THIS SNOWPACK SUMMARY EXPIRED ON January 9, 2018 @ 10:17 am
Snowpack Summary published on January 7, 2018 @ 10:17 am
Issued by Ryan Lewthwaite -

bottom line:

Evaluations are underway, although we are NOT OPEN to snowmobiling at this time. Another storm cycle is heading our way tonight, keep your fingers crossed. As new snow collects itself the avalanche hazard will remain elevated. Mild temps, wind, & a persistent slab problem plague our snowpack. Avalanches, both natural & human triggered were observed yesterday. Today we will get sun & warmth, giving us a look at the alpine for mid-storm avalanches. Although the possibility exists for not only slab issues but loose wet avalanches as the sun heats steeper slopes.

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.

New snow accumulated yesterday at treeline to nearly 7-8", & in the alpine to almost 12". Mild temperatures below 8500' brought wet & dense snow, whereas above that dry snow prevailed. Winds were strong, out of the Southwest with a gust to 73 mph recorded. The new snow particles were being compressed by the winds & creating a creamy appearance on the surface. The slabs that formed have a lot of mass & will be easy to trigger with the weight of a human.

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.

New accumulations sit atop of an older wind slab. Below that wind slab the metamorphism of snow grains has occurred, known as faceting. This process turns denser & more cohesive layers of snow into a loose & poorly bonded structure. The larger pore spaces & unstable array allow for avalanches to spread further across the slope, propagation.
This situation could persist for some time into the winter, or may never leave our avalanche hazard scheme.

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.

Mild temps below 8500' brought moisture rich snow to this elevation band. As the suns arch across the sky increases solar radiation & temperatures, its progress along different aspects will loosen snow sequentially. Roller balls & wet sluffs correlate to instability.

Snowpack Discussion

Time & wind will permit the new snow to gain strength. Previous storms have deposited wind slabs on North through Southeast aspects. The absence of precipitation & above normal temps for periods of our winter have allowed faceting to occur below these wind slabs. Facet layers below the slabs have been the failure point for many of the pit tests & suggest that this be a layer of concern.

recent observations

Natural wind slab avalanches were found on North through East aspects above treeline. Loose wet avalanches were observed on south facing slopes. The occurrence of human triggered avalanches on wind loaded slopes is likely.

weather

Depending upon your elevation wet snow & rain fell below 8500' & cold dry snow above that. Winds scoured & transported snow across the landscape creating slabs on North through East aspects. Today, spotty clouds & warmer temperatures in the morning & afternoon. Tonight another, hopefully more prolonged, system moves into our area bringing snow & mild temps tomorrow.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Sunday Sunday Night Monday
Weather: Partly cloudy with increasing clouds Mostly cloudy with a slight chance of snow late Cloudy with a chance of rain & snow
Temperatures: 43 - 49 deg. F. 29 - 35 deg. F. 39 - 45 deg. F.
Wind direction: Light winds Light winds South
Wind speed: Gusts to 25 mph Gusts to 25 mph increasing to 35 mph late 10 to 15 mph; gusts to 25 mph increasing to 45 mph later
Expected snowfall: 0 in. 0 in. 2 - 5 in.
For above 10000 ft.
  Sunday Sunday Night Monday
Weather: Partly cloudy with increasing clouds Mostly cloudy with a slight chance of snow late Cloudy with a chance of snow in the morning then snow in the afternoon
Temperatures: 38 - 43 deg. F. 24 - 29 deg. F. 33 - 38 deg. F.
Wind direction: Southwest Southwest South
Wind speed: 15 to 20 mph; gusts to 30 mph increasing 20 to 30 mph; gusts to 40 mph later 15 to 20 mph; gusts to 30 mph increasing 20 to 30 mph; gusts to 40 mph late 15 to 25 mph; gusts to 35 mph increasing 30 to 40 mph; gusts to 55 mph later
Expected snowfall: 0 in. 0 in. 3 - 6 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.