THIS AVALANCHE ADVISORY EXPIRED ON February 18, 2018 @ 7:02 am
Avalanche Advisory published on February 17, 2018 @ 7:02 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

Conditions are changing in the mountains right now and you will need to change your mindset to match the conditions.  A combination of light density snow, wind and rising temperatures will elevate the avalanche hazard today.  Moderate to high W/SW winds hammered the upper elevations yesterday forming sensitive wind slabs on leeward slopes.  Slopes protected from the wind will be prone to loose, dry avalanches.   As temperatures rise today storm slabs will become a problem on all protected slopes.

 

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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Wind and wind slabs are going to be the major concern today in the upper elevations. The NWS forecast is calling for an additional 4-8 inches of snow possible with Southwest winds increasing to 19-24 mph and gusts over 30 mph.  An additional 4-8 inches of snow tonight and winds gusting to near 40 mph will continue to elevate the wind slab problem and increase the depth of the slab.

West and Southwest winds hit the West Central Mountains yesterday and had plenty of light density snow to transport.  Throughout the day yesterday on the high ridges near Diamond Rock we observed cornices growing and becoming very sensitive to the weight of a skier.  We also observed wind slabs growing in thickness and density through the day with gusts in the 25-30 mph range.  This problem should be mostly confined to North and East facing slopes BUT given smaller terrain features and undulations, you should expect wind slabs on any terrain with a North or East facing tilt, including gullies, small bowls and other natural catcher mitt features.  These slabs are resting on a slick crust in some areas and will propagate and move quickly if triggered. As winds pick up later in the day, expect the wind slab hazard to rise as well.

Avalanche Problem 2: Loose Dry
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On slopes over 35 degrees, Loose/Dry avalanches or Sluffs are a given today.  Sluffs are an indicator of great ski and riding conditions but can also push you around especially in treed, or confined terrain.  Below all of the new snow is a stout and in some areas slick crust which the new snow is not bonding to. Be extra careful if your line involves terrain traps such as benches or gullies where a little bit of moving snow can pile up quickly. 

Avoid traveling above your companions in steep terrain and keep your group corralled today; good travel practices, group and slope management as well as keeping eyes on all members of your group in steep terrain should be priorities.

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Avalanche Problem 3: Storm Slab
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With more than a foot of light density, cold snow already on the crust and old snow layers below, the addition over the next 24 hours of another 8-16 inches of warmer higher density snow will help form a storm slab in the new snow.  Rising temperatures today ahead of tomorrow's cold front will create a layer of more dense snow  and will be resting on the low density snow below which will make storm slab avalanches of between 1 and 2 feet more possible through the day today, overnight and into the day tomorrow.  This will be more likely in the middle and lower elevations where the temperatures will be close to 30 today.

advisory discussion

Don't forget about the FPAC fundraiser at the McCall Golf Course next Friday 2/23 at 7pm.  Admission includes raffle ticket with over $1000 worth of cool stuff, music by local bluegrass band Jughandle Parade and a short state of the snowpack address by the PAC staff.

Our website just went through a routine update and our email server is currently offline.  No advisory emails will be sent out today or tomorrow.  We are sorry for the inconvienience.  The problem should be resolved by early next week.

recent observations

Yesterday we toured into the Summit Lake and Diamond Rock area.  We found 8 to 15 inches of low-density snow sitting on top of a variable crust that formed during the last two weeks of warm day time temperatures (see video).   The new dry snow sluffed easily on steep terrain especially on sun affected slopes where the crust was more pronounced.  Below the surface, several melt/freeze layers exist in the upper snowpack but snow stability tests indicated that these layers are fairly strong.   

Winds are the game changer right now, yesterday strong SW and W winds were hammering the upper elevation terrain and moving snow easily into leeward slopes, South and West slopes took a beating and quickly formed a strong wind board or exposed the old crust below.  Cornices were growing rapidly and were very sensitive to the approaching weight of a skier.  Wind slabs were forming yesterday morning and grew from a thin shallow problem to a stiff, punchy slab between 4 and 12 inches thick.  By the end of the afternoon yesterday we were experiencing shooting cracks on wind pillows and steep rollovers.

The combination of wind and a high temperature in the  low teens yesterday kept us moving and made staying warm a priority so videos and photos were not the priority.  We will try to get some form of media on tomorrow's advisory.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 17 deg. F.
Max. temperature in the last 24 hours: 17 deg. F.
Average wind direction during the last 24 hours: W
Average wind speed during the last 24 hours: 10 mph
Maximum wind gust in the last 24 hours: 19 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: 64 inches
Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Snow. High near 24. Wind chill values between -1 and 5. Breezy, with a south southwest wind 11 to 16 mph increasing to 19 to 24 mph in the afternoon. Winds could gust as high as 33 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 4 to 8 inches possible. Snow. Low around 15. Breezy, with a southwest wind 23 to 28 mph decreasing to 16 to 21 mph after midnight. Winds could gust as high as 38 mph. Chance of precipitation is 100%. New snow accumulation of 4 to 8 inches possible. Snow showers. High near 17. Wind chill values between -1 and 4. Southwest wind 11 to 13 mph. Chance of precipitation is 80%. New snow accumulation of 2 to 4 inches possible.
Temperatures: 24 deg. F. 15 deg. F. 17 deg. F.
Wind direction: SW SW SW
Wind speed: increasing to 19-24, gusts to 33 23-28, gusts to 38 11-13
Expected snowfall: 4-8 in. 4-8 in. 2-4 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Snow. High near 35. South wind 5 to 14 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 2 to 4 inches possible. Snow. Low around 23. South southwest wind 8 to 16 mph. Chance of precipitation is 100%. New snow accumulation of 1 to 2 inches possible. Snow showers likely. Cloudy, with a high near 29. West southwest wind 7 to 9 mph. Chance of precipitation is 60%. New snow accumulation of less than one inch possible
Temperatures: 35 deg. F. 23 deg. F. 29 deg. F.
Wind direction: S SW WSW
Wind speed: 5-14 8-16 7-9
Expected snowfall: 2-4 in. 1-2 in. 1 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.