THIS AVALANCHE ADVISORY EXPIRED ON February 22, 2016 @ 6:46 am
Avalanche Advisory published on February 21, 2016 @ 6:46 am
Issued by Dave Bingaman - Payette Avalanche Center
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The avalanche danger is CONSIDERABLE in steep, upper elevation, windloaded terrain. New snow and strong winds last week formed dense windslabs on leeward slopes. Human triggered avalanches are possible on steep, windloaded slopes. In steep, sheltered terrain, loose snow and storm slab avalanches are possible. The Southerly aspects are harboring slick, buried sun crusts which the new snow is not bonding to. Warming temperatures today may create the possibility of wet/loose or point release slides on sunny aspects.

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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Winds out of the South, Southeast and Southwest hammered the West Central Mountains through the second half of last week. Wind gusts were in the 40-60 MPH range on the higher peaks and ridges with sustained winds in the 20+range. The avalanche danger on wind loaded upper elevation terrain is enough to merit conservative terrain choices on all wind affected slopes. These strong winds have done a great job loading and crossloading slopes on East, North and West facing aspects as well as loading slopes below rocky or steep headwalls well below the ridgetops.  Windslabs range from very stiff to soft today and from a few inches to over a foot thick. Some of these windslabs formed on the crusts that developed during our last high pressure. Look for clues like cracking and collapsing as well as other obvious signs of windslab like a textured or scalloped snow surface or pillows and drifts as you are moving through the mountains today.  Additional snowfall on Friday evening also did a great job camouflaging some of these obvious clues so pay attention to the way the snow feels as you travel today, if you encounter a hollow, punchy, or drummy feeling snow surface you are on windslab.  Snowmobiles may have more of an affect on these slabs than skiers where they are more dense or firm. Wind slabs often let you get well out on to them before you are able to trigger them trapping you in the middle of the slab when it is triggered. 

Avalanche Problem 2: Storm Slab
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After the 2 week high pressure we had a variety of old snow surfaces throughout the mountains.  The new snow over the last few days fell on slick crusts and melt freeze crusts as well as old wind slabs and some areas of faceted snow.  On most East and Northerly aspects the crust has already broken down or the wet snow at the beginning of the storm cycle is bonding to the old snow surface below.  South and West aspects are showing less bonding on a more stout and slicker crust.  Mid slab instabilities  within the new snow are also present and can be found easily if you do a quick hand shear test or take a couple of minutes to dig into the snow.  Several weak layers are present within this new storm slab. Quick tests like sled or ski cuts above a skin track or lower sled track will show you exactly how the new snow is bonding to itself.  Generally speaking, storm slab instablities settle out quickly as the new snow gains strength withough additional load. Also, on steeper slopes, expect dry loose avalanches or sluffs as the lighter density snow near the surface starts moving with you or your sled. Sluffs and storm slabs can quickly entrain more snow once triggered and can easily knock you off your skis or steer a skier or sledder into areas or features where they don't want to go.

Avalanche Problem 3: Deep Slab
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We are still finding, what will likely be a permanent fixture in our snowpack for the rest of the season: buried surface hoar. Triggering a slab due to this weak layer has become more difficult as the overlying snow continues to gain strength but we can't ignore it.  We are still finding this weak layer in upper elevation wind protected terrain. Pit results and stability testing point toward less likelihood of triggering, but if triggered we are still talking about a potentially unsurvivable hard slab avalanche. Take the time to carefully assess terrain choices on the north half of the compass today and throughout the rest of the season. This layer is especially dangerous in areas where the snow cover is thinner which allows the buried surface hoar to be closer to the surface, and in turn more reactive---especially for snowmachines. This is the same layer that was the cause of the fatal avalanche on January 31st. A persistent,deep weak layer such as this is a low probability, but HIGH CONSEQUENCE scenario.  

recent observations

Skiing and riding improved Saturday with a light dusting of new snow and cold temperatures Friday night.  We had a report of a decent sized Natural Avalanche near Marge Lake on Friday but didn't hear or see anything new activity yesterday.  If you do trigger or see avalanche activity, please take the time to send us a short report and a photo with as much of a description as possible.  You can email avalanche info to us at: forecast@payetteavalanche.org or plug it into our Observations page on the website . Your help is greatly appreciated!

weather

Look for partially cloudy skies today with a chance of light snow accumulations tonight and through Monday. By Tuesday the West Central will be under another ridge of high pressure with above average temperatures trending upwards through the week. Winds today will be in the low teens out of the Southwest and will begin to migrate around to the Northwest later tonight as a cold front moves through. There is another system in the Pacific that may affect our area beginning Friday.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: Increasing clouds, with a high near 37. Light south wind. A slight chance of rain and snow showers before 11pm, then a chance of snow showers. Cloudy, with a low around 22. Calm wind. Chance of precipitation is 30%. New snow accumulation of less than a half inch possible. A 20 percent chance of snow showers after 11am. Mostly cloudy, with a high near 35. Calm wind becoming west around 5 mph in the afternoon.
Temperatures: 37 deg. F. 22 deg. F. 35 deg. F.
Wind direction: South Calm West
Wind speed: Light Calm 5
Expected snowfall: 0 in. Trace in. Trace in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: Increasing clouds, with a high near 34. South southwest wind 11 to 13 mph. A 40 percent chance of snow showers. Cloudy, with a low around 20. Southwest wind 7 to 13 mph becoming west northwest after midnight. New snow accumulation of less than one inch possible. A 30 percent chance of snow showers after 11am. Mostly cloudy, with a high near 30. Northwest wind 6 to 10 mph. New snow accumulation of less than a half inch possible.
Temperatures: 34 deg. F. 20 deg. F. 30 deg. F.
Wind direction: S/SW W/NW NW
Wind speed: 11-13 7-13 6-10
Expected snowfall: 0 in. Trace in. Trace 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.