THIS SNOWPACK SUMMARY EXPIRED ON January 28, 2021 @ 8:31 am
Snowpack Summary published on January 27, 2021 @ 8:31 am
Issued by Jason Mozol - Bridgeport Avalanche Center

bottom line:

Very dangerous avalanche conditions exist today due to a powerful snowstorm impacting the region. Natural and human triggered avalanches are almost certain and will be widespread. Avoid traveling in or underneath avalanche terrain today. 

US 395 is currently closed from Mammoth Lakes to the Nevada state line at Topaz. It may or may not open today. The BWRA remains closed, but this storm should finally give us enough snow to be able to open. We are all excited to get it open and we will do so as soon as we are able to. The road to Virginia Lakes is likely now snowed-in.

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.

Extreme southerly winds are depositing today’s very heavy snowfall into widespread wind slabs. These avalanches will be touchy and prone to occur naturally. The winds are strong enough that they may be found in unusual locations on all aspects and elevations. These avalanches could be several feet deep and will likely increase in size as snow continues to fall throughout the day. They could run far into lower angled slopes you normally consider safe. Avoid traveling in or below avalanche terrain today where avalanches will easily be big enough to bury you.

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.

Very high snowfall rates of up to 4-5”+ per hour are creating touchy storm slabs at lower elevations that see less wind. These avalanches will be found on all aspects and will occur both naturally and from human triggers. These avalanches will likely grow to be very large by the end of the day. Again, even lower angled slopes that are exposed to steeper slopes above are not safe today.

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 faceted snow exists at the bottom of our snowpack on northerly slopes. The weak snow was beginning to heal before this storm but heavy snowfall today will add a significant enough load to potentially reactivate these layers. These avalanches are hard to predict and often surprise experienced backcountry travellers. They could propagate widely and be remotely triggered from below or adjacent to the slope. Today, persistent slabs could be triggered by smaller avalanches that step down to deeper weak layers. Any avalanche that fails on these layers would be very large and potentially run a long distance. Avoid traveling in or below avalanche terrain today.

Snowpack Discussion

Today is a day to take a step back. We are all excited to finally receive a significant snowstorm, but we need to acknowledge that it has brought dangerous avalanche conditions in the backcountry. We can’t let our powder-starved excitement get in the way of good decision making. Widespread avalanches are almost certain today and travelling in or below avalanche terrain is not recommended. Avalanche terrain means any slope steeper than 30 degrees including low angle slopes below. Heavy snowfall will continue through Friday morning and the avalanche conditions may be even more dangerous tomorrow. 

On many slopes today’s snow is falling on bare ground so also be aware of thin conditions and hidden obstacles. Hopefully these hazards will be fully buried tomorrow.

recent observations

Today’s very heavy snowfall and strong to extreme winds point to widespread instabilities. 

Before this storm 3-5 inches of low density snow rested on a highly variable old snow surface with stout crusts on southerlies and a mixed bag of breaker crusts, near surface facets, and wind board on northerlies.

Depth hoar exists at the ground on W-N-E aspects.

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 19 deg. F.
Max. temperature in the last 24 hours: 21 deg. F.
Average wind direction during the last 24 hours: S
Average wind speed during the last 24 hours: 35-45 mph
Maximum wind gust in the last 24 hours: 67 mph
New snowfall in the last 24 hours: 12-24 inches
Total snow depth: 54 inches
weather

Blizzard warning until 4 AM Friday. A powerful atmospheric river event will continue to bring us heavy snowfall and strong to extreme winds through Friday morning. Snowfall will be measured in feet and by Friday morning we may see over 6 feet of accumulation in the mountains.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Cloudy. Snow. Cloudy. Snow. Cloudy. Snow.
Temperatures: 20 to 26 deg. F. 18-24 deg. F. 22-28 deg. F.
Wind direction: South South South
Wind speed: South 25 to 40 mph with gusts to 95 mph decreasing to 20 to 30 mph with gusts to 75 mph in the afternoon. South 15 to 25 mph with gusts to 60 mph. South 15 to 25 mph. Gusts up to 55 mph decreasing to 45 mph in the afternoon.
Expected snowfall: 70% probability of 21 to 29 inches. 30% probability of 12 to 20 in. 80% probability of 16 to 24 inches. 20% probability of 10 to 16 in. 80% probability of 10 to 18 inches. 20% probability of 15 to 20 in.
For above 10000 ft.
  Wednesday Wednesday Night Thursday
Weather: Cloudy. Snow. Cloudy. Snow. Cloudy. Snow.
Temperatures: 14-20 deg. F. 11-16 deg. F. 15-21 deg. F.
Wind direction: South South South
Wind speed: South 45 to 65 mph with gusts to 115 mph decreasing to 35 to 55 mph with gusts to 95 mph in the afternoon. South 30 to 45 mph with gusts to 75 mph. South 35 to 50 mph decreasing to 20 to 30 mph in the afternoon. Gusts up to 75 mph.
Expected snowfall: 70% probability of 25 to 33 inches. 30% probability of 12 to 20 in. 80% probability of 19 to 27 inches. 20% probability of 10 to 18 in. 80% probability of 12 to 20 inches. 20% probability of 15 to 20 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.