THIS AVALANCHE ADVISORY EXPIRED ON December 22, 2015 @ 6:45 am
Avalanche Advisory published on December 21, 2015 @ 6:45 am
Issued by -
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With yet another large Pacific storm and yet another WINTER STORM WARNING headed into the advisory area today, the avalanche danger is CONSIDERABLE for all slopes above 6,000 feet and over 30 degrees. Winds will be out of the south-southwest today and will cause winds slabs to further develop on all leeward slopes. The Payette Avalanche Advisory Area has had measurable precipitation everyday for the last 11 days, these could prove to be dangerous times in avalanche terrain.

 

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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If the high winds that are being forecasted come to fruition, wind slabs are going to be developing at a rapid pace on leeward slopes in elevations over 7,000 feet. These are easy to avoid if you watch the wind transport through the day and recognize where these tender wind slabs will be lurking. Remember as Bob Dylan once said..."you don't need a weather man to tell which way the wind blows" Please use caution and avoid these wind loaded slopes.

Avalanche Problem 2: Storm Slab
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10-24 inches of snow are forecast to fall in the West Central Mountains in the next 24 hours. That much snow that quickly has a hard time becoming cohesive with the existing snowpack which makes for tender soft slabs on all aspects. While not as deadly as hard slabs, these soft slabs definitely deserve respect. Stay away from slopes over 30 degrees where these soft slabs will be likely. Today is not the day for checking off big lines, keep to conservative terrain and enjoy the powder!

Avalanche Problem 3: Loose Dry
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As Dave B. mentioned in his advisory yesterday, loose dry avalanches or sluffs are becoming more of a problem. We have a lot of unconsolidated snow on the ground and if you are in steep or confined terrain these small slides can push you off course and into or over obstacles you would rather avoid. Be aware of where your partners are and don't push a sluff down on to them. The issue of loose dry avalanches will continue to grow today on all steep terrain as we pick up another 10 inches of new snow through the day.

advisory discussion

With the strong winds and heavy snowfall of yet another WINTER STORM WARNING caution is advised in the backcountry of Idaho today. Remember the basics...beacon, probe, shovel. One person on a slope at a time. Be mindfull of 'red flags' (recent avalanches, wind loading, cracking or whoomping on the snowpack).

 

recent observations

While out in the advisory area yesterday, my touring partner and I were unable to get any of the recent storm layers to propagate in any of our Extended Column Tests. This does not mean that these slabs aren't going to cause any problems today or in the future. Currently these slabs ARE reactive (initiation) at the interface between the different layers from the past storms (CT 13 40cm from surface Q2), but lack the cohesion that they need to propagate (ECTX). The rain crust from mid-November is still holding strong at 5 cm thick and is buried approx. 110 cm down in the pack at 7500 feet.

Check out the OBSERVATION page on the PAC website for more information.

 

weather

With an "impressive" plume of moisture being directed towards the Pacific Northwest and Northern California, yet another WINTER STORM WARNING is in effect until 8 AM Tuesday morning. Precipitation associated with this STORM WARNING will be widespread across southwest Idaho this morning and through the afternoon. Expect to see snowfall in the advisory area start mid morning with up to 1 inch of SWE (snow water equivalent) by this evening. Strong winds with speeds sustaining around 15-30 MPH and gusts up to 55 MPH in high elevations are on tap for today. This wind combined with up to 10-20 inches of new snow will make for hazardous avalanche conditions through this evening and into tomorrow. 

 

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Monday Monday Night Tuesday
Weather: Snow. High near 30. Light south southeast wind becoming south 8 to 13 mph in the morning. Chance of precipitation is 100%. Total daytime snow accumulation of 3 to 5 inches possible. Snow. Low around 22. Southwest wind 9 to 17 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 2 inches possible. A 50 percent chance of snow. Cloudy, with a high near 25. Southwest wind around 6 mph. New snow accumulation of less than a half inch possible.
Temperatures: High 30 deg. F. Low 22 deg. F. High 25 deg. F.
Wind direction: South-southeast Southwest Southwest
Wind speed: 8-13 9-17 6
Expected snowfall: 3-5 in. 1-2 in. .5 in.
Granite Mountain at 7700 feet.
  Monday Monday Night Tuesday
Weather: Snow. Areas of blowing snow. High near 22. Wind chill values between zero and 5. Windy, with a south southwest wind 20 to 30 mph increasing to 33 to 43 mph in the afternoon. Winds could gust as high as 55 mph. Chance of precipitation is 100%. New snow accumulation of 7 to 11 inches possible. Snow. Areas of blowing snow. Low around 16. Wind chill values between -2 and 3. Windy, with a west southwest wind 36 to 41 mph decreasing to 28 to 33 mph after midnight. Winds could gust as high as 55 mph. Chance of precipitation is 90%. New snow accumulation of 3 to 5 inches possible. Snow likely, mainly before 11am. Cloudy, with a high near 17. Wind chill values between -3 and 2. Breezy, with a west northwest wind 13 to 23 mph. Chance of precipitation is 70%. New snow accumulation of 1 to 3 inches possible.
Temperatures: High 22 deg. F. Low 16 deg. F. High 17 deg. F.
Wind direction: South-southwest West-southwest West-northwest
Wind speed: 20-30 gusts as high as 55 36-41 decreasing to 28-33 after midnight 13-23
Expected snowfall: 7-11 in. 3-5 in. 1-3 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.