THIS SNOWPACK SUMMARY EXPIRED ON January 15, 2017 @ 8:00 pm
Snowpack Summary published on January 13, 2017 @ 8:00 am
Issued by Kyle Van Peursem - Bridgeport Avalanche Center

bottom line:

The snowpack is the BWRA will begin to heal and stabilize and the avalanche danger will decrease through the weekend.  Though conditions will finally be settling down, don't let your guard down as human triggered avalanches will still be possible, especially on wind loaded slopes.  There is still the potential for a smaller avalanche to step down and trigger a large and destructive deep slab avalanche, which could break 5-10 ft, or even 15 ft in heavily wind loaded areas.  Though the weather will be beautiful and the mountains choked with new snow this weekend, now is not the time to ride the most aggressive slopes.

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.

Strong winds out of the SW combined with many feet of snow have likely created large wind slabs on exposed slopes with a NW-N-SE aspect.  These have had time to strengthen and will be difficult to trigger, but still possible and could be very large.  Additonally, moderate winds out of the SE today will easily transport low density snow that fell yeserday, forming sensitive wind slabs on upper elevation exposed S-SW facing slopes.  Pay attention to wind loading and cross wind loading of terrain features.  Look for blowing snow, new cornice formation, and wind pillows to help identify where wind slabs are developing.  Large cornices continue to exist along ridgelines, extra caution is advised around these hazards.  It is best to avoid these features and stay off any previously wind loaded slope steeper than 35 degrees.  

Avalanche Character 2: 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.

Weak surface snow formed during the last week of December has been subsequently buried by up to 10-15 ft of new snow in the upper parts of the BWRA.  This layer has already been reactive since then, leading to numerous large and destructive natural avalanches in the rec area (see observations page for more details).  Luckily, heavy rain last Sunday helped to destroy this layer for locations below 9500', and subsequent refreezing of the wet snow will help to solidify the snowpack.  For upper elevations, not enough rain fell to percolate down to this layer and it still may be present and reactive on northerly slopes above 9500'.  Though triggering this layer is unlikely, smaller avalanches (i.e., wind slabs) may potentially step down to this layer and could produce historically large and destructive avalanches that would most certainly be unsurvivable.  These type of avalanches are notoriously difficult to predict and can propagate much longer and wider than expected.  Tracks on slopes are not an indicator of stability for these types of avalanches!  Your best bet is to stay off of steep (> 35 degrees) upper elevation (>9500') northerly slopes, especially if it appears it has been previously wind loaded.

Snowpack Discussion

The Sierras have been in an epic storm cycle over the past 10 days.  Since Jan 2nd, the Sonora Pass SNOTEL station has recorded nearly 13 inches of water and a snow depth increase of about 5 ft, with the current snow depth at 85 inches, or 7 ft.  Higher up, the Leavitt Lake SNOTEL station has recorded an astounding 27 inches of water and a snow depth increase of about 9 ft, with the current snow depth at 165 inches, or nearly 14 ft!  A deep and warm snowpack generally means a stable snowpack.  For the most part, this will be the case over the weekend but the potential for a wind slab avalanche stepping down to the buried weak layers from the last week in December is possible.  If caught in this type of slide, the chances of you surviving are slim to none as the slide could fail 10 - 15 ft below the surface.  Avoiding slopes where this layer still exists (upper elevation steep northerly slopes) will be the best strategy to avoid triggering these kind of avalanches.  Conditions will be spectacular this weekend and good riding will be found all over the BWRA.  Avoid the temptation to travel into terrain where a large deep slab avalanche may be triggered, even if you see other tracks.  The risk and consequences are just not worth it right now.

recent observations

Unfortunately, due to the conditions we have been unable to make it very far into the BWRA this past week.  We observed large debris piles from several massive wet slab avalanches just above Leavitt Lake Road that released last Sunday/Monday due to the heavy rain.  It is likely that numerous large avalanches have run over the past week, but have been filled in and covered up from the consistent heavy snow.  We will be out there today (Friday) and report back what we found.

weather

We finally get a breather from the nearly continuous storm cycle over the past week and a half.  High pressure moves in today with clearing skies and cooler temperatures through the weekend.  Another atmospheric river event looks to set up by the middle/end of next week. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Friday Friday Night Saturday
Weather: CLOUDY THEN BECOMING MOSTLY CLOUDY. SCATTERED SNOW SHOWERS IN THE MORNING, THEN ISOLATED SNOW SHOWERS IN THE AFTERNOON. PARTLY CLOUDY. SLIGHT CHANCE OF SNOW IN THE EVENING. PARTLY CLOUDY
Temperatures: 21-26 deg. F. 7-15 deg. F. 29-34 deg. F.
Wind direction: NORTHEAST
Wind speed: 10 TO 15 MPH WITH GUSTS TO 30 MPH LIGHT LIGHT
Expected snowfall: NONE in. NONE in. NONE in.
For above 10000 ft.
  Friday Friday Night Saturday
Weather: CLOUDY THEN BECOMING MOSTLY CLOUDY. SCATTERED SNOW SHOWERS IN THE MORNING, THEN ISOLATED SNOW SHOWERS IN THE AFTERNOON. PARTLY CLOUDY. SLIGHT CHANCE OF SNOW IN THE EVENING. PARTLY CLOUDY
Temperatures: 16-22 deg. F. 9-14 deg. F. 25-31 deg. F.
Wind direction: NORTHEAST EAST
Wind speed: 15 TO 20 MPH WITH GUSTS TO 35 MPH 15 TO 20 MPH WITH GUSTS TO 30 MPH. LIGHT
Expected snowfall: NONE in. NONE in. NONE 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.