THIS SNOWPACK SUMMARY EXPIRED ON April 13, 2017 @ 11:26 am
Snowpack Summary published on April 10, 2017 @ 11:26 am
Issued by Ryan Lewthwaite -

bottom line:

Sun & warming temperatures are forecasted for our area early this week.  Melting surface snow & the potential for Loose Wet Avalanches will be the primary concern for the next few days. Include potential Cornice failure in the Loose Wet Avalanche consideration, as this has been the trigger for the avalanches we've seen lately. Around 50 cm of new snow fell during our storm on Friday & Saturday, increasing the avalanche danger. Strong winds have deposited new snow on leeward aspects from the North through Southeast & stiff slabs have formed. As these slabs begin to settle & sinter to the old melt-freeze crust we can expect them to increase in stability over time. Making appropriate terrain selections & timing of the afternoon warm-up should dictate your travel plans. A quick pulse of moisture is predicted for Wednesday night into Thursday.

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.

We will see a return to spring-like temperatures around the Sierra Mountains early this week. Intense solar radiation in the afternoon will melt the new surface snow, making it more suseptable to human triggering on slopes steeper than 35 degrees. Adjust your riding plans when you notice a glazing & lustrious appearance to the snow surface & when your track begins to sink more than usual.

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.

Most of the avalanches that have been seen are the result of naturally occurung cornice falls. Another product of afternoon solar radiation & temperature increase is that cornices will become deformed & slowly creep untill the bonds that hold it together reach the point of collapse. Dripping & small chunks of cornice falling mid-day are good indicators of cornice instability.

Avalanche Character 3: 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 new snow that fell on Friday & Saturday still needs time to sinter to the old melt-freeze crust that exists below it. Strong winds have scattered the precipitation to loading zones on aspects from South through Northeast. Winds have elongated this slab, in areas with substantial fetch, lower on the slope than is normally expected.

Snowpack Discussion

The 50cm that fell at the end of last week was wind effected. The new snow sits atop an older melt-freeze crust which through stability testing has proven to be the interface of concern. A moderate to hard force was allowing this slab to propigate, in planar fracture, the uppermost & unstable new snow surface. 

recent observations

Localized Cornice collapses have been the catalyst for the avalanche activitey seen in the past two days.


Rapid mid-day warming will change the stability of the surface snow making it loose & easily triggered. Mild evenings will exacerbate this thawing process.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Monday Monday Night Tuesday
Weather: Partly cloudy Partly Cloudy Mostly cloudy. Slight chance of snow in the morning, then chance of snow in the afternoon
Temperatures: 40-46 deg. F. 22-28 deg. F. 42-48 deg. F.
Wind direction: NA NA Southwest
Wind speed: Light Light, Gusts up to 25 mph after midnight Winds 10 to 15 mph with gusts to 40 mph
Expected snowfall: 0 in. 0 in. 0 in.
For above 10000 ft.
  Monday Monday Night Tuesday
Weather: Partly Cloudy Partly Cloudy Mostly cloudy. Slight chance of snow in the morning. Chance of snow in the afternoon
Temperatures: 34-40 deg. F. 18-24 deg. F. 37-43 deg. F.
Wind direction: Southwest Becoming South Southwest
Wind speed: Winds 10 to 15 mph with gusts to 30 mph in the morning becoming light Light winds 10 to 15 mph after midnight. Gusts up to 30 mph Winds 20 to 30 mph. Gusts up to 45 mph increasing to 60 mph in the afternoon
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.