Snowpack Summary published on April 7, 2018 @ 10:48 am
Issued by Ryan Lewthwaite -

bottom line:

Will temperatures get cold enough to snow at the higher elevations? The atmospheric river we are experiencing is warm & wet to around 11,000' with strong Southwest winds. The most worrisome avalanche problem for the BWRA is the likelihood of large destructive Wet Slab avalanches, especially on leeward aspects N-NE-E (R3D4). Expect steep terrain to be shedding snow off of the mountains & not so much collecting it. The avalanche hazard comes with plenty of problems, unless you are absolutely sure of your surroundings, travel in avalanche terrain is not recommended.

Avalanche Character 1: Wet Slab
Wet Slab avalanches occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoid avalanche terrain when you see pinwheels, roller balls, loose wet avalanches, or during rain-on-snow events.

The most destructive problem at the moment is the likelihood of large Wet Slab avalanches! The snowpack in leeward drainage features on N-NE-E aspects, near treeline, could be around 300cm deep. Taking on this massive deluge of rain, the snowpack will become saturated until it cannot hold together any longer. Gravity will overcome the shear strength of the snowpack creating large Wet Slab avalanches, some could be Deep. If enough rain falls, could full depth Glide avalanches be seen...?

Avalanche Character 2: Loose Wet
Loose Wet avalanches occur when water is running through the snowpack, and release at or below the trigger point. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Looking outside, there is no doubt that the mountains are shedding Loose Wet avalanches. Lubricated snow grains have poor cohesion & cannot resist gravity, therefore they slump off anything with a steep enough slope. Yesterday we saw plenty of Loose wet activity, some slides incorporated mud & rocks. Expect snow to be perfect for post-holing & getting your snowmobile stuck, there is no support.

Avalanche Character 3: 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.

This is the unknown? Will it get cold enough to snow at higher elevations? If we get the 4-10" of possible accumulations we could see moderate sized Wind Slab develop on N-NE-E aspect above treeline. The winds will accompany this system with voracious force nonetheless. Trees will be damaged with the strong Southwest winds.

Snowpack Discussion

Surprising depths of around 300cm still exist in isolated areas on N-NE-E aspects. These thick wind deposits in leeward drainage features are to be avoided for the next few days as they contain potential Deep Slab Avalanches. As we collect torrential rains within the snowpack expect to see natural avalanches that could reach R3D4 in size & destruction. Human triggered avalanches will be very likely if not certain on such terrain below, near & above treeline. Runnels & shmooing Loose wet slides will be all across the ladscape today. Travel is not recommended on any steep terrain above 30 degrees, or any areas where avalanches could increase consequences.

recent observations

We scouted for the avalanche remnants from the cycle post 3/22 & found plenty of large wind slab avalanches. A very wet afternoon yesterday with sideways rain & 38F degrees at 9K'. The snow was super saturated with Loose wet & Wet Slab avalanches seen through the clouds around Sardine Falls. Debris including mud & rocks were entrained in several of the wet avalanches. The percolation of rain water has likely run through the snowpack & onto the surface soils in some areas. Could we see a Glide Avalanche?

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 46 deg. F.
Max. temperature in the last 24 hours: 46 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: 51 inches

Rain in overwhelming amounts is impacting our area. Elevations around 11,000' will experience warmth, rain & strong SW winds. Snow is possible above treeline as temperatures decrease later today. The AR could deposit another 1-1.5" of water or 4-10" of snow depending on the systems development.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Saturday Saturday Night Sunday
Weather: Cloudy with rain. Snow level 11K' decreasing to 9K' Partly cloudy becoming clear. Snow level 7K' & below Sunny
Temperatures: 43 to 49 deg. F. 23 to 28 deg. F. 47 to 55 deg. F.
Wind direction: Southwest Southwest Southwest
Wind speed: 20 to 30 mph; gusts to 65 mph 20 to 30 mph; gusts to 55 mph 10 to 15 mph; gusts to 50 mph becoming light
Expected snowfall: 0 in. 0 in. 0 in.
For above 10000 ft.
  Saturday Saturday Night Sunday
Weather: Cloudy with rain. Snow level 11K' decreasing to 9K' SWE= 1 to 1.5" Partly cloudy becoming clear. Snow level 7K' & below Sunny
Temperatures: 37 to 42 deg. F. 19 to 24 deg. F. 42 to 47 deg. F.
Wind direction: Southwest Southwest West
Wind speed: 45 to 65 mph; gusts to 95 mph decreasing 35 to 55 mph; gusts to 75 mph later 30 to 50 mph; gusts to 75 mph 30 to 40 mph; gusts to 70 mph decreasing 15 to 25 mph; gusts to 45 mph later
Expected snowfall: 4 to 10 in. 0 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.