THIS AVALANCHE ADVISORY EXPIRED ON January 18, 2016 @ 7:02 am
Avalanche Advisory published on January 17, 2016 @ 7:02 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Danger is Considerable today on wind loaded, upper elevation slopes. Buried weak layers on protected aspects will make it possible to trigger avalanches in non wind affected terrain. Expect the avalanche danger to rise later in the day and tonight as temperatures and snow levels rise.  Increasing wind speeds today and an additional 10+ inches of snow tonight will add to our current avalanche problems. Conservative route selection and good travel protocols are essential survival tools right now.

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Wind slabs and wind loaded terrain remain the primary concern today.  They are widespread in the upper elevations and range in sensitivity from easily triggerable to resistant. They also range in size from a few inches to a few feet in some areas. New snow over the last few days has also done a great job camouflaging some of the wind slabs formed earlier this week, so the tell tale signs may be covered. Additional winds yesterday have added to the problem and winds will increase again today.  With plenty of light snow available for transport, Northerly terrain is suspect right now.  You may also find crossloaded areas on SE, E and W facing aspects where smaller terrain features have caught the blowing snow. Remember that wind slabs will often allow you to get further out on them than a storm slab before they fail.  Also, some of these wind slabs may be resting on a weak layer of faceted snow or surface hoar that was buried earlier in the week.  Your best bet is to avoid steep, wind loaded areas right now and through the next few days.

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

 Several different weak layers formed on or near the snow surface during the last period of high pressure and are lurking in our snowpack right now.  These persistent weak layers have slowly been buried this week and have failed(natural avalanche cycle mid week) in some areas and are still waiting for a trigger in other places.  These layers include buried surface hoar and near surface faceted snow on shadier aspects and a series of unsupportable and supportable crusts on the Southerly aspects. If you take 5 minutes to dig into the snow right now, you can see exactly where these layers are, they are pretty obvious in the snowpack. Surface Hoar and faceted snow are responsible for the majority of avalanche incidents and fatalities throughout the world. As we get additional snowfall combined with warming temperatures and strong winds, there is a good possibility that we will see another round of natural avalanches.  The risk of human caused avalanches will be rising today and tomorrow as well. The avalanche problem is increasing in both probability and size right now and requires an attitude and mindset adjustment from what we have been seeing over the last few weeks. Gone is the time for a go for it attitude, now is the time to travel safe and avoid steep terrain.

recent observations

Local ski resorts are showing 10 inches of new snow in the last 48 hours. Cooling and drying conditions Thursday and Friday nights left us with a soft and mostly unconsolidated layer of new snow above the older snow layers.  This is probably why we did not get more reports of skier or sled triggered avalanches yesterday and Friday. We have seen plenty of natural activity over the last few days on Northerly and Southerly aspects though so don't be lulled into complacency by what is not happening.  The layer of buried surface hoar and the collapsing crusts on the Southern exposures have the potential to get overloaded in the next 48 hours with rising temps, heavy precipitation and additional wind loading. Play it safe, avoid steeper terrain, watch your partners and make sure everyone in your group is carrying and knows how to use their rescue gear.

weather

Rising temperatures are going to be the main story today.  Expect to see a rising snowline through the day today possibly as high as 6500 feet. Winds will pick up through the day with more snow beginning late morning to early afternoon. This next storm is quite a bit wetter than our last storm and will be accompanied by strong South and Southwest winds with gusts into the mid 30's. NWS Boise office is predicting 1-3 inches today with an additional 4-8 inches over night.  Other computer models are forecasting over 10 inches for the West Central and Central Idaho mountains.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: Snow after 11am. Patchy fog before 11am. High near 31. Calm wind becoming south southeast around 5 mph in the afternoon. Chance of precipitation is 90%. Rain and snow. Low around 31. South southeast wind 5 to 7 mph. Chance of precipitation is 90%. Rain and snow showers likely, mainly before 11am. Cloudy, with a temperature rising to near 35 by 8am, then falling to around 26 during the remainder of the day. South wind around 5 mph becoming calm in the morning. Chance of precipitation is 60%.
Temperatures: 31 deg. F. 31 deg. F. 35 deg. F.
Wind direction: S S/SE S
Wind speed: 5 5-7 5
Expected snowfall: 1-2 in. 3-5 in. 1 in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: Snow after 11am. High near 32. South southwest wind 8 to 18 mph. Chance of precipitation is 90% Snow. Low around 28. Breezy, with a south southwest wind 20 to 24 mph, with gusts as high as 33 mph. Chance of precipitation is 100% Snow showers likely, mainly before 11am. Mostly cloudy, with a temperature falling to around 22 by 3pm. West wind 11 to 16 mph decreasing to 5 to 10 mph in the morning. Chance of precipitation is 70%
Temperatures: 32 deg. F. 28 deg. F. 32 deg. F.
Wind direction: S/SW S/SW W
Wind speed: 8-18 20-24 with gusts to 33 11-16
Expected snowfall: 1-3 in. 4-8 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.