THIS AVALANCHE ADVISORY EXPIRED ON February 21, 2016 @ 7:10 am
Avalanche Advisory published on February 20, 2016 @ 7:10 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The avalanche danger is CONSIDERABLE in steep, windloaded terrain. 12-16 inches of snow fell over the last 48 hours with strong winds forming dense windslabs on leeward slopes. Human triggered avalanches are likely on steep, windloaded slopes. In steep, sheltered terrain, loose snow and storm slab avalanches are possible  SE, S and SW aspects are harboring slick, buried sun crusts which the new snow is not bonding to. Below 7000 feet the avalanche danger is MODERATE in wind protected terrain.

 

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 have been hammering the West Central for the last 3 days. Wind gusts have been in the 40-60 range on the higher peaks and ridges with sustained winds in the 20+range.  Tamarack Resort clocked wind speeds in excess of 40 mph for a large portion of the day on Thursday.  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.  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.

 

 

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.  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 cant 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.  

advisory discussion

Thanks to everyone that came out for last night's backcountry film festival. Great crowd, cool flix!  Proceeds benefited the FPAC and the McCall Winter Sports Club.

recent observations

We traveled in the Fisher and Little French Creek Drainages yesterday and found wind affected snow on multiple aspects.  Strong South winds were hammering the mountains and the snowpack throughout most of the day. The result was very stiff windboard( hard snow) on  South and East Aspects with large drifts growing across the fall lines on the East aspects.  On the Northerly terrain, we found a mix of stiff windslab and relatively soft windslab ranging in depth from a few inches to over a foot thick.  The top layer was reactive to ski cuts and small cornice bombs and once we got off the ridges it skied well.  The best snow is lower down in protected areas and down low in the northerly terrain. In addition on lower elevation steep slopes we found plenty of soft snow(dry/loose avalanches) moving around as we skied through short steep sections.  The photo below shows the wind affect on a West facing slope near Fisher Saddle.  Note the scalloped shaped drifts across the slope.

weather

The NWS forecast is calling for scattered snow showers today throughout the West Central Mountains.  A few more weak pulses of precipitation will move through Sunday night and into early next week.  Temperatures are expected to be a few degrees above average and will continue climbing through the week next week. The snowline will hover between 3000 and 5000 feet with the precipitation on Sunday night. Winds will be generally light out of the Southwest over the next few days.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Scattered snow showers before 11am. Mostly cloudy, with a high near 32. South southwest wind 3 to 5 mph. Chance of precipitation is 30%. Total daytime snow accumulation of less than a half inch possible. Mostly cloudy, with a low around 15. Calm wind. Partly sunny, with a high near 37. Light south wind.
Temperatures: 32 deg. F. 15 deg. F. 37 deg. F.
Wind direction: S/SW Calm South
Wind speed: 3-5 Calm Light
Expected snowfall: trace in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Scattered snow showers, mainly before 11am. Mostly cloudy, with a high near 28. Southwest wind 9 to 13 mph. Chance of precipitation is 40%. Total daytime snow accumulation of less than one inch possible. Mostly cloudy, with a low around 17. South wind 6 to 10 mph. Partly sunny, with a high near 35. South southwest wind 11 to 15 mph.
Temperatures: 28 deg. F. 17 deg. F. 35 deg. F.
Wind direction: S/SW South S/SW
Wind speed: 9-13 6-10 11-15
Expected snowfall: Trace in. 0 in. 0 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.