THIS SNOWPACK SUMMARY EXPIRED ON January 31, 2018 @ 9:02 am
Snowpack Summary published on January 29, 2018 @ 9:02 am
Issued by Ryan Lewthwaite -

bottom line:

BWRA open! Get the forecast, & paint yourself recreating on a canvas of safety. The conditions for snowmobiling are good, for now. Snowpack stability has increased itself since we last received precipitation less than a week ago. Stay engaged in your chosen riding terrain as 3 avalanche problems still remain from our unseasonable season. As we see temps rise to near 50F degrees today loose wet avalanches will be of primary concern.

Avalanche Character 1: 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.

Most of the snow moving activity has involved the solar aspects & melting of surface layers. Temperatures are barely freezing at night leaving the uppermost snowpack in constant creep. Continuous periods lacking a refreeze does not bode well for our snows longevity. Reaching highs of 50F degrees during the day in February is uncommon. Although not relatively large in size a wet loose avalanche has the possibility to knock you off your intended route & into terrain that is undesirable.

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.

Varieties of wind slab are noticeable, especially above treeline. Most are soft & unsupportable but some are firm & can hold the weight of sled & rider. The slabs that can support weight & are hollow sounding are to be avoided. These stronger slabs can likely fail catastrophically & propagate above you, entraining more snow from starting zones. Pay close attention to the aspect you intend to ride, North through East aspects have been loaded.

Avalanche Character 3: 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.

Let us not forget about the deeper buried weak facetted layers that linger in the snowpack. The depth of these weak layers is variable across the landscape (50 to 80cm below surface) but its availability is constant. While snowmobiling a keen observer can notice whumphing & collapsing underneath them, indicative of potential avalanching.

Snowpack Discussion

We are transitioning to a more spring-like snowpack with temperatures at night barely freezing. Surface layers are getting rapidly warmed & loose wet avalanches are occurring on solar aspects. Wind slab are variable with hollow pockets underneath the more supportable slabs. The snowpack is showing wind effected layers sandwiched by melt-freeze crusts, with a persistent (facetted) weak layer below 60cm (23") within treeline areas. The thin veneer of snow that exists below 8500' is melting away quickly. Percolation of melting surface snows may lubricate underlying layers & cause shear failures.

recent observations

We have been snowmobiling the BWRA for two days & observations have been positive for those recreating. Slopes are holding in tact on leeward aspects that have developed soft wind slabs. Areas that are on solar aspects have shown roller-balls & wet avalanche actively, & riders are avoiding them. ESAC was submitted an avalanche observation from Virginia Lakes that is worth reading.

http://www.esavalanche.org/content/avalanche-virginia-lakes

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 31 deg. F.
Max. temperature in the last 24 hours: 51 deg. F.
Average wind direction during the last 24 hours: Northeast
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: 23 inches
weather

Hot & annoying weather is predicted for the future week. Temps in the high 40's to low 50's is forecasted with no precipitation in sight. Thin snow coverage is being replaced with bare ground (mud) & greening vegetation. Winds will come from the West with moderate severity, & no snow is available for transport.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Monday Monday Night Tuesday
Weather: Partly cloudy Mostly cloudy Partly cloudy
Temperatures: 47 - 53 deg. F. 26 - 32 deg. F. 50 - 58 deg. F.
Wind direction: Southwest West West
Wind speed: 10 to 15 mph; gusts to 30 mph later 10 to 15 mph; gusts 25 to 35 mph late 15 to 25 mph; gusts to 45 mph
Expected snowfall: 0 in. 0 in. 0 in.
For above 10000 ft.
  Monday Monday Night Tuesday
Weather: Partly cloudy Mostly cloudy Partly cloudy
Temperatures: 40 - 45 deg. F. 24 - 29 deg. F. 44 - 50 deg. F.
Wind direction: West West West
Wind speed: 15 to 20 mph; gusts to 35 mph later 15 to 25 mph; gusts to 40 mph 20 to 30 mph; gusts to 50 mph
Expected snowfall: 0 in. 0 in. 0 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.