THIS SNOWPACK SUMMARY EXPIRED ON February 22, 2021 @ 8:27 am
Snowpack Summary published on February 20, 2021 @ 8:27 am
Issued by Jason Mozol - Bridgeport Avalanche Center

bottom line:

A couple inches of fresh snow overnight combined with strong winds shifting from SW to NW will create sensitive, small wind slab avalanches today. These will be found on N-E-S facing slopes, specifically in areas prone to wind loading at middle and upper elevations. These wind loaded areas will appear smooth and rounded. Look out for signs of instability, like cracking and collapsing. These avalanches may be small, but could be especially hazardous in extreme terrain. Also be aware of the variable snow conditions under the fresh snow, and the potential for small loose wet avalanches on southerly slopes Sunday. 

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.

Weather stations have picked up 2-4 inches of snow this morning and there is the potential for another couple of inches before the storm tapers off. This new snowfall is coming in with strong SW winds that will shift to NW through the day. These winds are drifting the snow into small wind slabs on N-E-S aspects, specifically in wind loaded areas at middle and upper elevations. Wind loaded areas can be significantly deeper than surrounding areas and appear smooth and rounded and may feel slabby and hollow. Look out for them in gullies, on steep rolls and under cornices. While traveling in the backcountry today, be on the lookout for signs of instability like cracking and collapsing. These are obvious red flags that the slope is unstable. While they may be small, these fresh wind slab avalanches will be especially hazardous in extreme terrain today. Remember that you can move to wind protected or wind scoured slopes to avoid the hazard.  

Last weekend, a couple of small storms with strong SW-W winds built wind slabs on lee aspects. These instabilities are stubborn but still lingering. It remains possible for you to trigger an older wind slab that breaks deeper than the most recent snowfall. Recent reports of these avalanches have died down, but yesterday we observed propagating test results on a density change in the upper snowpack.  

Snowpack Discussion

With sunny, warm, and calm weather forecasted for Sunday and Monday, be on the lookout for small loose wet avalanches on sunny southerly aspects. These loose wet avalanches should be mostly confined to the new snow, so areas that receive more snow today will be more susceptible and problematic tomorrow. Look out for rollerballs and other signs of instability. These avalanches will be small, but large enough to knock you off your feet, making them especially hazardous in extreme terrain. 

Snow conditions are currently very variable in the backcountry. Under the couple of inches of fresh snow that fell last night and this morning, you can find a mix of wind, sun, and rain crusts of varying stiffnesses. Be cognizant of these difficult conditions as you head out into the backcountry. Unfortunately, the most appealing steep terrain to ride today will be the same places you might find a wind slab. While out looking for good snow, remember that you could trigger a wind slab in wind loaded terrain. 

The weak layer of facets at the bottom of our snowpack is no longer one of our primary concerns, but we are still tracking it. These facets are found on NW-N-E aspects at middle and upper elevations and are generally buried 1+ meter deep by a stiff slab of snow. While out in the BWRA yesterday we measured the snow depth across the slope of a NE aspect around 10,300 feet. The snow depth was surprisingly variable, changing from 50 cm up to 250 cm over a short distance with little evidence of the change present at the snow surface. The shallow areas still had facets at the ground, and represented potential trigger points for deep persistent slab avalanches. In the shallow spots, your weight could be enough to collapse the weak facets and trigger an avalanche that breaks across the whole slope. That being said, these basal facets have been unreactive in snowpit tests recently and we have not received any reports of recent avalanches on the facets. If you found just the right spot, you could potentially trigger one of these avalanches, but it is highly unlikely.  

recent observations

2-4 inches of new snow and strong SW winds overnight and this morning.  

Variable snow surface conditions are present in the backcountry with a variety of hard and breakable crusts from recent sun, wind, and warm temperatures.  

Unreactive basal facets are buried 3+ feet deep on NW-N-E aspects at middle and upper elevations. 

CURRENT CONDITIONS Weather observations from Sonora Pass
0600 temperature: 14 deg. F.
Max. temperature in the last 24 hours: 33 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 25-35 mph
Maximum wind gust in the last 24 hours: 70 mph
New snowfall in the last 24 hours: 2-4 inches
Total snow depth: 98 inches

We could see a couple more inches of snowfall this morning before a quick hitting storm moves out during the day today. Temperatures will be colder today and winds will remain elevated. Skies will turn partly cloudy by the afternoon. Sunday and Monday should be warmer, mostly sunny, and relatively calm. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8000 ft. to 10000 ft.
  Saturday Saturday Night Sunday
Weather: Mostly cloudy then becoming partly cloudy. Snow tapering to isolated snow showers by mid morning. Partly cloudy then becoming clear. Sunny.
Temperatures: 20 to 30 deg. F. 9 to 15 deg. F. 31 to 37 deg. F.
Wind direction: Northwest North Northwest
Wind speed: 15 to 35 mph with gusts to 60 mph. Around 15 mph in the evening becoming light. Gusts up to 40 mph. Light winds.
Expected snowfall: 50% probability 2 to 4 in. 50% probability up to 2 in. 0 in. 0 in.
For above 10000 ft.
  Saturday Saturday Night Sunday
Weather: Mostly cloudy then becoming partly cloudy. Snow tapering to isolated snow showers by mid morning. Partly cloudy then becoming clear. Sunny
Temperatures: 13 to 18 deg. F. 3 to 8 deg. F. 25 to 30 deg. F.
Wind direction: West to Northwest North Northwest to North
Wind speed: 45 to 60 mph with gusts to 105 mph becoming northwest and decreasing to 30 to 45 mph with gusts to 75 mph in the afternoon. 20 to 35 mph. Gusts up to 55 mph decreasing to 45 mph after midnight. 20 to 30 mph with gusts to 45 mph shifting to the north 15 to 20 mph with gusts to 30 mph in the afternoon.
Expected snowfall: 50% probability 2 to 4 in. 50% probability up to 2 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.