THIS AVALANCHE ADVISORY EXPIRED ON December 24, 2016 @ 6:55 am
Avalanche Advisory published on December 23, 2016 @ 6:55 am
Issued by Dave Bingaman - Payette Avalanche Center
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The avalanche danger is Moderate above 6,000 feet. Below 6,000 feet, the avalanche danger is Low. Watch for wind slabs near ridgetops, and a widespread weak layer of facets near the bottom of the snowpack that has a 3-5 foot slab resting on it. Additional snowfall and wind beginning today and continuing through Christmas Eve will increase the avalanche hazard on upper elevation 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: Persistent Slab
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We have found a weak layer near the ground in multiple location over the last two weeks that is made up of weak faceted snow or a combination of facets and old crusts left over from our early season snowpack.  The weak layer of facets is fairly widespread and well developed in the upper elevations especially on the shadier aspects where early snowfall accumulated.  Shallow rocky areas are also harboring this layer on other aspects.  George described this problem earlier this week as a low probability/ high consequence avalanche problem...meaning you are not very likely to trigger a slide this deep but the consequences if you did would be bad.  The 3-5 foot overlying slab is gaining strength which is good but is also turning into more of a hard, consolidated meat grinder if it fails.  This is a good thing to keep in your mind if you are sidehilling and cutting in deep with your track on steep, shady terrain or exposed and shallow slopes with a lot of snow connected around you.  Use good travel techniques(one at a time) and watch your partners.

Avalanche Problem 2: Wind Slab
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We found small wind slabs and large wind drifts near the ridgetops on multiple aspects yesterday.  Over the last week we have experienced S/SW and N winds that have been sculpting and transporting the light density snow that has accompanied the last 2 storms.  Over the next 12-24 hours we will see winds at the upper elevations gusting into the 30mph range creating another round of wind slabs at or near the ridgelines.  Be aware of crossloaded areas on smaller terrain features and watch out for obvious clues like cracking or hollow sounding/feeling snow under your skis or track.

 

advisory discussion

 

There are a number of great beginner avalanche classes coming up for both skiers and snowmobilers. Be sure to check out 'local classes'  or upcoming events under the Education tab at the top of the forecast page. If you already have the basics down and are ready to take your Level One, skiers and snowmobilers can find classes this winter around the state, don't make excuses, just do it!  Make staying safe while playing in avalanche terrain a New Year's Resolution!

recent observations

We found blue skies and great snow conditions yesterday on our tour of Squaw Point with a fairly shallow snowpack compared to other locations through the Advisory area.  Gusty winds over the last week have left there mark near the ridgetops in the form of shallow wind slabs and large wind spines/drifts.  Our pit results showed this shallow snowpack was harboring the same layer of weak faceted snow near the ground on multiple aspects. While harder to trigger where it is buried more deeply on wind loaded aspects, we still had impressive failures at a density change in the upper pack as well as in the well developed basal facets near the ground.  The shallow and rocky South face failed at the ground with Moderate loading on a Compression Test on a layer of less developed basal facets.  You can easily see the differences in the snowpack in the photos below.

 

weather

Fog in the valleys will erode as winds associated with an approaching upper level trough brings gusty and snowy conditions to the West Central today.  Winds are forecasted to gust into the 30+mph range in the upper elevations with between 2-5 inches of snow in the valleys and 5-10 inches in mountain locations. Monday will bring mostly clear skies with another storm system entering the area by mid week.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: Snow Snow Snow
Temperatures: 24 deg. F. 24 deg. F. 28 deg. F.
Wind direction: South South/Southwest West/Northwest
Wind speed: 3-7 5 becoming calm 5-7
Expected snowfall: 1-3 in. 1-2 in. 1-2 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Snow Snow Snow
Temperatures: 24 deg. F. 25 deg. F. 22 deg. F.
Wind direction: South South South
Wind speed: 20-24 gusting to 33 7-17 8-13
Expected snowfall: 3-5 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.