THIS AVALANCHE ADVISORY EXPIRED ON January 12, 2020 @ 7:22 am
Avalanche Advisory published on January 11, 2020 @ 7:22 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

 A combination of wind slab and storm slab avalanches are likely on all steep terrain today.  Most of the hazard and the most sensitive snow lies in the upper snowpack, but you could trigger an avalanche in one of older weak layers that are now buried 2-4 feet deep.  These persistent layers are widespread throughout the area and will be getting a serious stability test with the weight of this storms snow.  Expect avalanche hazard to rise through the day.

How to read the advisory


  • Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
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New wind slabs are going to be your biggest concern today.  Light density snow is easily transported by the wind and can result in widespread windloading.  You are MOST likely to find windslabs near ridgelines and on crossloaded slopes(think gullies and sub-ridges) in the upper elevations but today windslabs and new storm slabs are going to be even more widespread.  A combination of new surface hoar growth mid week, light density snow from Wednesday and Thursday and over a foot of new snow will create some very touchy conditions on all steep slopes today.   We received widespread reports of new snow instabilities yesterday and we have added another 8-10 inches in the lower elevations.  Gusty South and Southwest winds combined with heavy precipitation intervals through the day will INCREASE the avalanche danger and increase your potential to trigger avalanches. 

Look for wind affected areas, notice changes in the density of the snow surface and recognize red flags like cracking or collapsing under your skis or sleds.  Today is the day to use good travel protocols, do not put more than one person on a slope at a time and avoid steep terrain.

Avalanche Problem 2: Persistent Slab
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We have been talking about our persistent weak layers all winter so far and why they are concerning.  This is the storm we have been waiting for to give those layers a real test.  We have been tracking these layers through the snowpack as well as how widely distributed they are throughout the terrain.  The short version of the story is that we have a relatively complex snowpack with multiple weak layers that are widely distributed.  We would need a crystal ball to accurately predict how these layers are going to react to the load of fresh and wind blown snow that is getting added right now.  What we can accurately say is that this is the biggest storm cycle of the winter  so far and the probability of natural and human triggered avalanches is going to be increasing as the snow piles up.  Give the snowpack some time to adjust right now and avoid traveling on or near slopes that are steep enough to produce avalanches.  

advisory discussion

Let us know what you are seeing out there.  It helps us paint a better picture of the current conditions across the West Central.  It's easy to do, takes about 5 minutes and prompts you for pertinent snow and avalanche info.  If you see an avalanche, note the direction the slope faces, relative elevation, depth of the crown and try to get a pic if possible.  Your observations can make a difference.    Submit avalanche observations       Submit snowpack observations

recent observations

Weather stations nearby are showing winds gusting into the teens right now with gusts into the mid twenties overnight.  Later today SSW winds will increase.  Lower elevation snow depths are already at 8 inches and increasing at about an inch per hour.  Forecasts show that will also increase throughout the day.  Yesterday the new light density snow was already showing signs of instability with some cracking and sluffing occurring.  The clear, cold nights on Wednesday and Thursday added another thin layer of Surface Hoar into the equation. 

All signs are pointing towards a natural avalanche cycle during this multi-day storm cycle.  The timing is going to be tough to pin down but we have multiple avalanche problems that are waiting for a trigger.  Smaller storm slabs and building wind slabs are the most likely scenario and you are most likely to trigger these.  As these slabs grow, they are going to be breaking deep enough to bury a skier or snowmobiler.  Larger, more destructive slides are going to be possible as well, these are going to be deep, involve 2-4 feet of dense snow and could kill a person or break trees.  

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 16 deg. F.
Max. temperature in the last 24 hours: 16 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: NA mph
Maximum wind gust in the last 24 hours: NA mph
New snowfall in the last 24 hours: NA inches
Total snow depth: 39 inches
weather

...WINTER STORM WARNING REMAINS IN EFFECT UNTIL 5 PM MST
TUESDAY...

* WHAT...Heavy snow. In the west-central and Boise mountains
additional snow accumulations of 1 to 2 feet in mountain valleys
with up to 3 feet over the mountains. In the Upper Weiser River
basin additional accumulations of 9 to 18 inches. Gusty winds
will accompany snowfall at times.

* WHERE...Upper Weiser River, West Central Mountains and Boise
Mountains zones.

* WHEN...Until 5 PM MST Tuesday. There will be notable breaks in
the intensity of snowfall Saturday night and again on Monday.

* IMPACTS...Travel will be very difficult to impossible.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Snow. High near 30. South southeast wind 7 to 9 mph becoming southwest in the afternoon. Winds could gust as high as 23 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 2 to 4 inches possible. Snow. Low around 21. South wind 5 to 7 mph becoming light and variable. Winds could gust as high as 24 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 3 inches possible. Snow. High near 28. South southeast wind 6 to 11 mph, with gusts as high as 20 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 7 inches possible.
Temperatures: 30 deg. F. 21 deg. F. 28 deg. F.
Wind direction: SSE S SSE
Wind speed: 7-9, Gusts to23 5-7, Gusts to 24 6-11, Gusts to 20
Expected snowfall: 2-4 in. 1-3 in. 3-7 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Snow. High near 18. South southwest wind 11 to 16 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 6 to 10 inches possible. Snow. Low around 12. Wind chill values between -2 and 3. South southwest wind 10 to 13 mph, with gusts as high as 22 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 7 inches possible. Snow. High near 17. Wind chill values between zero and 5. South wind 11 to 16 mph, with gusts as high as 26 mph. Chance of precipitation is 100%. New snow accumulation of 9 to 13 inches possible.
Temperatures: 18 deg. F. 12 deg. F. 17 deg. F.
Wind direction: SSW SSW S
Wind speed: 11-16 10-13, Gusts to 22 11-16, Gusts to 26
Expected snowfall: 6-10 in. 3-7 in. 9-13 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.