THIS SNOWPACK SUMMARY EXPIRED ON February 5, 2021 @ 9:41 am
Snowpack Summary published on February 2, 2021 @ 9:41 am
Issued by Jason Mozol - Bridgeport Avalanche Center

bottom line:

Dangerous avalanche conditions exist. Human triggered avalanches are likely, while natural avalanches are possible. New snow and strong winds will create a need for backcountry travelers to practice good route-finding decisions. Avoid areas where wind drifted snow has collected. A weak layer may be present in isolated locations on W-N-E aspects, thoughtful snowpack evaluation is essential to help navigate the deep persistent slab problem.

 

The Bridgeport Winter Recreation Area (BWRA) on the Humboldt-Toiyabe National Forest's Bridgeport Ranger District is now open for snowmobiling. Highway 395 remains closed between Walker and Sonora Junction as CalTrans continues to remove avalanche debris from Walker Canyon.

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.

Up to 10” of new snow and extreme SW winds of 50-80mph will be the driving factors creating the wind slab hazard today. Wind slabs will be found on N-NE-E slopes. Avoid areas where smooth wind pillows have formed, such as convex slopes, under ridge tops or areas where snow has collected. Wind slabs can remain reactive days after the initial storm. Be observant of the aspect you are on and signs of instability. Use thoughtful terrain choices to help manage risk today.

Avalanche Character 2: 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.

If the higher end of the forecasted snowfall totals occur, a storm slab avalanche problem will present itself. With 10” of incoming snow and high winds, storm slabs will be found in isolated areas. High winds will scour and deposit snow on lee aspects. In sheltered areas, snow may exist that is not affected by high winds. It is likely that if you enter sheltered terrain you will find storm slabs that will avalanche under a human trigger.

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.

Prior to the Jan 26th storm, the snowpack was shallow and had a significant layer of weak snow at the bottom of the snowpack. The epic storm last week dropped six feet of snow on this weak snow. While this weak layer is buried under a huge slab of storm snow, the weak snow could reactivate if the right amount of stress is applied in the right place such as a convex shaped slope or a thinner area of the slab. We know this layer exists- what we don’t know is what it would take to cause an avalanche to release. What we do know is if an avalanche releases, it could release a very large amount of snow that could easily kill a person or bury a sled. To avoid this problem, stay off of slopes steeper than 30 degrees on W-N-E aspects.

 

 
Snowpack Discussion

Deep snow conditions have limited our ability to gain access to avalanche terrain in the BWRA. This has created uncertainty around weak layers within the snowpack.  Cloud cover has kept warm air in the mountains overnight. Sonora Pass snotel recorded a low of only 32F last night at 8770ft. Solar input has been limited by cloud cover and recent loading may further affect the weak stability. Caution is advised when dealing with a deep persistent slab, it may not avalanche, but if it does outcomes may be dire. Very large avalanches have very large consequences.

If the higher end of the forecast rings true, 10 inches of new snow will be added to the snowpack. Strong wind will either scour slopes, or load them with even more snow depending on aspect.  Isolated areas of sheltered terrain may avoid wind effect and develop storm slabs. Wind can move snow so efficiently you may find places 3 to 5x deeper than projected snowfall totals. Be mindful of changing surface conditions, if you find yourself on a slope that is deeper than surrounding areas, you are most likely on a wind slab.

 

Help the BAC avalanche forecast! Submit your observations.

 

Join us for a FREE avalanche awareness class this Fri-Sat. More information can be found at, https://www.bridgeportavalanchecenter.org/avalanche-awareness-class

 

 

recent observations
  • Twin Lakes road was covered by avalanche debris after a mid storm avalanche. The avalanche was on a SW aspect, and the path was over 1000ft long

  • Wind transport was visible on Crater Crest and Monument Ridge.(2.1.21)

  • Northerly aspects below ridgelines in the MT Emma area showed evidence of storm cycle avalanches

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 32 deg. F.
Max. temperature in the last 24 hours: 40 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 55 mph
Maximum wind gust in the last 24 hours: 76 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 55 inches
weather

Beginning today, a moderate storm system will bring snowfall and strong winds. Between 6-10 in.  of snow is forecasted for the mountains. New snow will be accompanied by 50 mph winds and gusts up to 80 mph. The storm will slowly begin Tuesday, reach peak intensity Tuesday night and tapper of Wednesday. This storm is forecasted to be much warmer than the last system that came through. Today's high in the mountains is 31F, this will result in a much denser, heavier snow.

 
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Tuesday Tuesday Night Wednesday
Weather: Partly cloudy. Chance of snow in the afternoon. Mostly cloudy. Chance of snow through the night. Partly cloudy. Slight chance of snow through the day.
Temperatures: 30 to 38. deg. F. 16 to 21. deg. F. 22 to 30. deg. F.
Wind direction: SW SW SW
Wind speed: 20 to 30 mph with gusts to 60 mph. 15 to 30 mph with gusts to 50 mph. 15 to 30 mph with gusts to 50 mph.
Expected snowfall: 80% probability of up to 2 inches. in. 70% probability of 3 to 7 inches. in. 70% probability up to 1 inch. in.
For above 10000 ft.
  Tuesday Tuesday Night Wednesday
Weather: Partly cloudy. Chance of snow in the afternoon. Mostly cloudy. Chance of snow. Mostly cloudy then becoming partly cloudy. Chance of snow through the day.
Temperatures: 22 to 30. deg. F. 11 to 16. deg. F. 15 to 23. deg. F.
Wind direction: SW SW SW
Wind speed: 40 to 60 mph decreasing to 30 to 50 mph 30 to 45 mph with gusts to 70 mph. 35 to 55 mph decreasing to 30 to 45 mph in the afternoon. Gusts up to 85 mph.
Expected snowfall: 80% probability up to 2 inches. in. 70% probability of 3 to 7 inches. in. 70% probability up to 1 inch. 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.