THIS AVALANCHE ADVISORY EXPIRED ON January 13, 2020 @ 7:31 am
Avalanche Advisory published on January 12, 2020 @ 7:31 am
Issued by George Halcom - Payette Avalanche Center
bottom line

High Avalanche Danger remains in the upper elevations. Wind slab and storm slab avalanches are likely on all steep terrain today.  Most of the danger, and the most sensitive snow lies in the upper snow pack, but you could trigger an avalanche in older weak layers that are now buried 3-5 feet deep or more.  Expect High avalanche danger to rise through the day and continue through Monday.

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 and storm slabs are going to be your biggest concern today, tonight and tomorrow.  The forecast is calling for 1-2 feet in the upper elevations over the next 36 hours along with winds in the 20's gusting almost to 40 mph.

Light density snow is easily transported by the wind and can result in widespread wind loading.  You are MOST likely to find wind slabs near ridge lines and on cross loaded slopes(think gullies and sub-ridges) in the upper elevations but today wind slabs 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. 

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 snow pack as well as how widely distributed they are throughout the terrain.  The short version of the story is that we have a relatively complex snow pack 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 snow pack 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

We received widespread reports of new snow instabilities yesterday from Brundage Ski Patrol, Tamarack Ski Patrol, Backcountry Skiers and Snowmobilers who all were getting cracking and or triggering slides in the new snow yesterday. Check out our observations page, and some of the photos from backcountry skiers and snowmobilers below that submitted observations. Thanks for sharing!

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CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 12 deg. F.
Max. temperature in the last 24 hours: 18 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: 40 inches
weather

Area Forecast Discussion
National Weather Service Boise ID
258 AM MST Sun Jan 12 2020

.SHORT TERM...Today through Monday...Another north Pacific storm
will move into our CWA today with more heavy snow in northern
mountains. A winter storm warning will continue there all the
way through Tuesday, although latest models suggest it could last
until Wednesday morning. Have added the Owyhee Mountains to the
warning for today through late tonight. Removed the winter
weather advisory from eastern Oregon and southwestern Idaho for
today and tonight as too little snow is now forecast there, but
created a new advisory for the next storm expected Monday
afternoon through Monday night. As for today`s storm, models
are also showing enough instability for isolated thunderstorms
this afternoon and evening across our northern zones, including
Baker County, and Idaho from the Treasure Valley northward.
Any thunderstorms will enhance snowfall rates. Temperatures
today will be similar to yesterday but will trend a little colder
Monday. Southwest winds will be gusty today in southeastern
Oregon, and locally in Idaho near the Nevada border.
.LONG TERM...Monday night through Thursday...Strong westerly flow
aloft will continue the unsettled weather pattern. A Pacific
weather system will bring more snow Monday night into Tuesday
morning, with an inch or two possible at lower elevations and
5 to 10 inches in the west central Idaho and Boise Mountains.
Scattered snow showers will linger through Wednesday. The next
system will arrive on the coast Wednesday night and weaken as
it moves inland on Thursday. Only light snow amounts are expected
at lower elevations. Temperatures will average a few degrees
above normal Tuesday and Thursday and a few degrees below normal
on Wednesday.

Thursday night through Sunday...The upper trough will slide east
of the area Thursday night. Westerly flow behind the trough will
keep a chance of showers over the mountains on Friday while drier
conditions develop across the rest of the region. Another weak
system will move into the Pacific NW on Saturday though with
model differences in its track increasing uncertainty about
precipitation chances, especially across southern zones. The
forecast will trend drier on Sunday as an upper ridge builds
into the region. Temperatures will run near normal through the
period.

&&

.AVIATION...Mountains obscured in snow and low clouds, with
widespread IFR/LIFR conditions. Scattered MVFR/IFR snow showers
lower elevations. Snow becoming widespread this evening, ending
at lower elevations by 13/12z, but continuing over the higher
terrain. Surface winds south to southwest 5-15 kts, increasing
to 10-20 kts this afternoon. Winds aloft at 10k ft MSL west to
northwest 30-40 kts, increasing to 40-50 kts this afternoon.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Warning until 5 PM MST Tuesday IDZ011-013-033.
Winter Weather Advisory from 11 AM Monday to 5 AM MST Tuesday

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: Snow. Some thunder is also possible. High near 28. South wind 9 to 15 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 3 to 5 inches possible. Snow. Some thunder is also possible. Low around 16. South wind around 14 mph. Chance of precipitation is 100%. New snow accumulation of 2 to 4 inches possible. Snow. High near 22. South southwest wind 8 to 10 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 3 inches possible.
Temperatures: 28 deg. F. 16 deg. F. 22 deg. F.
Wind direction: S S SSW
Wind speed: 9-15 mph 14 mph 8-10 mph
Expected snowfall: 3-5 in. 2-4 in. 1-3 in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: Snow. Some thunder is also possible. High near 17. Wind chill values between -4 and 1. Breezy, with a south wind 18 to 23 mph increasing to 24 to 29 mph in the afternoon. Winds could gust as high as 38 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 10 to 14 inches possible. Snow. Some thunder is also possible. Low around 7. Wind chill values between -5 and -12. Breezy, with a south southwest wind 23 to 26 mph, with gusts as high as 36 mph. Chance of precipitation is 100%. New snow accumulation of 6 to 10 inches possible. Snow. High near 10. Wind chill values between -7 and -12. Breezy, with a southwest wind 16 to 20 mph. Chance of precipitation is 90%. New snow accumulation of 5 to 9 inches possible.
Temperatures: 17 deg. F. 7 deg. F. 10 deg. F.
Wind direction: S SSW SW
Wind speed: 18-29 mph, gusts 38 mph 23-26 mph, Gusts 36 mph 16-20 mph, Gusts 20 mph
Expected snowfall: 10-14 in. 6-10 in. 5-9 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.