THIS AVALANCHE ADVISORY EXPIRED ON January 6, 2018 @ 7:16 am
Avalanche Advisory published on January 5, 2018 @ 7:16 am
Issued by Jess Asmussen - Payette Avalanche Center
bottom line

Moderate avalanche danger exists today at mid and upper elevations due to persistent slabs that exist above the buried Thanksgiving rain crust. A secondary problem, wind slabs, can be found near ridges and other exposed areas. While these slabs may be difficult to trigger, the shallow snowpack and numerous obstacles will increase the consequences if you are caught in an avalanche. The safest terrain (and arguably best snow quality) can be found in low angled, sheltered areas. 

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

A persistent weak layer (45-60 cm from the surface) can be found just above the hard Thanksgiving rain crust. This layer doesn’t exist everywhere, but can be found in most mid to upper elevation areas. Failures in this layer may be difficult to initiate, but human triggered avalanches are possible. This layer is fairly continuous throughout many areas, and avalanches could be large enough to injure or bury a person.

Yesterday in the Fisher Creek Saddle area (8100 feet, NE aspect), snow stability tests were failing and propagating with clean, fast shear qualities – ECTP 23 and PST 40/100 (End) (see video). Observers in the Jughandle Mountain area and Lick Creek area have noted similar results with clean shears and propagation during their tests.

Avalanche Problem 2: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Wind slabs are present near ridges and in exposed areas all across the forecast area. The wind slabs are shallow (less than 20 cm) and have been reactive to ski cuts. They are unlikely to bury a person, but they may push you into obstacles, or worse, trigger the deeper persistent slab below. Common signs of wind slabs are drifted, textured, hollow snow. 

recent observations

Yesterday in the Fisher Creek Saddle area, north of Brundage Mountain, we found a mix of conditions. The persistent slab was found on most aspects and elevations. Gusty winds over the last week have created wind slabs at and near the ridgelines. Warm temperatures and sunny skies have begun to create sun crust on solar aspects. Overall, good skiing and riding conditions can still be found at the upper elevations. Lower elevations have a thin snowpack, with lots of rocks and stumps still present.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 28 deg. F.
Max. temperature in the last 24 hours: 36 deg. F.
Average wind direction during the last 24 hours: 169
Average wind speed during the last 24 hours: 4 mph
Maximum wind gust in the last 24 hours: 15 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 69 inches
weather

SHORT TERM...Today through Saturday...Southeast Oregon and the west-central Idaho mountains will see a chance for light showers today. Freezing rain is possible at lower elevations while in the mountains, snow levels will be around 6k feet. Amounts will be light, with liquid totals less then 0.05 inches and snow accumulations less than an inch. For tonight into Saturday, an upper trough will track through the Pacific NW, bringing widespread precipitation. Lower valleys/basins in northern Malheur, Harney and Baker counties and the Weiser basin and lower Treasure Valley (west of the Ada/Canyon county line) could see freezing rain, especially at the onset when precipitation intensity is light. Otherwise snow levels are 6-7k feet ahead of the cold front so remaining valley locations will see a cold rain. Most model guidance continues to show heavier precipitation development along front as it moves into far southeast Oregon (southern Malheur county) and southwest Idaho early Saturday morning (liquid amounts of 0.1 to 0.3 inches, including valleys). Drier conditions develop west to east on Saturday as the upper trough pushes into eastern Idaho. Scattered snow showers will continue in the mountains through the day as snow levels drop to around 5k feet.

LONG TERM...Saturday night through Thursday...The latest model runs are in good agreement this morning. An exiting trough early on Sunday will give way to dry conditions as a ridge tries to build in. However, by Monday afternoon, another trough off the coast is expected to move inland. Widespread precip is expected as the area is in the warm sector. Models indicate that this trough will send a piece of energy off to the south leaving the area in split/zonal flow by Tuesday. Showers are expected to continue through Thursday, before another fast moving trough moves through on Friday. Temperatures are expected to be near or just above normal through the period.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: A chance of snow before 11am, then a chance of rain and snow. Cloudy, with a high near 34. Calm wind. Chance of precipitation is 30%. Total daytime snow accumulation of less than a half inch possible. Rain likely before 11pm, then rain and snow. Low around 29. Light south wind. Chance of precipitation is 80%. New snow accumulation of less than a half inch possible. A chance of rain and snow. Mostly cloudy, with a temperature falling to around 25 by 11am. Light and variable wind. Chance of precipitation is 50%. New snow accumulation of less than a half inch possible.
Temperatures: 34 deg. F. 29 deg. F. 25 deg. F.
Wind direction:
Wind speed: Calm Calm Calm
Expected snowfall: less than 1 in. less than 1 in. less than 1 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: A 40 percent chance of snow. Cloudy, with a high near 35. South wind 15 to 18 mph, with gusts as high as 25 mph. Total daytime snow accumulation of less than a half inch possible Snow. Low around 26. South southwest wind 8 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 90%. New snow accumulation of 1 to 3 inches possible. Snow likely, mainly before 11am. Mostly cloudy, with a high near 31. South southwest wind 5 to 8 mph becoming calm in the afternoon. Chance of precipitation is 60%. New snow accumulation of around an inch possible.
Temperatures: 28-35 deg. F. 26 deg. F. 31 deg. F.
Wind direction: South southwest South southwest
Wind speed: 8-18 5-8
Expected snowfall: less than 1 in. 1-3 in. 1 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.