THIS AVALANCHE ADVISORY EXPIRED ON February 1, 2016 @ 6:34 am
Avalanche Advisory published on January 31, 2016 @ 6:34 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Danger is Moderate today in most areas. The exception is 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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Wind slabs continue to be a problem in the upper or wind exposed middle elevations, especially in the Southern portion of our advisory area. With the new snow and wind over the last 48 hours, expect to find fresh wind slabs on north, northeast, northwest and crossloaded west and east aspects. You are most likely to find these slabs at or near the ridgetops or in exposed terrain above 7,000 feet. They are still relatively widespread in the upper elevations and range in sensitivity from easily triggerable to resistant. 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, some of these wind slabs may be resting on a new layer of buried surface hoar that was formed early last week. We saw a 8-12 inch, moderately hard windslab that was fairly reactive to ski cuts yesterday throughout the Tamarack back country.

Avalanche Problem 2: Persistent Slab
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While we are still thinking about and looking for the older buried surface hoar layer that is now proving to me mostly non-reactive or has been crushed in most areas, we now have a new crop of preserved surface hoar that was buried under this week's new snow.  We found this new layer to be obvious in our pits and reactive in our tests yesterday in the West Mountain area.  Slightly higher temperatures during the Thursday/Friday Storm resulting in a fairly dense slab overlying the Surface Hoar in the Southern portion of the valley have made this our next layer of concern.  We were able to initiate failure on this layer with Low Compression Test scores yesterday and also had full block propagation in our ECT test at 12 loading steps.  Both of these layers merit concern in protected, northerly terrain and are going to be more reactive to the weight of a skier or snowmobile right now than the snow in other areas. Use caution  and good travel protocols if you are riding or sliding in this kind of 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 it on slopes before committing to any slope steep enough to slide.  We will be out  tomorrow in the Northern portion of the advisory area looking for this layer there as well.  

advisory discussion

Our condolences go out to the families and friends of the 5 snowmobilers killed Friday in BC.  Early reports say 13 people were injured in one large avalanche with 5 fatalities. Canadian avalanche forecasters were on scene conducting an investigation yesterday but have not released their findings yet.  http://www.cnn.com/2016/01/30/americas/canada-avalanche/

 

recent observations

We took our Lift Access Backcountry class out into the Tamarack Back Country yesterday and found some surprisingly touchy snow in the windloaded northerly aspects. Our Compression Test scores were in the 8-10 range with an ECT that propagated full block at 12 Q1/SC. These tests failed on a new layer of preserved surface hoar at 35 cm.  The snow in the South Valley area seems quite a bit more dense as temperatures were slightly warmer in this area when the snow came in on Friday. The resulting slab above the weak layer was a dense combination of windslab and heavy/dense new snow resting on lower density snow below...not a good combination. Tamarack Ski Patrol also reported a skier triggered slide on the South side of the resort that left a skier at least partially buried and with a tweaked knee after tangling with the heavy debris. We were shocked at how many skiers and boarders were accessing this terrain under CONSIDERABLE danger without any rescue gear, remember this area is not part of the resort, has no avalanche control work and rescue by the Ski Patrol is not a given.  On the flip side, reports from the Northern half of the advisory area reported better bonding, less Buried Surface Hoar and a lower density windslab problem. George was out in the area near Goose Lake and reported better bonding in the new snow layers and overall better ski conditions than what we saw down South.

weather

Look for scattered snow showers over the next few days with cooler temperatures. Light accumulations will be possible through the next few days with temperatures staying below normal. Winds today will be in moderate out of the West switching to the North as a cold front moves into the area.  Cold northerly winds will drive wind chills down into the 0 degree range tonight and tomorrow.  Another storm will be entering the West Central Thursday, until then cooler temps and light accumulations are forecasted each day.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: Isolated snow showers after 11am. Patchy fog before 11am. Otherwise, partly sunny, with a high near 27. Light and variable wind. Chance of precipitation is 20%. Mostly cloudy, with a low around 3. Wind chill values between -9 and 1. Light and variable wind becoming northeast 5 to 7 mph in the evening. A 20 percent chance of snow showers after 11am. Mostly cloudy, with a high near 24. Wind chill values between -3 and 7. Northeast wind around 6 mph becoming light and variable.
Temperatures: 27 deg. F. 3 deg. F. 24 deg. F.
Wind direction: variable NE NE to variable
Wind speed: light 5-7 up to 6
Expected snowfall: trace in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: Scattered snow showers after 11am. Mostly cloudy, with a high near 23. West northwest wind around 5 mph becoming calm in the morning. Chance of precipitation is 30%. Total daytime snow accumulation of less than a half inch possible. A 20 percent chance of snow showers before 11pm. Mostly cloudy, with a low around 11. Wind chill values between -4 and 6. North northeast wind 9 to 13 mph. A 30 percent chance of snow showers, mainly after 11am. Mostly cloudy, with a high near 21. Wind chill values between -3 and 7. North wind 9 to 11 mph. New snow accumulation of less than a half inch possible.
Temperatures: 23 deg. F. 11 deg. F. 21 deg. F.
Wind direction: W/NW N/NE N
Wind speed: 5 becoming calm 9-13 9-11
Expected snowfall: Trace in. 0 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.