THIS SNOWPACK SUMMARY EXPIRED ON January 18, 2019 @ 8:28 am
Snowpack Summary published on January 16, 2019 @ 8:28 am
Issued by Ryan Lewthwaite -

bottom line:

An AVALANCHE ADVISORY has been issued for the next 48 hours for the BWRAs. A very potent winter storm is approaching our region & will bring widespread avalanche activity. The complexity of the snowpack & the new snow variable has the Avalanche Hazard at HIGH. Your vulnerability to avalanches grows exponentially as you enter mountainous terrain during & after this storm. If you see an avalanche or investigate the snowpack give us your input so we can disseminate it to the public.

Avalanche Character 1: Storm Slab
Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.

The most anticipated & rumored storm is projected to drop up to a meter of new snow in a short time. All aspects & elevations are suspect to widespread avalanche activity. With the new snow, wind & lingering persistent problems, travel in avalanche terrain is not advised.

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.

Expect large amounts of snow to be displaced by Strong to Gale force winds during this storm. Southwest winds with gusts up to 125 mph will deposit slabs on aspects NW-N-SE. Eddying winds will create large Cornices, adding to the avalanche hazard.

Avalanche Character 3: 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 Persistent Slab problem that we have been documenting could reemerge as a Deep Slab issue with this potent storm. Adding mass & gaining depth, this unpredictable persistent layer may have enough stresses to fail widespread across mountain slopes. Increasing uncertainty of this reactiveness should prompt you to avoid or scrutinize areas with high consequence.

Snowpack Discussion

AVALANCHE ADVISORY for the NEXT 48 Hours! The approaching storm & forecasted new snow accumulations will create large natural avalanches with very destructive potentials. Lastnight at Sonora Snotel~8770' we gained 15" of new snow with strong ridgetop winds. The Persistent Weak Layer we have been tracking could reemerge as a DEEP SLAB problem tonight as we accumulate absurd amounts of precipitation on this already buried anomoly 2-3' down. The layer of Facets associated with this problem has been relatively dormant to test results lately, but the structure is especially worrisome with new mass adding stresses to it. 

recent observations

A great week for traveling in the mountains of the Eastern Sierra. Most of the soft & stable snow was pilllaged by recreationists in typically seasonable conditions. The observed Persistent Slab avalanche problem still lingers & grows depth within the snowpack. The potential for this problem to become a Deep Slab Avalanche issue has forecasters on our toes. Please submit snowpack & avalanche observations!

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 27 deg. F.
Max. temperature in the last 24 hours: 29 deg. F.
Average wind direction during the last 24 hours: South
Average wind speed during the last 24 hours: Moderate mph
Maximum wind gust in the last 24 hours: Strong mph
New snowfall in the last 24 hours: 15 inches
Total snow depth: 54 inches

Today scattered snow showers with significant accumulations tonight through Friday. An AVALANCHE ADVISORY is issued for the BWRAs begining this morning extending up to 48 hours from now. Winds from the Southwest will be at STRONG to GALE force with gusts reaching 125 at ridgeline. Whiteout conditions are expected with travel impacts, estimated mountain snowfall rates will be Heavy (S5) to VERY Heavy (S10), rain is possible at low valley elevations.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Mostly cloudy with scattered snow showers Snow Level Below 7000' Cloudy & snow Snow Level 7500' Cloudy & snow Snow Level Below 7000'
Temperatures: 31 to 37 deg. F. 23 to 28 deg. F. 30 to 38 deg. F.
Wind direction: Southwest South Southwest
Wind speed: 20 to 40 mph; gusts to 80 mph 30 to 45 mph; gusts to 85 mph 25 to 40 mph; gusts to 75 mph
Expected snowfall: 3 in. 13 to 21 in. 20 to 27 in.
For above 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Mostly cloudy with snow showers Snow Level Below 7000' Cloudy & snow Snow Level 7500' Cloudy & snow Snow Level Below 7000'
Temperatures: 24 to 30 deg. F. 17 to 22 deg. F. 25 to 30 deg. F.
Wind direction: Southwest Southwest Southwest
Wind speed: 40 to 70 mph; gusts to 95 mph 50 to 85 mph; gusts to 125 mph 45 to 70 mph; gusts to 110
Expected snowfall: 3 in. 17 to 25 in. 22 to 30 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.