THIS SNOWPACK SUMMARY EXPIRED ON February 7, 2021 @ 8:31 am
Snowpack Summary published on February 5, 2021 @ 8:31 am
Issued by Jason Mozol - Bridgeport Avalanche Center

bottom line:

Reactive wind slabs exist on nearly all aspects and are especially well formed on N-E aspects and in protected, concave terrain from extreme winds on Tues/Wed. If deep slabs are to be triggered it would most likely occur in shallow areas of the snowpack, such as lower elevations, near rocks, near trees or convex rolls, and be large to very large in size.

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.

We observed numerous crowns from avalanches that released during extreme wind Tuesday and Wednesday. These new wind slabs exist alongside older slabs that formed during last week’s storm and may be encountered on nearly any aspect. These wind slabs are reactive to a human trigger and vary in thickness from a few inches to many feet resulting in small to large avalanches.

Avalanche Character 2: 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.

Last week’s storm buried a weak layer of facets on W-N-E aspects deep in the snowpack. Areas where the snowpack is thinner, such as lower elevations, near rocks, near trees or convex rolls are places that are more likely to trigger this problem. The best defense is to stick to low angle slopes below 30 degrees that aren't connected to steeper terrain. If venturing into avalanche terrain, evaluate travel routes carefully and identify locations where the snowpack may be thinner.

 
Snowpack Discussion

After the dump of snow last week and extreme winds this week it appears we are headed for a period of calmer weather. In the aftermath of those events, we are left tracking both a deep slab and a wind slab problem. Small, wet snow avalanches can be expected on sun exposed slopes. 

 

We continue to track the weak layer of facets at the ground that create the deep slab problem. Our concern has been that they may become overloaded through storm snow or wind transported snow and fail. So far, only sporadic evidence has given indications of that being the case as the weak snow has been buried so deep it is challenging to trigger. Still, that layer lurks at the bottom and may be triggered in shallower spots in the snowpack. We are still building an understanding of this layer and more information needs to be gathered about how reactive it is in shallow areas of the snowpack.  

 

Extreme winds blew from the S-SW on Tuesday and Wednesday, scouring ridges and leaving wind slabs on N-E aspects. From previous wind events from other directions, there remains the possibility of encountering wind slabs on other aspects. In a snowpit dug near Leavitt Lake we observed small, 2cm, wind slabs forming on top of feet of wind compacted snow. Typically, sheltered terrain and treed slopes can be utilized to avoid this problem but strong winds have had a weaker but still noticeable effect there too.

 
 
recent observations

Crowns from previous avalanching during last week’s storm and this week’s wind event have been observed throughout the forecast area. 

 

Faceted snow continues to exist below the storm and wind transported snow from throughout the last week.

 

Wind affected snow has been observed throughout the area. This formed wind board and bare ground in scoured areas and drifts and wind slabs in protected, leeward areas.

 
 
CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 36 deg. F.
Max. temperature in the last 24 hours: 39 deg. F.
Average wind direction during the last 24 hours: S
Average wind speed during the last 24 hours: 5 mph
Maximum wind gust in the last 24 hours: 18 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 89 inches
weather

Warmer daytime temperatures will pair with seasonably cooler nights below freezing. Winds will be breezy from the north with gusty conditions in the mountains. Skies will be clear with no precipitation. After the dramatic storm the last week of January and this week’s extreme wind event, a return to stable weather conditions with clear skies and gradual warming is a welcome change.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Friday Friday Night Saturday
Weather: Sunny Clear Suny
Temperatures: 37-45 deg. F. 21-27 deg. F. 40-48 deg. F.
Wind direction: E-NE N-NE NW
Wind speed: 10-20 mph, gusts to 35mph 10-20 mph, gusts to 40mph 15mph, gusts to 30mph
Expected snowfall: 0 in. 0 in. 0 in.
For above 10000 ft.
  Friday Friday Night Saturday
Weather: Sunny Clear Sunny
Temperatures: 31-37 deg. F. 19-25 deg. F. 33-39 deg. F.
Wind direction: N-NE NW NW
Wind speed: 25-40mph, gusting to 70mph 15-30mph gusting to 70mph 15-25mph, gusting to 35
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.