THIS SNOWPACK SUMMARY EXPIRED ON March 11, 2021 @ 8:36 am
Snowpack Summary published on March 10, 2021 @ 8:36 am
Issued by Jason Mozol - Bridgeport Avalanche Center

bottom line:

The avalanche danger increased significantly overnight. Human triggered avalanches in the fresh snow are likely today. 3-6 inches of snow fell last night with moderate to strong southerly winds and it is forecasted to continue snowing and blowing today. Fresh, sensitive, and growing wind slabs near and above tree line are the primary avalanche concern but also look out for storm slabs and loose dry avalanches in protected steep terrain. Avoid wind loaded avalanche terrain and watch for signs of instability like cracking and collapsing. Cautious route finding and conservative decision making are essential to account for the dangerous avalanche conditions.

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.

Fresh, sensitive, and growing wind slab avalanches are likely today near and above tree line on slopes facing W-N-SE. Another 1-5” of snow is forecasted today with moderate to strong SW winds that will continue to grow the wind slabs. These fresh wind slabs likely won’t bond well to the variety of old snow surfaces (wind board, near surface facets, sun crusts). Look out for blowing snow, cornice growth, cracking/collapsing, upside-down feeling snow, and smooth/rounded looking snow surfaces. Wind slabs are generally found on the leeward side of ridges and in cross loaded gullies. Avoid wind loaded avalanche terrain 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.

As the snow continues to fall today, storm slab avalanches will become possible on steep slopes protected from the wind near and below tree line. These will be most likely in areas with the deepest snowfall accumulations. Cracking and collapsing are sure signs to stay off of steep slopes. If you don’t find these signs of instability, expect loose dry avalanches easily running on the old slick snow surfaces in steep terrain.

Snowpack Discussion

We have had a relatively stable snowpack with little fresh snow for the last several weeks. That changed last night. Today we need to wake up our brains and get them back to thinking about avalanches. Be sure to change your travel practices today to account for the increased avalanche hazard in the backcountry. 

Continued light snowfall, shifting winds, and slow-to-bond slabs will keep avalanches sensitive for at least the next few days. Be on the lookout for winds shifting to the north tomorrow. Wind slabs may be redistributed to unusual aspects so stay alert.

recent observations

3-6” of snow overnight and moderate to strong S winds falling on widespread hard/slick surfaces and near surface facets on protected northerlies.

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 14 deg. F.
Max. temperature in the last 24 hours: 22 deg. F.
Average wind direction during the last 24 hours: S
Average wind speed during the last 24 hours: 20-30 mph
Maximum wind gust in the last 24 hours: 47 mph
New snowfall in the last 24 hours: 3-6 inches
Total snow depth: 90 inches
weather

A cold Pacific storm will continue to bring us snow showers through tomorrow. There is a slight chance of lightning this afternoon. Moderate to strong SW winds today will eventually shift to the north tomorrow. Drier and warmer weather is forecasted for Friday and Saturday.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Snow showers likely through the day. Slight chance of thunderstorms in the afternoon. Mostly cloudy. Chance of snow showers through the night. Mostly cloudy. Chance of snow showers through the day.
Temperatures: 19 to 29 deg. F. 6 to 14 deg. F. 21 to 29 deg. F.
Wind direction: Southwest West North
Wind speed: 15 to 30 mph with gusts to 50 mph. 15 to 30 mph. Gusts up to 50 mph decreasing to 35 mph after midnight. Light winds becoming north around 15 mph with gusts to 35 mph in the afternoon.
Expected snowfall: 70% probability of 1 to 5 in. 30% probability of 1 to 3 in. 60% probability up to 1 in. 40% probability of 1 to 2 in. Up to 1 in.
For above 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Snow showers in the morning, then snow showers likely and slight chance of thunderstorms in the afternoon. Mostly cloudy. Chance of snow showers. Mostly cloudy. Slight chance of snow showers in the morning, then snow showers likely in the afternoon.
Temperatures: 10 to 18 deg. F. 0 to 6 deg. F. 13 to 21 deg. F.
Wind direction: Southwest Southwest Northwest
Wind speed: 20 to 35 mph with gusts to 55 mph. 20 to 30 mph with gusts to 50 mph decreasing to around 15 mph with gusts to 35 mph after midnight. 15 to 20 mph. Gusts up to 25 mph increasing to 35 mph in the afternoon.
Expected snowfall: 80% probability of 1 to 5 in. 20% probability of 1 to 3 in. 60% probability up to 1 in. 40% probability of 1 to 2 in. Up to 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.