THIS AVALANCHE ADVISORY EXPIRED ON February 3, 2016 @ 7:08 am
Avalanche Advisory published on February 2, 2016 @ 7:08 am
Issued by George Halcom - Payette Avalanche Center
bottom line

The Avalanche Danger is Moderate today. Exercise caution in wind loaded terrain above 7000 feet, especially in the Southern Half of our advisory area and throughout the West Mountain area.  In these areas human triggered avalanches are more likely on windloaded slopes over 30 degrees, and protected slopes where the Surface Hoar layer was preserved below the new snow. Moderate Danger means heightened avalanche danger on specific terrain features, careful snowpack and terrain evaluation is essential.

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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Fresh wind slabs remain our primary concern today. With the new snow and wind on Friday expect to find wind slabs on north, northeast, northwest and cross loaded west and east aspects. You are most likely to find these slabs at or near the ridge tops or in exposed terrain above 7,000 feet. They are still relatively widespread in the upper and middle elevations and range in sensitivity from touchy to unreactive. Shallow wind slabs are more likely right now but you may also find some deeper ones still lingering under a layer of new snow. These slabs range in density between soft to hard, which means they may let you get well out onto them before they fail. Also, keep in mind that some of these wind slabs may be resting on a new layer of buried surface hoar that was formed early last week, or even worse could step down to buried surface hoar that formed in early January.

Avalanche Problem 2: Persistent Slab
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Unfortunately our buried surface hoar will not go away quickly...it will persist,but has gained strenghth, and when it fails it can propigate, and the results can be big as we saw Sunday when a snomobiler was caught and buried fatally in a slide on this layer above Twin Lakes on Granite Mtn. We believe that the slide may have been triggered from a thin spot on the slab, where the weight of a snomobile penetrated the weak layer. Use caution and good travel protocols if you are skiing and riding in avalanche terrain.  These buried surface hoar layers have the potential to spread out or propagate over large areas when triggered and are the type of layer responsible for the majority of avalanche incidents and fatalities. Take the time to look for buried surface hoar on slopes before committing to any terrain steep enough to slide. If you are unsure, stick to slopes less than 30 degrees.

advisory discussion

 

 

recent observations

Yesterday, we were quite humbled when we went out to Twin lakes to investigate an avalanche that unfortunately claimed the life of a snomobiler from Lewiston on Sunday afternoon. We are still waiting on the details of how the slide was triggered? We looked at the crown, and the flanks of the avalanche and have verified that the slide failed on our buried surface hoar layer (persistent slab) about 2 1/2 feet down, which has been one of our avalanche problems that is lingering in random locations in our mountains, where it was protected from the wind. The buried surface hoar layer is getting deeper, stronger, and harder to trigger, but when triggered has the potential to propagate. We believe that this slide may have been triggered from a thin spot on the slab where fracture initiation was much easier as the slab varies in thickness. 

Our deepest sympaties go out to the friends and families...

 

weather

Today, we will see mostly cloudy skies with warmer temperatures than yesterday, a high near 24 degrees in the upper elevations with West winds around 3-5 MPH. 

 

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy, with a high near 26. Calm wind. Mostly cloudy, with a low around 6. Calm wind. A 20 percent chance of snow after 11am. Mostly cloudy, with a high near 26. Calm wind becoming south around 6 mph in the afternoon.
Temperatures: High 26 deg. F. Low 6 deg. F. High 26 deg. F.
Wind direction: Calm South
Wind speed: Calm Calm 6
Expected snowfall: 0 in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy, with a high near 24. Wind chill values between -1 and 9. West wind 3 to 5 mph. Mostly cloudy, with a low around 10. Wind chill values between -1 and 4. West northwest wind 5 to 7 mph. A 20 percent chance of snow after 11am. Mostly cloudy, with a high near 26. Wind chill values between -3 and 7. South southwest wind 8 to 16 mph, with gusts as high as 25 mph.
Temperatures: High 24 deg. F. Low 10 deg. F. High 26 deg. F.
Wind direction: West West Northwest South southwest
Wind speed: 3-5 5-7 8-16 with Gusts to 25 MPH
Expected snowfall: 0 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.