THIS SNOWPACK SUMMARY EXPIRED ON March 11, 2019 @ 8:25 am
Snowpack Summary published on March 9, 2019 @ 7:25 am
Issued by Ryan Lewthwaite -

bottom line:

Cold temperatures & plentiful winds from the South & West has created Large Wind Slabs & Cornices in the BWRA. Cornices have been releasing naturally on steep & above treeline ridges causing small avalanches within the new snow. Use caution when traveling near areas where new snow is being deposited by strong winds, as triggering a Large Wind Slab avalanche is still possible on isolated Lee features.

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.

The rapid transport of snow was observed all day in the mountains, especially above treeline where snow banners were present. The redistributed snow has been scattered unevenly across the landscape, being deposited to Wind Slabs on Lee aspects. Although stubborn to initiate in most locations, there is the liklihood of finding the sweet spot in a tappering Slab that could propagate failure.

Avalanche Character 2: Cornice
Cornice Fall avalanches are caused by a release of overhanging, wind drifted snow. Cornices form on lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth from wind drifting, rapid warming, or during rain-on-snow events. Cornices may break farther back onto flatter areas than expected.

I counted seven natural Cornice Fall avalanches in the Leavitt Cirque yesterday. South & West winds along ridgelines have created sharp & barrel-like snow waves on Lee aspects. These wind eddys help form the unsupported masses of snow that hang off exposed terrain features. The potential for these Cornices to fail when disturbed by a recreationist is high & can be catastrophic.

Snowpack Discussion

Wind Slabs & Cornices are the main features for todays avalanche Hazard. The Storm Slab instability has been subdude by constant winds from the South & West. Our snowpack is quite deep in Lee aspects near & below treeline with high variability across the landscape. On average depths range from 250cm to 350cm. The snowpack structure is gaining strength overall, except for isolated & overloaded Wind Slabs on North through East aspects. Large & dramatic Cornices can be found anywhere the winds have been able to eddy around terrain features. The layer of concern is a new snow/ old snow interface buried 45 to 55cm deep which is reactive to Hard forces in stability tests.

recent observations

~A natural Wind Slab avalanche was observed in Upper Horse Creek above Twin Lakes. The slide occurred between Matterhorn & Doodad Peaks on a steep North aspect around 11K'. Loose wet activity below 9000' was seen in the surface snow.

~In the BWRA large Wind Slabs & Cornices were seen on North through East aspects in all elevations. Seven Cornice Fall avalanches were observed in the Leavitt Cirque, entraining only Loose Dry snow, size D1. Wind Slabs have been growing thick with recent redistribution from South through West winds, but are stubborn to trigger.

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 15 deg. F.
Max. temperature in the last 24 hours: 24 deg. F.
Average wind direction during the last 24 hours: West
Average wind speed during the last 24 hours: Light mph
Maximum wind gust in the last 24 hours: Strong mph
New snowfall in the last 24 hours: 2 inches
Total snow depth: 108 inches
weather

A low pressure system will progress South along the CA coast bringing with it snow showers for the Sierra crest. Increasing clouds today will be accompanied by 2 to 4 inches of new snow by Sunday evening. Southwest winds will be moderate today through tonight & diminishing for Sunday & Monday. Monday will have scattered clouds & sun until the next precipitation band arrives late evening. Below average temperatures for the next few days may trend warmer by the later half of next week. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Saturday Saturday Night Sunday
Weather: Increasing clouds with a chance for afternoon snow showers. Snow Level Below 7000' Mostly cloudy with a chance for snow showers. Snow Level Below 7000' Cloudy with a chance for snow showers. Snow Level Below 7000'
Temperatures: 24 to 32 deg. F. 11 to 17 deg. F. 21 to 29 deg. F.
Wind direction: Southwest Southwest Light winds
Wind speed: 15 mph; gusts to 35 mph 15 mph; gusts to 25 mph. Light winds after midnight. Light winds
Expected snowfall: 1 in. 1 in. 1 to 4 in.
For above 10000 ft.
  Saturday Saturday Night Sunday
Weather: Increasing clouds with a chance for afternoon snow showers. Snow Level Below 7000' Mostly cloudy with a chance for snow showers. Snow Level Below 7000' Cloudy with a chance for snow showers. Snow Level Below 7000'
Temperatures: 16 to 22 deg. F. 5 to 10 deg. F. 14 to 20 deg. F.
Wind direction: Southwest Southwest Light winds
Wind speed: 15 to 30 mph; gusts to 45 mph 15 mph; gusts to 25 mph Light winds
Expected snowfall: 1 in. 1 in. 2 to 4 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.