THIS AVALANCHE ADVISORY EXPIRED ON February 24, 2018 @ 7:19 am
Avalanche Advisory published on February 23, 2018 @ 7:19 am
Issued by Dave Bingaman - Payette Avalanche Center
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Human triggered avalanches are possible today where isolated wind slabs may be found on upper and middle elevation, wind exposed slopes.  The new snow we received this week may be hiding older wind slabs left from last week's strong winds.  Loose snow avalanches are likely on slopes over 35 degrees.  Numerous natural and human caused avalanches occurred in the last 6 days, most of these failed in wind loaded areas where faceted snow was resting on a stout crust below.

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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Strong winds and 16-21 inches of new snow have created a recipe for slab avalanches throughout the West Central Mountains over the last week.  Winds have swirled around from the S to the NE during this time creating wind slabs on multiple aspects.  The newest crop of wind slabs is in the 10-14 inch range with older wind slabs as deep as 2.5 feet possible.  Some of these wind slabs from last week are now camouflaged by the addition of new snow above them.  A layer of faceted snow developed in some areas prior to the last 8 days of storms and is resting on the stout crust deposited in late January allowing avalanches in these areas to propagate over larger areas.   These slabs while widespread are not reactive in all areas, your best bet for triggering a shallow or deeper slab is going to be found on steep, NW, N and NE terrain.  In addition, E and W aspects may be harboring isolated wind slabs on cross loaded slopes and smaller terrain features.

Winds are currently gusting out of the NE to near 20 mph and another significant storm will be entering the area beginning tonight. Pay attention to changing conditions, fluctuations in the temperature over the next few days and the addition of 16- 30 inches of new snow over the next 3 days.

Watch for signs of instability today and through the weekend including:  recent avalanche activity, cracking, collapsing and whumphing in the snowpack.  If you encounter these or signs of denser snow resting on the light snow below, stick to lower angle, less avalanche prone terrain.

See photos below for big wind features where North winds pushed snow up a gully into this pyramid  feature on a flat ridge and cracking in the upper 14 inches of the snowpack on a small wind slab.

                                

Avalanche Problem 2: Loose Dry
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Loose, dry avalanches or sluffs are widespread right now on steep terrain.  Our mountains have received between 16 and 21 inches of new, low density snow over the last 7 days. Widespread natural sluffing and point releases in the light density snow are visible on multiple aspects and on steep terrain at all elevations.  While these small avalanches don't pack a lot of punch, they do have the ability to pile up in terrain traps or steer a skier where they don't want to go.  Use good travel etiquette and keep your eyes on your partners.  Avoid steep, confined and consequential terrain where a small sluff could create larger problems.  Additional storm and wind deposited snow will continue to add to this problem over the next few days.

advisory discussion

Please come out and support the FPAC tonight at the McCall Golf Course.  Fundraiser and music starts at 7pm.  Raffle throughout the evening.  Also, PLEASE take the time to send us your observations of the snowpack or avalanche activity.  Several incidents occurred this week and went unreported to the PAC.  It's easy to do, it takes just a few minutes and it may save a life.  Click on the send observations tab on the advisory page or on the main menu.  See you at the Fundaiser tonight!

 

recent observations

Yesterday we toured near Fisher Creek Saddle and found great, possibly the best skiing and riding conditions of the season.  We also saw signs of widespread sluffing on steeper terrain and the remnants of natural avalanches that have occurred over the last week.  Winds have been able to move the new snow around in some unusual ways over the last week creating not only a variety of wind slabs but some fairly large cornices, and  wind spines in the upper elevation terrain.  Pit tests in northerly, high elevation terrain showed 10-16 inches of very low density snow resting on a more dense layer which is resting on a decomposing crust.  Above the crust is a layer of rounding but  still loose and faceted snow that formed in some areas prior to last week's storms.  This layer failed in both compression and propagation tests at an hard moderate or low considerable level. 

Several natural and human triggered avalanches in the 2 foot range failed at this layer earlier in the week or on the crust below.  The largest reported avalanche was in Wildwood Bowl just outside the north boundary of Tamarack Resort and prompted a beacon and dog search by Tamarack Ski Patrol after getting reports that it was skier triggered and witnesses hearing shouts for help.  Also, our condolences and thoughts  go out to the family of a snowmobiler from Idaho Falls that was killed Wednesday in eastern Idaho in an avalanche near Pallisades Falls.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: -2 deg. F.
Max. temperature in the last 24 hours: 21 deg. F.
Average wind direction during the last 24 hours: N
Average wind speed during the last 24 hours: 5 mph
Maximum wind gust in the last 24 hours: 18 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: 73 inches
Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: Partly sunny, with a high near 22. Wind chill values between -4 and 6. Light and variable wind becoming west around 5 mph in the afternoon. A 50 percent chance of snow. Cloudy, with a low around 11. West southwest wind around 6 mph becoming south after midnight. New snow accumulation of 1 to 2 inches possible. Snow. Areas of blowing snow. High near 25. South wind 6 to 11 mph becoming west in the afternoon. Chance of precipitation is 90%. New snow accumulation of 2 to 4 inches possible.
Temperatures: 22 deg. F. 11 deg. F. 25 deg. F.
Wind direction: W W S
Wind speed: 5 6 6-11
Expected snowfall: 0 in. 1-2 in. 2-4 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Partly sunny, with a high near 11. Wind chill values between -6 and -16. North northeast wind 6 to 10 mph becoming west southwest in the afternoon. Snow likely, mainly after 11pm. Areas of blowing snow after 11pm. Cloudy, with a low around 5. Wind chill values between -5 and -10. Southwest wind 9 to 11 mph. Chance of precipitation is 70%. New snow accumulation of 2 to 4 inches possible. Snow. Areas of blowing snow. High near 14. Wind chill values between -2 and -9. South southwest wind around 14 mph becoming west in the afternoon. Chance of precipitation is 100%. New snow accumulation of 4 to 8 inches possible.
Temperatures: 11 deg. F. 5 deg. F. 14 deg. F.
Wind direction: NNE SW SW
Wind speed: 6-10 9-11 14
Expected snowfall: 0 in. 2-4 in. 4-8 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.