THIS AVALANCHE ADVISORY EXPIRED ON January 14, 2020 @ 6:59 am
Avalanche Advisory published on January 13, 2020 @ 6:59 am
Issued by George Halcom - Payette Avalanche Center
bottom line

High Avalanche Danger remains. Wind slab and storm slab avalanches are likely on all steep terrain today.  Strong South/Southwest winds upwards of 30 MPH and snow are continuing in upper elevations. 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.

 

How to read the advisory


  • Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

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 24 hours along with winds in the teens gusting almost to 30 mph. This is a perfect wind loading situation.

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
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

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

received_900023397062146.jpeg (4032×1960)bfbebabf-7efe-48c9-91e0-873398e7f555.jpeg (3024×4032)

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 7 deg. F.
Max. temperature in the last 24 hours: 16 deg. F.
Average wind direction during the last 24 hours: S
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: 41 inches
weather

 

Area Forecast Discussion
National Weather Service Boise ID
402 AM MST Mon Jan 13 2020

.SHORT TERM...Today through Wednesday...A broad upper trough will
remain over the Pacific NW through Wednesday. Northwest flow in
the wake of an exiting shortwave will keep light snow across the
e-central Oregon and w-central Idaho mountains today. Another
system drops into the Pacific NW Monday night, returning
widespread snow to the region. Mountains will again see the
heaviest snowfall from Monday night into Tuesday, with lighter
but notable amounts across lower elevations. The forecast start
time of the snowfall across the Snake Plain is slightly sooner,
with light snow developing in the evening. This faster timing may
cut down on accumulations, especially across warmer portions of
the lower Snake Plain. Windy conditions will continue across the
region through Tuesday evening. The upper wave exits the region
late Tuesday with snow continuing in the mountains, but decreasing
in coverage and intensity. Lower elevations dry out Tuesday night
into Wednesday while a chance of snow showers remains across the
mountains. Temperatures will be near normal through Tuesday,
dropping below normal on Wednesday.

.LONG TERM...Wednesday night through Sunday...An upper level
trough off the Washington-Oregon coast Wednesday night will move
inland and weaken on Thursday, bringing 2 to 5 inches of snow to
the central Idaho mountains, but only light amounts elsewhere.
Following this system, weak high pressure will end the snow at
lower elevations Thursday night, but scattered snow showers will
continue over the central Idaho mountains. The next upper level
trough will spread more snow into eastern Oregon Friday night,
mainly north of Burns and Ontario. Temperatures will be near
normal. The trough is expected to weaken as it crosses the
region on Saturday with a chance of light snow. Drier conditions
develop Sunday as an upper ridge builds over the Pacific NW.

&&

.AVIATION...This morning snow showers continuing over the west
central Idaho and Boise Mountains. Mainly VFR at lower elevations.
This afternoon widespread mountain obscuration in snow, with
IFR/LIFR conditions. Isolated to scattered snow showers in the
valleys. After 14/00z widespread snow all areas, decreasing to
scattered snow showers at lower elevations after 14/12z. Surface
winds southwest to west 10-20 kts. Winds aloft at 10k ft MSL
northwest 40-50 kts becoming west 40-50 kts after 18z.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Monday Monday Night Tuesday
Weather: Snow likely. Mostly cloudy, with a high near 24. South wind 7 to 10 mph, with gusts as high as 24 mph. Chance of precipitation is 70%. Total daytime snow accumulation of 1 to 2 inches possible. Snow. Low around 18. South southeast wind 7 to 9 mph, with gusts as high as 21 mph. Chance of precipitation is 90%. New snow accumulation of 2 to 4 inches possible. Snow. High near 24. South wind 7 to 9 mph, with gusts as high as 21 mph. Chance of precipitation is 90%. New snow accumulation of 2 to 4 inches possible.
Temperatures: 24 deg. F. 18 deg. F. 24 deg. F.
Wind direction: S SSE S
Wind speed: 7-10 mph Gusting 24 mph 7-9 mph Gusting 21 mph 7-9 mph Gusting 21 mph
Expected snowfall: 1-2 in. 2-4 in. 2-4 in.
Granite Mountain at 7700 feet.
  Monday Monday Night Tuesday
Weather: Snow. Steady temperature around 13. Wind chill values between -4 and 1. South southwest wind 10 to 14 mph, with gusts as high as 32 mph. Chance of precipitation is 80%. Total daytime snow accumulation of 2 to 4 inches possible. Snow. Low around 15. South wind 11 to 15 mph, with gusts as high as 28 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 southwest wind around 11 mph, with gusts as high as 24 mph. Chance of precipitation is 90%. New snow accumulation of 3 to 5 inches possible.
Temperatures: 13 deg. F. 15 deg. F. 17 deg. F.
Wind direction: SSW S SSW
Wind speed: 10-14 mph, Gusting 32 mph 11-15 mph, Gusting 28 mph 11 mph, Gusting 24 mph
Expected snowfall: 2-4 in. 3-7 in. 3-5 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.