "feet" of snow for even low elevations.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Saturday Saturday Night Sunday
Weather: Mostly cloudy Snow Level Below 7000' Clear Snow Level Below 7000' Sunny Snow Level Below 7000'
Temperatures: 30 to 36 deg. F. 12 to 18 deg. F. 29 to 35 deg. F.
Wind direction: Southeast to South Southeast to South Southeast
Wind speed: 10 to 15 mph; gusts to 25 mph 10 to 15 mph 10 to 15 mph; gusts to 30 mph
Expected snowfall: 0 in. 0 in. 0 in.
For above 10000 ft.
  Saturday Saturday Night Sunday
Weather: Mostly cloudy Snow Level Below 7000' Clear Snow Level Below 7000' Sunny Snow Level Below 7000'
Temperatures: 23 to 28 deg. F. 6 to 12 deg. F. 22 to 28 deg. F.
Wind direction: East to Southeast East Southeast
Wind speed: 10 to 20 mph; gusts to 30 mph 15 to 25 mph 15 to 25 mph; gusts to 35 mph
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer

This snowpack summary applies only to backcountry areas in the Bridgeport Winter Recreation Area. Click here for a map of the area. This snowpack summary describes general avalanche conditions and local variations always occur. This snowpack summary expires in 48 hours unless otherwise noted. The information in this snowpack summary is provided by the USDA Forest Service who is solely responsible for its content.