Snowpack Summary published on March 21, 2018 @ 9:20 am
Issued by Ryan Lewthwaite -

bottom line:

A warm & moisture abundant atmospheric river has entered our area & will reside until Friday morning with a possible +4' expected. Rain will fall at higher elevations in the mountains with fluctuating freezing levels throughout the storms duration. Precipitation will become most dramatic tonight into tomorrow with winds likely to gust over 100 mph in the alpine out of the Southwest. Avalanches will be occuring due to variety of problems including: Wet slab, Loose wet, Wind slab, Storm slab, Loose dry, Cornice fall & the vicious Deep slab. Within the past few days rapid warming has triggered these deep lingering weak layers, possibly associated with graupel from the last onslaught of snow

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.

Saturation of snow from rain & warmth will be loosening & lubricating the snowpack. To what degree will this influence avalanches is yet to be seen, but anticipate this problem at lower elevations around 8500' & especially on aspects NE-E-SE. These aspects hold the deepest snowpack & isolated areas that haven't been effected by reoccuring avalanches could be ripe for release. Incorporate the potential Deep slab issue here as slabs have been observed stepping down into older weak snow layers. Look for stress-cracking on convexities & cornices, sometimes you can hear the creep or glide of the snowpack during movement.

Avalanche Character 2: 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.

Winds as usual will be transporting snow to features within the landscape allowing for really deep pockets & cornices. Wet snow has an amazing ability to stick to very steep slopes & make unique wind wave & cornice features, which are tender. Southwest winds will prevail, with possible gusts to 105 mph during tomorrows daylight hours. Expect slabs to be a variety of firm & moist with water looking for the path of least resistance on the surface, we call these channels "Runnels".

Avalanche Character 3: 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.

Loose wet indicators will be most readily apparent on all aspects & mostly lower elevations where rain dominated. Near & above freezing temperatures up to our remote weather stations at 9604' can tell you that the diurnal lock-up may not have happened, leaving the snowpack in perpetual motion. One of my favorite phenomenons is likely to be seen today the "Pushalanche". This is where the localized snow underfeet packs well enough to an old interface where it slides small & quite uniformily, collecting upon itself.

Snowpack Discussion

Our winter recreation area has a dynamic weather system currently influencing rapid change of our snowpack. Surface loose wet instabilities, mid pack slabs & buried deeper weak layers are at a constant battle with environmental change. An additional accumulation of 4- 5' of new snow & a few inches of rain, will tip the balance & we will definately see avalanches of large size & destructive force.

recent observations

Sun & warmth have changed our powder to chowder. The addition of rain will make our situation more soupy & prone to avalanching. Two natural avalanches this week, in the Sonora Pass area, have shown us that the Deep slab instability is a reality for us. A +6' crown was observed on a convex rollover that encompassed a few of the  avalanche problems, ultimately releasing on a weak layer from earlier in the season.

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 35 deg. F.
Max. temperature in the last 24 hours: 40 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: 3 inches
Total snow depth: 61 inches

~Winter Storm Warning is in effect until 5AM Friday~ 

A warm, moisture rich storm is upon us. Rain is likely to be seen throughout the day with a fluctuating freezing level above 8500' in some areas. Winds will be moderate to strong out of the SW & gusts could be seen over 100 mph tomorrow. Snotel sites are telling us we may have received 4-6" snow with 1.5- 2" of snow water equivalent. The snow will be saturated. Above & near freezing temperatures lastnight in the BWRA coupled with over 4' of snow expected will make our snowpack very sensitive to change & human travel on steep slopes. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Cloudy with a chance of rain & snow. Cloudy with rain & snow. Cloudy with rain & snow
Temperatures: 39 to 45 deg. F. 31 to 36 deg. F. 33 to 39 deg. F.
Wind direction: Southwest South Southwest
Wind speed: 15 to 25 mph; gusts to 45 mph 15 to 30 mph; gusts to 50 mph 15 to 25 mph; gusts to 45 mph
Expected snowfall: 1 to 5 in. 7 to 15 in. 11 to 19 in.
For above 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Cloudy with snow. Rain possible. Cloudy with snow. Cloudy with snow.
Temperatures: 31 to 36 deg. F. 25 to 30 deg. F. 27 to 32 deg. F.
Wind direction: Southwest Southwest Southwest
Wind speed: 30 to 45 mph; gusts to 70 mph increasing to 40 to 55 mph; gusts to 80 mph later 40 to 55 mph; gusts to 85 mph 50 to 70 mph; gusts to 105 mph decreasing to 45 to 60 mph; gusts to 95 mph later
Expected snowfall: 1 to 5 in. 12 to 20 in. 19 to 27 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.