Snowpack Summary published on March 24, 2018 @ 9:22 am
Issued by Ryan Lewthwaite -

bottom line:

Complexities exist within our variable snowpack. The latest storm brought with it extreme winds, dense wet snow & rain to many locations. Upon visual inspection a savvy traveler can see the evidence of avalanches very large in size(R3.5D3). Gullies & terrain traps are filled with debris, while cornices & crowns can be seen all over the BWRA. There is a deep water hazard on Hwy 108 near the climbing wall & campground, with a fairly sketchy detour. We Need Public Observations, please!

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.

The strong SW winds have deteriorated & transported most powder snow accumulations. The prevailing W-SW-S winds will continue to load E-NE-N aspects in dramatic fashion. These leeward slopes are holding the thickest snow depths, some are found to be over 300cm (118"). Some slopes above treeline look like wavy sand dunes in texture with billowing shapes on roll-over convexities. Gusts yesterday near 50 mph at ridgeline have formed long sensitive Wind slabs that could fail with the added weight of a traveler & their entourage.

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.

The elusive Deep slab avalanche problem has been showing itself with last weeks storm & more noticably with the latest precipitation. Wind slabs that are releasing can potentially step-down into older buried weak layers where cohesionless persistent grains linger. Although isolated, as a slab avalanche runs over an area where another deep slab has a thin spot, that action could trigger deep pockets of snow to release. As seen in the "Leavitt Region" & "Sonora Pass Avalanche" observation photos.

Avalanche Character 3: Cornice
Cornice Fall avalanches are caused by a release of overhanging, wind drifted snow. Cornices form on lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth from wind drifting, rapid warming, or during rain-on-snow events. Cornices may break farther back onto flatter areas than expected.

Cornices are large & tender in the BWRA. We will commonly see cornices that fall trigger slab avalanches that propigate across a starting zone. We see cornice fall activity days after a storm & especially during periods of rapid warming & wind loading.  

Snowpack Discussion

A complex array of avalanche problems encompass our hazard for the next few days. Lots of dense wet snow & rain fell with strong to extreme winds in the BWRA for a few days. Accumulations are unsettled, in constant transport, & readily forming slabs that are sensitive will avalanche with the right mechanism. The growing snowpack on lee aspects will continue throughout today & increase instability. Deep slab potentials are hiding within the variable snowpack, some as deep as 13'. Rain has seriously effected riding quality at nearly all elevations.

recent observations

Yesterdays clear skies allowed for a visual of the avalanche activity that happened during our wet, windy & wild storm. Very large in size R3.5 with the destructive potential of D3 makes these avalanches deadly to humans who are victims of them. Seeing snowmobilers who don't carry transcievers, with rescue equipment attatched to their sled tunnels, with friends watching in a runout zone, traveling up a 35 degree slope five at a time; is a potential disaster! Please discuss unsafe riding practices with your firends & think in worst-case-scenarios. The decisions you make, while blinded by having fun, can have huge consequences...

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 21 deg. F.
Max. temperature in the last 24 hours: 34 deg. F.
Average wind direction during the last 24 hours:
Average wind speed during the last 24 hours: mph
Maximum wind gust in the last 24 hours: mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 75 inches

A cool clear morning will give way to partly cloudy skies & afternoon snow showers. Winds will be less dramatic today out of the SW 15 to 25 mph; gusts to 40 mph. A diurnal refreeze has taken effect overnight. This lock-up will create icy conditions early & make wind slabs tender. No major accumulations expected with the orographic lift today & tomorrow. The precipitation that does fall may be in the form of ice chips or hard rain at lower elevations. Warm springlike conditions will engulf our weather pattern from Tuesday on into the weekend.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Saturday Saturday Night Sunday
Weather: Sunny then increasing clouds with scattered snow showers. Partly cloudy with scattered snow showers. Partly cloudy with isolated snow sowers.
Temperatures: 26 to 34 deg. F. 9 to 15 deg. F. 24 to 30 deg. F.
Wind direction: Southwest Southwest West
Wind speed: 15 to 25 mph; gusts to 40 mph 15 to 25 mph; gusts to 40 mph 10 to 15 mph; gusts to 30 mph
Expected snowfall: 1 in. 2 in. 0 in.
For above 10000 ft.
  Saturday Saturday Night Sunday
Weather: Partly cloudy with scattered snow showers. Mostly cloudy decreasing to partly cloudy with scattered snow showers. Partly cloudy with isolated snow showers.
Temperatures: 20 to 26 deg. F. 3 to 8 deg. F. 16 to 22 deg. F.
Wind direction: Southwest Southwest Southwest shifting West
Wind speed: 30 to 45 mph; gusts to 55 mph decreasing to 20 to 30 mph; gusts to 45 mph later 25 to 35 mph; gusts to 55 mph decreasing to 45 mph late 20 to 30 mph becoming West 10 to 15 mph; gusts to 25 mph later
Expected snowfall: 1 in. 2 in. 0 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.