THIS SNOWPACK SUMMARY EXPIRED ON February 2, 2018 @ 9:26 am
Snowpack Summary published on January 31, 2018 @ 9:26 am
Issued by Ryan Lewthwaite -

bottom line:

Rapid warming is loosening our thin snowpack & will remain our concern in a variety of forms. Wet loose avalanche activity is the result of water percolating through the snow grains & destroying the bonds that unite the pack. Avalanche problems can be in the form of loose wet, wet slab, or cornice failure types. Afternoon travels can become hazardous when the sun & air temperatures are most intense. We are losing an average of 2" per day on our slopes exposing more environmental & route finding issues. There is a long ride on asphalt before you hit snow at 8500' from the Leavitt Falls Vista Gate. Friday & Saturday we will be having a Snowmobile Specific Avalanche Awareness Class in Gardnerville. We would like to see you there.

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.

Temperatures near 50F degrees cannot sustain a strong snowpack for very long. The rapid increase in wet instabilities is directly due to sun & warm air temperatures. Look for the more shaded aspects for the best snow, especially in the afternoon when the loose activity is most pronounced. Relatively small in size, a loose wet avalanche can send you into a terrain trap, over a rock band or into the trees unwillingly.

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.

On ridgelines & some vertical terrain features, winds help create larger accumulations of snow on leeward aspects. When this develops a cornice, unsupported overhanging snow, the potential for this drift to fall & create a large avalanche is nearly inevitable. Cracks were easily seen in cornices yesterday, as wet snows have begun to creep along with gravity. Look up & take notice of dangers above you every time you ride.

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.

Weak layers remain within our snowpack where facets & surface hoar exist. As you dig a test pit look for layers that have poor resistance & are likely to just fall out of your snow pit walls. These grains do not support rapid weight changes well. What they do well is collapse & propagate avalanches. It may be hard to get a catastrophic failure but do not exclude this hazard from your decision making repertoire. Yesterdays pit revealed this problem to be 26cm (10") deep.

Snowpack Discussion

Observations from treeline yesterday on a North & East aspect showed a pack of 135cm (53"). Surface melting was apparent on solar aspects, & only isolated pockets contained dry snow not effected by sun & wind. Yesterday's observation showed that 26cm (10") deep exists our persistent slab problem which was the interface where failures in test were occurring. Although stubborn to initiate & propagate collapse, this layer still contains facets & some buried surface hoar which are in the process of rounding. The rounding of these problem grains can improve stability. Temperatures are continuously above freezing in the alpine & percolation of water through the snowpack will degrade bonds amongst snow grains decreasing stability. A density change in the uppermost wind effected layer has also shown to be a moderately weak interface

recent observations

Cornices can have catastrophic failures from rapid melting & loosening of snow grains. Pictures from yesterdays observation clearly show South facing cornices are primed to break away from the ridgeline. Cornices can be a dramatic avalanche problem, especially when then they fall in an already loaded starting zone creating wet slab & loose wet avalanches. Pinwheels & rollerballs are putting a fine texture to our rapidly melting slopes & are a great indicator of wet instabilities. Creeks, rocks, asphalt & vegetation are melting out creating harsh riding conditions especially below 8500' elevation.

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 38 deg. F.
Max. temperature in the last 24 hours: 50 deg. F.
Average wind direction during the last 24 hours: West
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: 20 inches
weather

Hot, dry & devoid of snow. At the rate of losing almost 2" of snow each day we are struggling to keep a snowpack near 8500'. Blocking High Pressure has consumed our region & any precipitation is going to the Northwest. Mount Baker is the place to be if you want deep pow right now, they are having a record January. Clouds tomorrow will help curtail some sublimation & melting.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Sunny Partly then mostly cloudy late Mostly cloudy
Temperatures: 50 - 56 deg. F. 29 - 34 deg. F. 46 - 54 deg. F.
Wind direction: West Light winds Light winds
Wind speed: 10 to 15 mph; gusts to 30 mph then winds diminish Light winds Light winds
Expected snowfall: 0 in. 0 in. 0 in.
For above 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Sunny Partly then mostly cloudy late Mostly cloudy
Temperatures: 43 - 48 deg. F. 26 - 31 deg. F. 39 - 45 deg. F.
Wind direction: West Northwest West
Wind speed: 15 to 25 mph; gusts to 35 mph 10 to 15; gusts to 25 mph winds diminish late 10 to 15 mph; gusts to 25 mph later
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.