THIS SNOWPACK SUMMARY EXPIRED ON January 9, 2019 @ 7:31 am
Snowpack Summary published on January 7, 2019 @ 7:31 am
Issued by Ryan Lewthwaite -

bottom line:

Keep it simple today. Stick to very low angle terrain or open meadows, not in a runout zone. Watch your partners closely & have a plan for avoiding avalanche terrain. Contol your powder lust & give the new snow time to find its secure place on the slopes, it could take days. News of a snowmobile collision fatality from the westside of Sonora Pass has us mourning; take care of each other out there. Please submit snowpack & avalanche observations, we need your input. An avalanche forecast bulletin board has been posted at the end of Virginia Lakes road, FYI.  

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 to Gale force winds have tossed the new snow around the mountains. Wind slabs will still be collecting snow throughout the day as SW winds persist. Shooting cracks were observed in flat terrain indicating dense slab formation & propigation of failures under skis. Aspects to be concerned with are NW-N-SE for the windslab problem. 

Avalanche Character 2: Storm Slab
Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.

With successive storms the load has not had time to sinter & all aspects are at risk of storm slab avalanches. The wind effected above treeline zone may have less of this problem but still be weary of protected & loaded terrain features.

Avalanche Character 3: 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.

Very large & still growing cornices are readily available for crushing failures. It is impossible to predict when an overhanging collection of wind-driven snow will collapse, just avoid them at all cost.

Snowpack Discussion

Evidence of avalanche activity was fully obscured by thick clouds in the alpine. There is no doubt that natural slides are flushing themselves with unfathomable fequency & intensity today. Strong to Gale force winds were transporting the new snow all day & forming soft to breakable slabs below treeline. Shooting cracks were noticed in isolated slabs while traveling on roads with snowmobiles. The large accumulations of new snow & wind have created instabilities in the storm snow that are widespread across the landscape. Avoid being in avalanche terrain!

recent observations

Travel on sleds yesterday was interesting & limited by new snow depth & underpowered machines. +16" of very low density snow was scattered around the mountains with irregularity by swirling strong winds. Low visibility meant seeing avalanche activity was nearly impossible. Snotel equipment has limited data due to no transmissions, solar panel covered by snow.

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 19 deg. F.
Max. temperature in the last 24 hours: 23 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: strong mph
Maximum wind gust in the last 24 hours: gale mph
New snowfall in the last 24 hours: +12 inches
Total snow depth: 38 inches
weather

Copius amounts of snow have fallen in the past 48 hours, elevating the avalanche danger. Winds predominantly from the SW were very strong & swirling yesterday, all the while transporting the low density snow everywhere. In my weather observation yesterday @ Sonora Snotel I recorded: Obscured sky, >+1" snow/hr, moderate NW/swirling winds & blowing snow, Tair -6.2C, Tsurf -5.4C, precipitation particles with rime, Fpen 30cm, HS 95cm, HN24 32, HST +32, elevation 8770' 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Monday Monday Night Tuesday
Weather: Mostly cloudy with morning snow showers & a slight chance for afternoon snow showers Snow Levels 7000' Cloudy Snow Levels 7000' Cloudy with a chance for snow showers later Snow Levels 7500'
Temperatures: 30 to 35 deg. F. 25 to 31 deg. F. 34 to 39 deg. F.
Wind direction: Southwest South South
Wind speed: 30 to 45 mph; gusts to 85 mph decreasing to 15 to 30 mph; gusts to 60 mph later 10 to 15 mph; gusts to 45 mph decreasing to 30 mph late 10 to 15 mph; gusts to 30 mph increasing to 50 mph later
Expected snowfall: 2 in. 0 in. 0 in.
For above 10000 ft.
  Monday Monday Night Tuesday
Weather: Mostly cloudy with snow showers Snow Levels 7000' Cloudy Snow Levels 7500' Mostly cloudy with a chance for snow showers later Snow Levels 8000'
Temperatures: 24 to 29 deg. F. 20 to 25 deg. F. 29 to 34 deg. F.
Wind direction: Southwest South South
Wind speed: 45 to 65 mph; gusts to 110 mph decreasing to 30 to 45 mph; gusts to 70 mph later 15 to 30 mph; gusts to 55 mph decreasing to 40 mph late 15 to 25 mph; gusts to 40 mph increasing to 25 to 40 mph; gusts to 60 mph later
Expected snowfall: 2 to 4 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.