THIS SNOWPACK SUMMARY EXPIRED ON January 22, 2019 @ 7:48 am
Snowpack Summary published on January 20, 2019 @ 7:48 am
Issued by Ryan Lewthwaite -

bottom line:

Seemingly stable riding conditions yesterday does not mean that the snowpack is strong. Todays weather variables of new snow & rain may prompt lingering instabilities to make a resurgence. Previous Wind Slabs could become over saturated with rain creating a Wet Slab issue this afternoon. Looming Deep Slab avalanche potential is still in question, with climax failures sometimes happening with many tracks already upon a slope. The MLK holiday tommorrow could bring fresh snow & an impending avalanche hazard. Virginia Lakes Road has CLOSED.

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.

During the Gale Force winds of our most recent storm, trees suffered the loss of a lot of bark. These destructive winds created very large deposits of snow near & below treeline on aspects facing N-E. With the added new snow & rain today these over loaded slabs could lose strength with the introduction of a traveler. In many areas wind deposits have a soft or wet snow component underneath surface crusts.

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.

Predicted rains today & the unforecasted rains above Sonora Pass on Friday has the slopes retaining some water weight. Barely freezing or not in several Snotel locations has the snowpack in constant motion as a cohesive unit, especially near the surface. The most recent storm slab is still conforming to the slopes, rapid change could cause avalanches in thin or complex snowpack areas, such as Cornices. This problem should dissipate as temperatures drop & lock up moisture in the pack.

Avalanche Character 3: Deep Slab
Deep Slab avalanches are destructive and deadly events that can release months after the weak layer was buried. They are scarce compared to Storm or Wind Slab avalanches. Their cycles include fewer avalanches and occur over a larger region. You can triggered them from well down in the avalanche path, and after dozens of tracks have crossed the slope. Avoid the terrain identified in the forecast and give yourself a wide safety buffer to address the uncertainty.

On Friday we found buried surface hoar 115cm deep within the snowpack on a NE protected 24 degree slope. It took a hard force on a CT to gain collapse, but false test results can occur with this instability. The uncertainty of this deeply buried Persistent Weak Layer keeps it in the forecast. No large human-caused avalanches were reported in the BWRA yesterday, even with active high-marking on precariously steep & loaded slopes. In the unlikely event you do step-down a fracture into this layer the consequences will be catastrophic.

Snowpack Discussion

A breakable surface crust can be found almost everywhere in the BWRA. Although adding some stability, Fridays rain is also contributing water weight to an already fickle snowpack. Firm to unsupportable wind slabs exist on N-E leeward terrain features with soft & moist snow below breakable crusts. In wind & sun protected areas a thin (0.5cm) layer of deeply buried surface hoar can still be found. As deep & isolated as this Persistent Weak layer is, triggering a failure in the slab may be difficult. Although do not rule out the unpredictable nature of these instabilities, finding a thin spot that's connected to the larger slab could propagate fracture across the loaded slope. Wetting rains today could tip the scales of a Wet Slab avalanche in lower elevation steep slopes.

recent observations

-Friday we found evidence that buried surface hoar still exists in isolated areas near treeline. Spitting rain has added a lovely crust to the surface snow. Prior winds have stripped bark from trees & cast snow up large tree trunks.

-Avalanche path "Repeat Offender" released a N-SS-R3-D4-I which deposited trees & debris across Leavitt Lake Road & filled in the creek. Rains likely helped saturate & lubricate the slab causing this avalanche

 

 

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 33 deg. F.
Max. temperature in the last 24 hours: 43 deg. F.
Average wind direction during the last 24 hours: Southwest
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: 58 inches
weather

Friday's saturated atmosphere & yesterday mornings cold temperatures has the BWRA covered in a breakable Melt-Freeze Crust. A fairly warm start to the morning with several Snotel sites reading above freezing. Today we can expect a rain & snow mix below 8000' as a fast blast of moisture hits the Eastern Sierra. Forecast totals are calling for 8-16" in the mountains with an issued Winter Storm Warning until early Monday. This storm will be accompanied by Strong SW winds & a potential for Lightning.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Sunday Sunday Night Monday
Weather: Chance for snow & sporadic lightning Snow Level ~7000' Snow Snow Level Below 7000' Decreasing clouds with a chance for snow Snow Level Below 7000'
Temperatures: 34 to 42 deg. F. 14 to 19 deg. F. 22 to 28 deg. F.
Wind direction: Southwest South becoming Southwest West
Wind speed: 15 to 30 mph increasing to 30 to 40 mph later; gusts to 80 mph 30 to 45 mph; gusts to 80 mph becoming Southwest 20 to 30 mph; gusts to 60 mph late 15 to 25 mph; gusts to 45 mph
Expected snowfall: 2 in. 6 to 10 in. 1 in.
For above 10000 ft.
  Sunday Sunday Night Monday
Weather: Chance for snow & sporadic lightning Snow Level ~7000' Snow Snow Level Below 7000' Decreasing clouds with a chance for snow Snow Level Below 7000'
Temperatures: 26 to 32 deg. F. 8 to 13 deg. F. 13 to 19 deg. F.
Wind direction: Southwest Southwest West shifting to Northwest
Wind speed: 35 to 55 mph; gusts to 80 mph 40 to 60 mph; gusts to 85 mph 25 to 40 mph, gusts to 60 mph shifting to the Northwest 20 to 30 mph; gusts to 45 mph later
Expected snowfall: 2 in. 8 to 12 in. 1 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.