THIS AVALANCHE ADVISORY EXPIRED ON March 5, 2018 @ 7:00 am
Avalanche Advisory published on March 4, 2018 @ 7:00 am
Issued by Jess Asmussen - Payette Avalanche Center
bottom line

Human triggered avalanches are possible at all elevations. Pockets of areas where human triggered avalanches are likely exist at upper elevations due to wind slabs that formed during and after the last storm cycle. These avalanches may occur on isolated terrain features where recent snow has loaded and they may be large enough to bury a person. Yesterday, a human triggered avalanche north of Brundage Ski Area demonstrated that the snowpack is still highly variable and sensitive to human triggers. 

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Character ?
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  • Likelihood ?
    Certain
    Very Likely
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  • Size ?
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Wind slabs that formed during the last storm are still lingering near ridges, in cross-loaded gullies, and in exposed areas. The most sensitive wind slabs exist on north to east facing terrain. Drifted snow, cornices above slopes, and shooting cracks can help to identify where these wind slabs exist. Significant cornice growth has occurred in many of these areas. Corniced ridges should be approached with caution as they often break off further from the edge than expected. 

 

advisory discussion

Conditions are variable across the forecast area right now. Our advisory is based upon a small number of observations. Please let us know what you are seeing out there whether it is deep stable snow or avalanche activity. Observations can be submitted here. The next avalanche advisory will be published March 9th. 

recent observations

A human-triggered avalanche just north of Brundage Ski Area yesterday (see picture below) demonstrated that there are still lingering instabilities and variability in the snowpack. This incident serves as a reminder that human triggered avalanches are still possible. Luckily, the skier was not caught in the avalanche. Near Tamarack and Brundage Ski Areas, multiple users were accessing the backcountry via the ski area in the last couple days. Although “side country” terrain is very close to ski area boundaries, these areas have not undergone avalanche control, and should be treated like other backcountry areas. Proper equipment, prudent terrain management, and one person at a time protocols are still very important.

During a tour yesterday in the Brundage backcountry, we were able to find evidence of wind loading at the upper elevations. Cornice size has increased significantly in the last week. Snow stability tests on a north aspect revealed a weak layer from the superbowl crust 40 cm from the surface. This layer failed in compression tests (CT22) but did not propogate during extended column tests (ECTN19).

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 8 deg. F.
Max. temperature in the last 24 hours: 18 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 3 mph
Maximum wind gust in the last 24 hours: 12 mph
New snowfall in the last 24 hours: Trace inches
Total snow depth: 65 inches
weather

.SHORT TERM...Today through Monday...Fog noted across a few areas
this morning, most notably across Baker County and into McCall.
Moisture from the departing trough will leave a few showers over
the central Idaho mountains today, with activity also possible
across the Southwest Highlands and into Twin Falls county. Models
continue to indicate a tightening pressure gradient across the
western Magic Valley this afternoon, but wind speeds associated
with this tightening have weakened in the most recent model runs.
Localized strong wind will be possible, but confidence is not
high enough in a widespread development to issue a highlight at
this time. A drier northwest flow anticipated for Monday across
the area, with slightly warming temperatures. Even with this
warming, however, temperatures remain between 5-10 degrees below
normal.

.LONG TERM...Monday night through Saturday...An upper level ridge
will bring dry conditions through at least Wednesday. The next
upper level trough remains on track to bring precipitation to the
region beginning early Thursday morning. The main trough passage
happens on Friday which will be the best chance for precipitation.
Snow levels start out around 4000 ft MSL as precipitation begins
to fall Thursday and rise to near 6000 ft MSL by Friday afternoon.
Temperatures climb through the period to near normal by Thursday
afternoon. Another high amplitude upper level ridge returns for
the weekend bringing near normal temperatures and dry conditions.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: A 30 percent chance of snow showers, mainly before 11am. Patchy fog before 11am. Otherwise, mostly cloudy, with a high near 30. Light and variable wind becoming northwest 5 to 8 mph in the afternoon. Total daytime snow accumulation of less than a half inch possible. A 30 percent chance of snow showers, mainly after 11pm. Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 15. West northwest wind around 6 mph becoming calm in the evening. New snow accumulation of less than a half inch possible. A 20 percent chance of snow showers. Patchy fog before 11am. Otherwise, mostly cloudy, with a high near 30. Calm wind becoming southwest around 6 mph in the afternoon.
Temperatures: 30 deg. F. 15 deg. F. 30 deg. F.
Wind direction: Northwest West northwest Southwest
Wind speed: 5-8 mph 6 mph 6 mph
Expected snowfall: Less than a half in. Less than a half in. in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: A 30 percent chance of snow. Mostly cloudy, with a high near 23. North northwest wind around 7 mph. Total daytime snow accumulation of around an inch possible. A 30 percent chance of snow. Mostly cloudy, with a low around 16. South southwest wind around 8 mph. New snow accumulation of less than a half inch possible. A 30 percent chance of snow, mainly before 11am. Partly sunny, with a high near 24. South southwest wind 6 to 9 mph. New snow accumulation of less than a half inch possible.
Temperatures: 23 deg. F. 16 deg. F. 24 deg. F.
Wind direction: North northwest South southwest South southwest
Wind speed: 7 mph 8 mph 6 to 9 mph
Expected snowfall: 1 in. less than a half in. less than a half 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.