THIS AVALANCHE ADVISORY EXPIRED ON February 16, 2019 @ 6:54 am
Avalanche Advisory published on February 15, 2019 @ 6:54 am
Issued by George Halcom - Payette Avalanche Center
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The Avalanche Hazard is High today. Natural Avalanches are likely and Human caused avalanches are very likely.  Strong winds and heavy snow have created dangerous wind slabs on upper elevation, exposed slopes that will continue today with a little more wind and snow.  Storm slabs are also likely on slopes over 30 degrees. Wait for the storm to calm down and allow the snow pack to adjust and re-freeze. Cooling temperatures today could make slabs initially brittle and reactive? 

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
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  • Size ?
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We have been seeing a lot of wind and snow for multiple storm cycles, and over the last few days this has created dangerous conditions on many upper elevation slopes.  Wind slabs have been growing, sliding, and re-forming daily. Natural wind slab avalanches have been observed over the last few days. Cooling today and into the extended forecast could make slabs brittle and reactive to the weight of a skier or rider? 

Some of these slabs are easy to feel or see but some are also getting covered up with the new and wind blown snow and will be difficult to recognize. Shooting cracks or hollow, sculpted snow are warning signs of wind slabs. Travel in wind loaded avalanche terrain is not recommended. Check out this short video of brittle wind slabs on a SW aspect from Tuesday.  Tamarack Ski Patrol also reported large avalanche activity that occurred both naturally and during avalanche mitigation operations Tuesday.  Cornice failures are a concern today as well. give cornices and slopes below them a wide berth.Wait for the storm to calm down and allow the snowpack to adjust and re-freeze. Cooling today and into the extended forecast could make slabs brittle and reactive? 

 

Avalanche Problem 2: Storm Slab
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  • Likelihood ?
    Certain
    Very Likely
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  • Size ?
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The amount of snow that has hit the West Central Mountains has been a big load really fast and pretty atypical for such a short time frame.  Temperature fluctuations and high winds have created slabs of various hardnesses across multiple slopes. Crusts, multiple graupple  layers and other weak layers exist within the snowpack and are buried 2-3 feet deep. Travel on steep slopes in the backcountry is not recommended at this time.  Wait for the storm to calm down and allow the snowpack to adjust and re-freeze. Cooling today and into the extended forecast could make slabs brittle and reactive? 

advisory discussion

PAC will issue 3 Advisories per week through the remainder of the winter as long as funding is available.

Please be aware that there are areas that are CLOSED to motorized traffic in the McCall, Goose Lake and greater West Mountains area.  Just because there are tracks in some areas, does not mean they are open.  Please respect all users and closures.  See the Payette Winter Travel Maps for clarification.  Both the East and West maps can be downloaded on the Avenza app on your phone or are available at trailheads and local shops.   IT IS YOUR RESPONSIBILITY TO KNOW WHERE YOU ARE AND WHERE THESE CLOSURES EXIST. 

recent observations

We had a fairly clear day Tuesday in between storms and were able to see Natural Avalanches on several upper elevation, wind loaded slopes.  In addition, slopes over 35 degrees were sluffing naturally and shedding some of the new snow.   Our 600's were challenged on all but the flattest terrain and we found challenging skiing conditions on Southerly, wind exposed slopes where stiff, wind slabs were cracking under the weight of our skis and failing on isolation in our pits(see video)  Deep snow is keeping sleds off steep slopes for now and avoiding the steeps for the next few days is the best thing you could do right now.  

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 20 deg. F.
Max. temperature in the last 24 hours: 28 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 8 mph
Maximum wind gust in the last 24 hours: 27 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: NA inches
weather

Area Forecast Discussion
National Weather Service Boise ID
311 AM MST Fri Feb 15 2019

.SHORT TERM...Today through Sunday...Upper trough off the coast
is now coming inland via WA and OR with lots of cold cu. A
surface cold front passed through our CWA late Thursday with
locally heavy showers and isolated thunderstorms. A secondary
cold front, currently in central Oregon, will pass through our
CWA this afternoon with more showers and isolated thunderstorms,
especially near the frontal zone. Meanwhile, significant new
snow will continue in the Boise Mountains and west central Idaho
Mountains as snow levels lower. We have issued a winter weather
advisory for those areas through the day. Gusty southwest winds
will blow this afternoon in southeast Oregon, but not quite
strong enough for a wind advisory. Colder weather with gradually
decreasing snow showers will continue in all areas through Saturday
and Sunday as the upper trough makes it way across the northern
Intermountain region.

.LONG TERM...Sunday night through Friday...A series of disturbances
will impact the region throughout the extended period. The first of
these will bring a chance of snow showers to our higher elevations
Monday. On Wednesday into Thursday another disturbance will drop
in from the north, this time bringing a bit more widespread
precipitation for the region. Some differences emerge with the track
of this low with the Canadian and ECMWF wanting to dig the low
much further south while the GFS is quick to push it east. These
differences will make the temperature forecast a bit tricky that
far out, but did trend our forecast toward the cooler solutions.

&&

.AVIATION...Mostly VFR. Snow showers will continue through the rest
of the morning bringing areas of MVFR/IFR conditions with mountain
obscurations. Snow showers will increase during the afternoon hours
impacting mostly higher elevations. Surface winds, southeast-
southwest 5-10kts except south of the Snake River Plain where
stronger winds of 15-20kts with gusts 25-30kts are expected. Winds
aloft to 10k feet MSL, southwest 30-40kts.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: Snow showers. Some thunder is also possible. High near 30. South southwest wind 6 to 8 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 3 inches possible. A 40 percent chance of snow showers. Mostly cloudy, with a low around 18. South southwest wind around 5 mph becoming calm in the evening. New snow accumulation of less than one inch possible. A 40 percent chance of snow showers. Mostly cloudy, with a high near 28. Light southwest wind. New snow accumulation of less than one inch possible.
Temperatures: 30 deg. F. 18 deg. F. 28 deg. F.
Wind direction: SW SSW SW
Wind speed: 6-8 5-Calm Light
Expected snowfall: 1-3 in. Less than one in. Less than one in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Snow showers. Some thunder is also possible. Temperature falling to around 14 by 5pm. South southwest wind around 9 mph. Chance of precipitation is 90%. Total daytime snow accumulation of 3 to 7 inches possible. A 50 percent chance of snow showers. Mostly cloudy, with a low around 9. South wind around 7 mph. New snow accumulation of 1 to 3 inches possible. A 50 percent chance of snow showers. Mostly cloudy, with a high near 16. South southwest wind 5 to 7 mph. New snow accumulation of 1 to 2 inches possible.
Temperatures: 14 deg. F. 9 deg. F. 16 deg. F.
Wind direction: SSW S SSW
Wind speed: 9 7 5-7
Expected snowfall: 3-7 in. 1-3 in. 1-2 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.