THIS AVALANCHE ADVISORY EXPIRED ON January 18, 2020 @ 7:34 am
Avalanche Advisory published on January 17, 2020 @ 7:34 am
Issued by Dave Bingaman - Payette Avalanche Center
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The Avalanche danger is Considerable in the upper elevations. Strong winds and light new snow have formed wind slabs on multiple aspects.  Expect storm slabs 8-12 inches that will also be sensitive to the weight of a skier or snowmobiler from last nights snowfall.  While the most sensitive snow lies in the upper snow pack, it remains possible to trigger an avalanche in older weak layers that are now buried 3-5 feet deep or more.

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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New wind slabs and storm slabs have continued to grow with winds gusting upwards of 35 mph yesterday and well into the 20's overnight.  Yesterday's winds started out SSE and marched around the compass overnight to NE.  Expect windslabs on multiple aspects today.  In general be cautious in the upper elevations and avoid wind loaded terrain.

Light density snow is easily transported by the wind and can result in widespread wind loading.  You are MOST likely to find wind slabs near ridge lines and on cross loaded slopes(think gullies and sub-ridges) in the upper elevations but today wind slabs and new storm slabs are going to be even more widespread.  Winds were whipping yesterday with pluming and blowing snow on every ridge and peak. We also observed some wind transport in the middle elevations as well so if you are are on steeper slopes or rollovers even at or below 7000 feet watch for changes in the snow surface.

Look for wind affected areas, notice changes in the density of the snow surface and recognize red flags like cracking or collapsing under your skis or sleds.  Cornices are also building and becoming brittle in some areas, avoid getting out on the edge of large cornices and pay attention to what is above you on the ridgelines.

Check out this short video of the wind at 8600 feet yesterday.

Avalanche Problem 2: Deep Slab
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We would really like to think that the 40+inches of new snow last week has decreased the potential for our old persistent weak layers but unfortunately there is still a lingering possibility of triggering them.  We had our first good visibility day out in quite a while and a saw fairly fresh crown from a large, natural avalanche that had failed all the way to these deep layers.  We dug a high elevation pit on a similar aspect and found a very deep layer of well preserved surface hoar(160 cm/62in down form the surface) and the rotten layer of snow above and below the crust nearly at the ground. which had 200cm/78in sitting above it.  While we generally don't worry about what is sitting at the bottom of a deep snowpack, the natural that we observed had at least a 6 foot crown and had cleaned the slope down to the rocks.  Wind loaded, upper elevation, rocky terrain where you have a non-uniform snow depth is the most likely type of area that these layers are still going to be triggered in, you are more likely to find a shallow trigger point that could propagate over a large area.  A slide like this would be very hard to survive.  Snowmobiles have been finding similar layers to our east and west with 2 fatalities over the last week.  Avoid steep, upper elevation northerly slopes unless you are feeling very lucky.

 

Natural avalanche crown on a windloaded, rocky NNW slope near 8400ft just soutwesth of Victor Saddle.  Estimated crown height 6+ft. Width approx 400 ft.

recent observations

Yesterday was a very intense day in the mountains.  We traveled up Diamond Ridge to take advantage of the good visibility and take a look at our high elevation snowpack.  DEEEP snow off trail made for an epic snowmobile approach with sled penetration around 3 feet, but surprisingly manageable even on our 600's.   Trail breaking was deep enough to make you sweat despite the single digit windchills until we hit the ridgelines which were scoured and wind hammered to about the same hardness as well cured cement.  Winds were the big story yesterday with 30mph winds whipping snow off of the open, burned ridgelines in every direction.  Windslabs and cornices were forming throughout the day on multiple aspects.

The snowpack grew by an amazing 80-100 cm over the last week and coverage is looking pretty good overall.  Most of the instability we found yesterday was confined to the upper 6-18 inches of the snowpack with several other older layers still popping off in clean fractures where density changes were noted.  Most notably, the old snow surface near 100cm down.  It broke in pit tests but did not have much energy (Sudden Collapse) on a layer of near surface facets.  at 8300 ft, this layer also had a dirty, brown tint that was visible when we excavated our pit.  Our pit also showed a very well preserved layer of surface hoar at 160cm and rounding but very loose basal facets above and below the November crust.  That structure was enough to keep us away from steeper terrain.  

    

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 9 deg. F.
Max. temperature in the last 24 hours: 25 deg. F.
Average wind direction during the last 24 hours: SW then NE
Average wind speed during the last 24 hours: 12 mph
Maximum wind gust in the last 24 hours: 36 mph
New snowfall in the last 24 hours: 3 inches
Total snow depth: NA inches
Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: A 30 percent chance of snow showers before 11am. Partly sunny, with a high near 25. West northwest wind around 6 mph becoming calm. Total daytime snow accumulation of less than a half inch possible. A 30 percent chance of snow, mainly after 11pm. Cloudy, with a low around 16. South wind around 5 mph becoming calm in the evening. New snow accumulation of 1 to 2 inches possible. Snow, mainly after 11am. High near 27. Calm wind becoming south around 6 mph in the afternoon. Chance of precipitation is 80%. New snow accumulation of 1 to 2 inches possible.
Temperatures: 25 deg. F. 16 deg. F. 27 deg. F.
Wind direction: W S S
Wind speed: 6 5 6
Expected snowfall: Trace in. 1-2 in. 1-2 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: A 30 percent chance of snow showers, mainly before 11am. Partly sunny, with a high near 13. Wind chill values between -2 and 5. Northwest wind 5 to 9 mph becoming light and variable. Total daytime snow accumulation of less than a half inch possible. A 50 percent chance of snow. Cloudy, with a temperature rising to around 16 by 2am. Wind chill values between -4 and 5. South southwest wind 8 to 10 mph. New snow accumulation of 2 to 4 inches possible. Snow, mainly after 11am. High near 19. South wind 9 to 18 mph. Chance of precipitation is 90%. New snow accumulation of 1 to 3 inches possible.
Temperatures: 13 deg. F. 16 deg. F. 19 deg. F.
Wind direction: NW S S
Wind speed: 5-9 8-10 9-18
Expected snowfall: Trace in. 2-4 in. 1-3 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.