THIS SNOWPACK SUMMARY EXPIRED ON January 27, 2021 @ 8:56 am
Snowpack Summary published on January 26, 2021 @ 8:56 am
Issued by Jason Mozol - Bridgeport Avalanche Center

bottom line:

 Yesterday’s fresh snow and moderate wind have created wind slabs in isolated terrain. Evaluate snowpack and terrain cautiously, be mindful of sheltered areas that have collected wind transported snow. Fresh wind slab development will continue through today, even with the break in snow. A human triggered avalanche today is possible, it may not be large enough to cause a full burial but can certainly knock you off your intended route and send you into unforgiving terrain. The avalanche danger is expected to rise dramatically overnight into tomorrow with a significant snowstorm on our doorstep. 


The BWRA remains closed to motorized recreation due to low snow depths in Sardine Meadows and the Leavitt Lake/108 junction. The BWRA is open to non-motorized use. If you are going to recreate, please be responsible and avoid off-road motorized riding. When visiting the Virginia Lakes area please remember to park respectfully so snow removal equipment has room to turn around. The road to Virginia Lakes will likely close for the season after tomorrow’s storm.



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.

Strong SW winds will transport 2-4” of new snow onto N-NE-E slopes creating cohesive winds slabs atop softer undisturbed snow. You will find these near wind sheltered features and convex slopes. In addition, cross loading may create wind slabs in unusual places like the lee side of ridges facing west to east.  Fresh wind slabs may be reactive to human triggers. Slopes with a smooth,  pillow like appearance should be approached with caution and avoided by using terrain to manage avalanche hazard. Watch for blowing snow and cracking underfoot to help inform your travel decisions.

Avalanche Character 2: Persistent Slab
Persistent Slab avalanches can be triggered days to weeks after the last storm. They often propagate across and beyond terrain features that would otherwise confine Wind and Storm Slab avalanches. In some cases they can be triggered remotely, from low-angle terrain or adjacent slopes. Give yourself a wide safety buffer to address the uncertainty.

Observations from the last two weeks show that the snow on north facing aspects remains very cold.  Low sun angles and short January days conspire to prevent direct sun from reaching most north to east facing slopes.  The lack of sun ensures weak snow remains weak.  In some N facing locations,  facets extend from the surface to ground level. More concerning are other isolated locations on N facing slopes, where layers of facets exist under the mosaic of the hard pack surface, creating strong layers atop weak layers. Be heads up when traveling on north aspects. Stop and assess the snowpack. A simple quick pit can reveal the presence of a persistent weak layer, vital knowledge before entering the terrain you wish to ski.

Snowpack Discussion

Wind slab formation will continue today with recent snow still available for transport, even though >1in. is forecast for today. Moderate SW wind speeds and the cold temperatures have resulted in low density snow that is easily transported. Be mindful of unforeseen weather differences caused by micro terrain that differ from the overall weather forecast. Such as the wind direction that varied yesterday between the forecasted SW wind in the BWRA and NE wind on Dunderberg peak. 


    As we all patiently await the arrival of the big storm, the BAC staff have discussed how the  density and temperature  of the incoming snow will affect cohesion with the existing snowpack. Forecasted 100+ mph wind speeds transport snow well below ridgelines in deposition patterns that are impossible to predict. We expect storm slabs and  wind slabs will form many times on the same slope during this unusually powerful storm. 

Storm snow could load the pre-existing snowpack with extraordinary loading rates. We do not know how the weak snow is going to react. If enough snow falls in a condensed period of time, the existing snowpack of today could fail, creating large avalanches. 

At this point, we want everyone to be aware that the upcoming storm has been described as a 20 year event.  Remember, unusual weather creates unusual avalanches. 

 We will be in the field seeking answers over the next few days. You can always help by submitting an observation. Observations related to weather, snowpack, and stability or even just photos help keep us all informed and safe in the backcountry.

recent observations

Light snow showers have been on and off again the last few days.

After last week's unseasonably warm temperatures a return to more seasonal temperatures has created a mosaic of surface conditions under 2-4” of new snowfall.2-4” dust on crust with small 8” thick isolated wind slabs in Virginia lakes zone.

SW wind observed in the BWRA, while NE wind observed in Virginia Lakes yesterday (1.25.2021)

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 7 deg. F.
Max. temperature in the last 24 hours: 21 deg. F.
Average wind direction during the last 24 hours: 3
Average wind speed during the last 24 hours: SW mph
Maximum wind gust in the last 24 hours: 10-20 mph
New snowfall in the last 24 hours: 2 in. inches
Total snow depth: 21 inches

We will see a break from recent snow showers today. Tonight, winter weather will ramp up as a powerful storm begins to take effect in the region. High rates of snowfall are expected, creating significant accumulation through Friday. In addition sustained 40-60 mph wind from the SW and gusts up to 100 mph are forecast. Snow totals may reach 1-3ft in the foothills and 3-6ft above 8000ft by Wednesday night. The next couple days ambient air temperature will reach highs in the 20s F

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 Mostly cloudy. Chance of snow in the evening, then snow after midnight Cloudy. Snow
Temperatures: 15 to 21 deg. F. 13 to 19 deg. F. 20-26 deg. F.
Wind direction: Light winds becoming southwest South South
Wind speed: 15 mph in the afternoon. Gusts up to 30 mph 15 to 25 mph. Gusts up to 50 mph 20 to 35 mph with gusts to 70 mph.
Expected snowfall: No accumulation in. 80% probability of 4 to 10 inches in. 90% probability of 12 to 20 inches in.
For above 10000 ft.
  Tuesday Tuesday Night Wednesday
Weather: Partly cloudy Mostly cloudy. Chance of snow in the evening, then snow after midnight Cloudy. Snow
Temperatures: 8 to14 deg. F. 6 to 11 deg. F. 13 to 19 deg. F.
Wind direction: West Southwest South
Wind speed: West 15 to 20 mph with gusts to 30 mph 25 to 35 mph with gusts to 60 mph increasing to south 30 to 50 mph with gusts to 85 40 to 60 mph with gusts to 100 mph
Expected snowfall: No accumulation in. 80% probability of 5 to 10 inches. in. 90% probability of 15 to 25 inches. in.

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.