Snowpack Summary published on March 31, 2018 @ 8:44 am
Issued by Ryan Lewthwaite -

bottom line:

The weather is rapidly warming with clear skies & temperatures reaching near 50F tomorrow. There is much evidence of Loose Wet & Cornice Avalanches that have occured. The riding is fun & mostly supportable under sled, but objects & creeks are melting out quickly. The launching of snowmobiles will climb up Hwy 108 each day as patches of asphalt emerge. Keep parking consistent while leaving an open lane egress for Marines & Caltrans mobility.

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.

Clearly we are diving into spring with temperatures reaching 50F above treeline tomorrow. Expect aspects that receive long durations of intense sun to be the most volatile for avalanches. The signs are there look for the clues such as: rollerballs, point releases originating from warm objects, surface shean or icy appearance, runnels, creeping snow, & corn.

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.

There is enough evidence to suggest that cornices are unstable. The unsupported nature of these hazards makes them difficult to predict when they may fail. Avoid being on or under any cornice today, they have a very large destructive potential. Refer to yesterday's observation of a combo cornice fall stepping into Deep slabs leftover from the latest storm system.

Snowpack Discussion

Melting at a rate of 2-4" per day is too rapid of a change for the snowpack. Without a refreeze at night due to atmospheric inversions expect snow to remain wet, unconsolidated & in motion. The larger slab avalanche problem is lessening but the Loose wet & Cornice problems are on the rise. Please don't get complacent with the beautiful weather..

recent observations

Loose wet & cornice avalanches will be the main components of our avalanche hazard for the next few days. Fairly deep wind slabs still exist on isolated leeward features, especially around Leavitt Cirque. Combination Loose wet/ cornice avalanches have been observed. The probability of a human triggering a deep slab is low but cornices falling from ridgelines could tip the scales in dramatic fashion. Rollerballs, wet point releases, stress-cracking, runnels, rivers & previous avalanche debris is showing itself with the rapid melting. 

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 34 deg. F.
Max. temperature in the last 24 hours: 55 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: 0 inches
Total snow depth: 63 inches

Warm & dry conditions will exist through the weekend & the middle of next week. We will see high clouds with temperatures reaching 50F degrees. Do not expect the diurnal refreeze at night due to inversions keeping higher elevations in warm air. Wednesday should bring us a weak disturbance possibly followed by some precipitation.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Saturday Saturday Night Sunday
Weather: Cloudy with decreasing clouds later. Partly cloudy then becoming clear. Sunny
Temperatures: 50 to 58 deg. F. 28 to 33 deg. F. 50 to 58 deg. F.
Wind direction: Light winds West Light winds
Wind speed: Light winds 10 to 15 mph; gusts to 30 mph late Light winds
Expected snowfall: 0 in. 0 in. 0 in.
For above 10000 ft.
  Saturday Saturday Night Sunday
Weather: Cloudy Partly cloudy then becoming clear. Sunny
Temperatures: 42 to 49 deg. F. 25 to 30 deg. F. 43 to 50 deg. F.
Wind direction: Southwest West Southwest
Wind speed: 15 to 25 mph; gusts to 35 mph 10 to 20 mph; gusts to 35 mph late 15 to 20 mph; gusts to 35 mph
Expected snowfall: 0 in. 0 in. 0 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.