THIS AVALANCHE ADVISORY EXPIRED ON January 7, 2018 @ 8:05 am
Avalanche Advisory published on January 6, 2018 @ 8:05 am
Issued by Dave Bingaman - Payette Avalanche Center
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BOTTOM LINE Moderate hazard exists today at mid and upper elevations due to a persistent weak layer above the Thanksgiving rain crust.  Isolated wind slabs can also be found near ridgetops and on upper elevation, exposed slopes. A rapid warmup yesterday and rain overnight to nearly 7000 feet will increase the avalanche hazard until temperatures allow the snowpack to refreeze.  Pay attention to changing conditions and a high level of variability as you travel through the mountains today.

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
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A persistent weak layer of faceted snow(2-3 ft from 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 above 7000 feet.  Over the last few weeks,  the snowpack above this layer has slowly consolidated into a significant slab.  Pit tests show the potential for propagation at this layer and while failure is relatively hard to initiate, human triggered avalanches are possible especially where the snowpack is thin or where the overlying slab is weaker.  Warming temperatures yesterday will increase the hazard until the snowpack has a change to solidly refreeze.  This layer is fairly continuous throughout the West right now and has already been responsible for several skier and snowmobiler burials in other parts of Idaho and nearby states.  Check out this short video to see what the layer is doing in our test pits around the McCall area.

Avalanche Problem 2: Wind Slab
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Isolated wind slabs are present near ridges and in exposed areas all across the forecast area right now. The wind slabs are shallow (around a foot) and have been reactive to ski cuts over the last week. We have also observed and had reports of natural avalanches on these isolated slabs over the last few days. 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 and hollow feeling or sounding snow. 

Avalanche Problem 3: Loose Wet
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Temperatures soared into the 40 degree range around 7000 feet yesterday, last night rain fell to nearly the same elevation with heavy, wet snow above.  The snowpack already has a variety of weak or bed surface layers which were just becoming a wet/loose problem yesterday afternoon.  We observed a rapidly warming snowpack that slid off of buried crusts easily and was beginning to produce roller ball activity.  Lower elevation slopes that were thin and lacked the crust were becoming unsupportable and punchy which presented a different kind of hazard while traveling slopes littered with buried obstacles.  The snowpack is going to take awhile to refreeze, upper elevation temps dipped into the 20's last night while the middle and lower elevation areas are still above freezing this morning.  Pay attention to the potential for wet loose avalanches on steep lower elevation terrain until we see a solid refreeze. 

advisory discussion

Your observations very important to help us generate a larger picture of snow and avalanche conditions, please let us know what you are seeing while you are out riding or skiing in the local backcountry.  It's super easy to send us info and photos with date, location, pictures, general or specific snow observations, just click on the submit observations page on the PAC website and add what you saw or found in the snow.  You can also email the forecasters directly at:  forecast@payetteavalanche.org

recent observations

We toured in the Duck Lake area of the upper 20 mile drainage yesterday.  The snowpack was highly variable and became extremely warm by mid afternoon.  We observed a  recent, small wind slab on the upper slopes of S. Rain Peak yesterday that was big enough to carry a skier or push a snowmobiler into the rocky slopes below.  In addition,  our test pits showed a wide range of variability with southerly slopes harboring a shallow, weak snowpack with several melt/freeze crusts present as well as a layer of well defined faceted snow near the ground. Northerly slopes had a solid, cohesive slab above the weaker layers below which made it difficult to trigger the faceted layer of snow above the well preserved Thanksgiving Crust.  Lower elevations were beginning to loose cohesiveness as temps climbed above 40.  The snowpack became sticky and unsupportable and was beginning to produce wet loose debris on steep rollovers especially where a melt freeze crust was present below.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 27 deg. F.
Max. temperature in the last 24 hours: 32 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 10 mph
Maximum wind gust in the last 24 hours: 20 mph
New snowfall in the last 24 hours: 1 inches
Total snow depth: 59.68 inches
weather

.SHORT TERM...Today through Sunday...Rain and snow will continue
this morning across much of the region as an upper wave tracks
along the ID/NV border. Precipitation will dissipate from west to
east ending in southeast Oregon by 18Z and across southwest Idaho
during the afternoon. Precipitation type will be rain or snow as
lower valleys/basins will remain above freezing today. Snow levels
of 6-7k feet MSL this morning gradually fall to around 5k feet by
afternoon. Any accumulations will be light and limited to sites
above 6k feet across the area. Precipitation lingers into the
evening over s-central ID, along the ID/NV border, otherwise
conditions are dry. Clearing skies and recent precipitation will
favor valley fog development Sunday morning. Sunday is dry but
with increasing clouds as an upper ridge rebuilds over the
Pacific NW. Temperatures are at or slightly above normal through
Sunday.

.LONG TERM...Sunday night through Friday...Existing ridge axis
will move east ahead of the next approaching trough on Monday.
Warm front with widespread precip will spread across the area late
Monday into Tuesday. Snow levels will be around 7000 ft along the
ID/NV border and taper off to around 5000 in the northern portions
of the CWA. Precip will continue through Tuesday, as a portion of
energy swings south. Despite the area being in somewhat of a
split flow, a cold front later on Tuesday will move through. A
ridge is expected to build once again off the coast Wednesday and
beyond. Models continue to show another fast moving trough coming
up and over the ridge impacting the area on Friday, but conditions
looks dry beyond then. Temperatures look to remain 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.
  Saturday Saturday Night Sunday
Weather: A chance of rain and snow, mainly before noon. Mostly cloudy, with a high near 36. Calm wind. Chance of precipitation is 40%. Little or no snow accumulation expected. Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 20. Calm wind. Patchy fog before 11am. Otherwise, mostly cloudy, with a high near 32. Light south southeast wind.
Temperatures: 36 deg. F. 20 deg. F. 32 deg. F.
Wind direction: Calm Calm SE
Wind speed: Calm Calm Light
Expected snowfall: 0 in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: A 40 percent chance of snow. Mostly cloudy, with a high near 31. Light northwest wind. Total daytime snow accumulation of less than a half inch possible. Mostly cloudy, with a low around 23. Calm wind becoming southwest 5 to 7 mph after midnight. Mostly cloudy, with a high near 29. Southwest wind around 10 mph
Temperatures: 31 deg. F. 23 deg. F. 29 deg. F.
Wind direction: NW SW SW
Wind speed: Light 5-7 10
Expected snowfall: Trace 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.