THIS AVALANCHE ADVISORY EXPIRED ON January 21, 2018 @ 6:41 am
Avalanche Advisory published on January 20, 2018 @ 6:41 am
Issued by George Halcom - Payette Avalanche Center
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The avalanche hazard is Moderate above 6000 feet today.  Up to 18 inches of light new snow has potential to sluff. The combination of gusty winds from multiple points on the compass and over a foot of new snow have created new wind slabs on exposed terrain.  Below 6,000 feet the avalanche hazard is LOW.

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Dry
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Yesterday we observed about 18 inches of new snow that had a tenancy to want sluff, or to run with you on steep slopes. Many steep slopes have already slufffed naturally. Use caution, and good sluff management while riding or skiing in exposed terrain where you may get knocked off course, and into the many obstacles that have yet to be buried like rocks and trees. 

Avalanche Problem 2: Wind Slab
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This great storm that started on Thursday brought with it gusty winds that started from the Southeast and wrapped around the compass to the West during the day.  Wind speeds at Granite Mt were recorded near 30 mph.  The combination of a significant snowfall and wind will have created wind slabs on exposed upper elevation terrain.  These slabs are  going to likely be just below the ridgelines, but may form well down into the midslope....Pay attention to changes in the texture or look of the snow pack in areas that saw the direct effects of the winds and expect newly formed wind slabs on a variety of slopes today.   Cracking, or sudden changes in how deep you are traveling in the snow pack are indicators of wind slabs.   

We observed natural wind slab avalanches on E,NE slopes yesterday in the Grassy twins and Hazard Lakes area, and also got a report in the Titus lot from a local sledder of a natural wind slab that had pulled out during the storm about 18 inches deep. Time will likely heal the wind slab problem, but stay alert in wind loaded terrain.

recent observations

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Yesterdays storm laid down around 18 inches of snow that is resting on a thin crust that formed from the warmup. The upper 9 inches of new snow right now is very light density, the kind that snow lovers smile about, while checking for sluffs. Our test results on the crust were moderate in compression, but lacked energy to propigate. The rest of the snowpack seemed damp still, but on the path of freezing.

We observed natural wind slab avalanches on E,NE slopes yesterday in the Grassy twins and Hazard Lakes area, and also got a report in the Titus lot from a local sledder of a natural wind slab that had pulled out during the storm about 18 inches deep. Time will likely heal the wind slab problem, but stay alert in wind loaded terrain.

 

weather

Area Forecast Discussion National Weather Service Boise ID 309 AM MST Sat Jan 20 2018 .SHORT TERM...Today through Sunday...Upper trough over the area will gradually shift eastward today. Meanwhile, a disturbance in Washington and northern Oregon will move into the Idaho panhandle late this afternoon. Isolated snow showers are expected over the higher terrain, except scattered snow showers across the far north associated with the disturbance. An upper ridge will move in tonight through Sunday morning for dry conditions. Patchy valley fog could develop during that time due to mostly clear skies and light winds that accompany the ridge. The next Pacific system will move onshore Sunday morning and spread snow into southeast Oregon Sunday afternoon. Accumulations will be light, with up to an inch in the valleys and 1 to 2 inches in the mountains. Temperatures will be a few degrees above normal. .LONG TERM...Sunday night through Saturday...Active pattern will continue into next weekend. The next system will move across the forecast area Sunday night into early Monday bringing snow to most locations. Mountains will see decent snowfall of up to 6 inches by Monday morning. The valleys will see little snow accumulations as surface temperatures remain above freezing through the entire event. A brief break in precipitation for late Monday night and early Tuesday, with increasing westerly flow aloft over the area ahead of the next system. Southeasterly surface winds will allow temperatures to warm into the upper 40s/low 50s in the valleys Wednesday. Snow levels between 4000 to 5000 feet will make for mountain snow and valley rain Wednesday into Thursday. The trough and cold front move through late on Thursday, lowering snow levels back down to all areas. Most of the precipitation will be done by the time the cold air moves in Thursday night. Some snow showers in northwest flow will linger through Friday as the upper level ridge rebuilds over the region. Another Pacific system moves into the Pacific Northwest on Saturday. Models are in good agreement with keep much of this system north of the forecast area bring precipitation to our northern zones. Temperatures look to be above normal on Tuesday/Wednesday and back down near normal for Thursday/Friday warming back above normal on Saturday.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Isolated snow showers. Patchy fog before 11am. Otherwise, mostly cloudy, with a high near 29. Light and variable wind. Chance of precipitation is 20%. Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 14. Light and variable wind. A 20 percent chance of snow after 11am. Patchy fog before 11am. Otherwise, increasing clouds, with a high near 30. Calm wind becoming south southeast 5 to 9 mph in the afternoon.
Temperatures: 29 deg. F. 14 deg. F. 30 deg. F.
Wind direction: Variable Variable SSE
Wind speed: Light Light 5-9 in the afternoon
Expected snowfall: 0 in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Scattered snow showers, mainly after 11am. Mostly cloudy, with a high near 18. Northwest wind 3 to 5 mph. Chance of precipitation is 30%. Total daytime snow accumulation of less than a half inch possible. A 20 percent chance of snow showers. Mostly cloudy, with a low around 13. North wind around 6 mph becoming south southwest after midnight. A 20 percent chance of snow after 11am. Increasing clouds, with a high near 19. South wind 8 to 17 mph.
Temperatures: 18 deg. F. 13 deg. F. 19 deg. F.
Wind direction: NW N S
Wind speed: 3-5 6 8-17
Expected snowfall: Less than one half in. 0 in. 0 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.