THIS SNOWPACK SUMMARY EXPIRED ON February 15, 2019 @ 7:40 am
Snowpack Summary published on February 13, 2019 @ 7:40 am
Issued by Ryan Lewthwaite -

bottom line:

A volitile set of conditions exist in the BWRA today. Another Atmospheric River event has inundated our mountains & will persist with a mix of Rain, Snow & damaging Winds. Avalanche Danger will be High for several days & travel in Avalanche Terrain is not recommended. Travel in general should be avoided around the Sierra Crest as these conditions call for Gale SW winds, prolonged periods of Rain & possibly low elevation Ice. Be alert for falling snow, breaking trees, roof avalanches & of course overall BIG mountainous avalanches.

Avalanche Character 1: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

A look outside yesterday told the story of uninhibited winds that were scouring the mountains. Gale Southwest winds blew dry snow from the most recent storm to deposits on aspects which face NW-N-E-SE. Snowy tornadoes were visible at various points throughout the day & a gust was recorded to be 127 mph!

Avalanche Character 2: Wet Slab
Wet Slab avalanches occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoid avalanche terrain when you see pinwheels, roller balls, loose wet avalanches, or during rain-on-snow events.

A mix of Rain on Snow is occuring this morning at elevations below 8500'. The snowpack is over a meter deep in this elevation band and suspect to failing with regards to shear strength. Rain weight in the snowpack presents complications when it is introduced rapidly & for prolonged periods. Avoid being on or under slopes which exhibit a wet slushy consistency.

Avalanche Character 3: Storm Slab
Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.

This storm is trying to squeeze out its abundance of moisture on us. Whatever its form of precipitation the developing Storm Slab will be dense & not stable on steep slopes. Confidence with storm totals is wavering but expect over 2 feet of wet snow through tomorrow.

Snowpack Discussion

Cold dry powder has been tossed about & turned to slush by rain & wind yesterday through this morning. Unnecessary high winds yesterday has scallopped the alpine & into treeline areas, leaving behind windpack or bare ground. The below treeline zone is buff with wind deposits, on aspects NW-N-E-SE, that could show high reactivity to triggering by natural or human influences. Rain on snow from elevations of 8500' to below 7000' will be a High Danger area for travelers due to Wet Slab instabilities.

recent observations

~Very Strong W/SW winds yesterday were able to transport any loose dry snow. Spin-drifts or snow vortices were seen on higher elevation ridges. Wind eroded snow was sublimating in the sun. Falling snow from trees was causing small Loose Dry avalanches.

~Smaller size Wind Slab & Cornice avalanches were observed in the alpine yesterday.

~Soft powder conditionswere found below treeline. Large pillows in lower elevation areas 

~Be concerned about the weight of Rain on Snow in the mountains & on your roof. (RIP Jeff Nissman)

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 31 deg. F.
Max. temperature in the last 24 hours: 34 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: Strong mph
Maximum wind gust in the last 24 hours: Gale mph
New snowfall in the last 24 hours: +/-(2) inches
Total snow depth: 93 inches
weather

Welp, we are enduring a pretty amazing (AR) Atmospheric River weather event. As described in the name, a less cold moisture rich plume of vapor is slamming into the mountains of the Sierra. Starting near the equator, this violent storm system carries with it strong winds, lightning & less-predictable weather. An unusually strong wind phenomenon called a "sting jet" has been noted in weather models, equalling severe damaging winds. The mixing zone of snow & rain will be between 7000' & 8500' today. Take into account there is a lot of snow in this below treeline zone & the potential is there for large sized Wet Slab avalanches with the addition of rain weight. Dry snow is capable of holding substantial water weight before it fails in shear strength.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Cloudy with a mix of snow & rain. Afternoon rain. Snow Level Below 7000' increasing to 8000' in the afternoon. Cloudy with a mix of snow & rain. Snow Level 8500' Cloudy with a mix of rain & snow. Afternoon snow. Snow Level 8500' decreasing to 7000' in the afternoon.
Temperatures: 35 to 43 deg. F. 29 to 34 deg. F. 33 to 41 deg. F.
Wind direction: Southwest Southwest South
Wind speed: 30 to 45 mph; gusts to 100 mph! 30 to 45 mph; gusts to 90 mph! 30 to 50 mph; gusts to 85 mph!
Expected snowfall: 8 to 16 in. 7 to 14 in. 8 to 16 in.
For above 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Cloudy with snow. Snow Level 7000' increasing to 8000' in the afternoon. Cloudy with snow. Snow Level 8500' Cloudy with snow. Snow Level 8500' decreasing to 7000' in the afternoon.
Temperatures: 28 to 34 deg. F. 24 to 29 deg. F. 26 to 31 deg. F.
Wind direction: Southwest Southwest Southwest
Wind speed: 75 to 95 mph; gusts to 145 mph! 80 to 110 mph; gusts to 155 mph! 55 to 75 mph; gusts 145 mph!
Expected snowfall: 12 to 20 in. 10 to 18 in. 12 to 20 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.