THIS SNOWPACK SUMMARY EXPIRED ON February 14, 2021 @ 9:02 am
Snowpack Summary published on February 12, 2021 @ 9:02 am
Issued by Jason Mozol - Bridgeport Avalanche Center

bottom line:

Dangerous avalanche conditions exist in the backcountry today. A foot of new snow overnight combined with strong SW winds created fresh avalanche problems on mid and upper elevation slopes. Large human triggered avalanches are very likely on wind loaded slopes today. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential in the backcountry at the moment. Don’t let today’s sunshine fool you; avoid steep wind loaded slopes today. Continued snowfall and winds tomorrow will keep these large avalanches reactive into the weekend.

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 quick hitting storm last night brought around a foot of new snow and strong SW winds, building fresh wind slabs on NW-N-SE facing slopes at mid and upper elevations. These wind slabs are resting on a variety of weak and slick snow surfaces that they may not bond well to. They are likely to be large and touchy today.  Wind slabs can be identified by their smooth texture and are usually found on downwind terrain features. Cracking and collapsing of the new snow are sure signs of instability. Remember that recent avalanches on similar slopes are the biggest red flag for more avalanches. Avoid steep, wind loaded slopes 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.

Last night’s foot of new snow created storm slabs on slopes protected from the wind. These storm slabs may be less obvious and more difficult to trigger than the wind slabs today, but still could be large enough to bury you. Again, be on the lookout for cracking and collapsing in the new snow. Also be aware of terrain traps and other unfriendly terrain that would increase the consequences of even a small avalanche. If you see signs of instability on steep slopes remember that lower angled slopes will be fun and powdery today too.

Snowpack Discussion

Avalanche conditions have been relatively stable over the last week but with last night’s new snow the danger has risen significantly overnight. Be aware of these rapidly changing conditions. Wind and storm slabs pose a significant hazard today and demand a change in travel behavior. Two small storms lined up for the holiday weekend will keep fresh avalanche problems reactive. Continue to practice conservative decision making through the long weekend.

Our deep persistent slab problem has remained relatively dormant recently and last night’s snow likely won’t be enough to reactivate the problem. That being said, our snowpack still has a poor structure with weak facets buried underneath a thick slab on NW-N-E aspects. Snowpit tests show that it is hard to initiate a failure on the facets, but if you do initiate a failure, it would likely propagate into a large avalanche. Thin areas of the snowpack act as trigger points for deep persistent slab avalanches. In these thin spots the slab is thinner, making it easier to impact the buried facets and initiate a failure. Deep persistent slab avalanches are very hard to predict and deserve respect due to their destructive size. If there are any signs of instability on these deeper layers be sure to take a step way back. 

recent observations

6-13 inches of new snow and SW winds overnight. 

Facets buried ~1m deep are slowly healing and hard to affect but still show poor structure and potential for propagation if a failure is initiated.

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 20 deg. F.
Max. temperature in the last 24 hours: 37 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 30-40 mph
Maximum wind gust in the last 24 hours: 65 mph
New snowfall in the last 24 hours: 13 inches
Total snow depth: 96 inches
weather

The sun is out today but it will be short lived. Another small storm is on tap for tomorrow with 4-8 inches of new snow and strong westerly winds forecasted.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Friday Friday Night Saturday
Weather: Partly cloudy then becoming sunny. Chance of snow through the day. Clear then becoming mostly cloudy. Slight chance of snow after midnight. Mostly cloudy. Snow likely in the morning, then snow in the afternoon.
Temperatures: 33 to 39 deg. F. 20 to 25 deg. F. 25 to 33 deg. F.
Wind direction: West West West
Wind speed: around 15 mph with gusts to 40 mph in the morning becoming light. Light winds becoming west around 15 mph with gusts to 40 mph after midnight. 15 to 30 mph with gusts to 60 mph.
Expected snowfall: up to 2 in. 0 in. 70% probability of 1 to 5 in. 30% probability of 3 to 7 in.
For above 10000 ft.
  Friday Friday Night Saturday
Weather: Partly cloudy then becoming sunny. Chance of snow through the day. Clear then becoming mostly cloudy. Slight chance of snow after midnight. Mostly cloudy. Snow likely in the morning, then snow in the afternoon.
Temperatures: 26 to 34 deg. F. 14 to 19 deg. F. 18 to 26 deg. F.
Wind direction: Northwest West West
Wind speed: 15 to 25 mph. Gusts up to 55 mph decreasing to 30 mph in the afternoon. 15 to 25 mph. Gusts up to 40 mph increasing to 50 mph after midnight. 35 to 55 mph with gusts to 85 mph.
Expected snowfall: up to 2 in. 0 in. 80% probability of 1 to 5 in. 20% probability of 3 to 7 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.