Avalanche Advisory published on March 9, 2018 @ 6:41 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

Moderate Avalanche Hazard exists throughout the West Central Mountains, human triggered avalanches are possible today.  New wind slabs have formed in the last 24 hours and will continue to build through the day today.  Older wind slabs from last week's storms are still possible and may be overlying a weak layer of facets above the early February rain crust.  Watch for visual clues of where these new slabs are forming and where old wind slabs still exist.

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 ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Last week's storm left us with wind slabs on a variety of aspects, some of these slabs are resting on a weak layer of snow above the Superbowl weekend crust.  This layer has produced human triggered avalanches in the last week.  While these slabs are not widespread, their ability to propagate and the unpredictable nature of their distribution should cause you to approach steep, exposed terrain with caution today and through the next few days.  Moderate SW winds and a few inches of new snow will be creating a fresh crop of windslabs today. Watch for visual clues of wind effect and manage your slope angles as you travel in wind affected terrain.

Avalanche Problem 2: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

A layer of faceted snow exists above the February 4th crust and has produced avalanches in windloaded areas over the last 2 weeks.  This layer is now buried just about 2-3 feet down in the snowpack and has shown the potential to propagate easily when triggered by a skier or rider which is what happened on the W/SW aspect of Sargent's Mt. that produced a good sized avalanche last Sunday.  In some areas, this layer bonded to the new snow above and the crust has broken down or was very weak to begin with, in other areas. possibly more prevalent in the middle elevations 6500-7500 feet,  the crust and facet combo persists and should be taken very seriously.  The only 2 ways you are going to insure your safety are by either digging in and finding out if this layer is present where you are riding or skiing or by avoiding slopes over 35 degrees.  You can also help minimize your risk by using good travel protocols and avoiding steep, rocky areas where the snowpack is less uniform and you are more likely to find a shallow trigger point.

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. 

recent observations

Check out the recent observations we recieved from the avalanche on Sargents Mt.  right outside the Brundage Ski Area Boundary.  There were 2 different avalanches that wer triggered in this easy to access area.  The larger of the 2 was not reported by the party that triggered it.  Please take the time to post your observation and avalanche pictures to the PAC, it is easy, it's quick and may help someone else stay out of trouble.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 24 deg. F.
Max. temperature in the last 24 hours: 26 deg. F.
Average wind direction during the last 24 hours: W/SW
Average wind speed during the last 24 hours: 9 mph
Maximum wind gust in the last 24 hours: 27 mph
New snowfall in the last 24 hours: inches
Total snow depth: 59 inches

.DISCUSSION...Weakening Pacific upper trough will move due east
across nrn WA today and into MT tonight. Poorly-defined surface
cold front in OR this morning will move into wrn ID midday and
eastern ID tonight. Pacific moisture will also come inland across
nrn Calif, srn OR, and srn ID today. Showers will increase in our
zones today as the moisture gets drawn into the cold front. After
the front passes, the moist band will shift south to our srn CWA
border and our nrn zones will begin to clear. Patchy fog will
develop in nrn valleys overnight and early Saturday morning.
Tonight will be a little colder than the current night. Saturday`s
highs will be like today`s highs. Winds will be light south or
southeast this morning, light to moderate west/northwest behind
the cold front this afternoon, light and variable tonight, then
light to moderate easterly Saturday.

.LONG TERM...Saturday night through Friday...A transitory upper
level ridge will continue its progression east on Sunday, though it
will be briefly suppressed Sunday morning. Temperatures will warm to
about 10 degrees above normal Monday as a deep upper level trough
digs south off the Pacific coastline and a southwesterly flow aloft
prevails. Showers will begin as early as Tuesday afternoon from west
to east as the upper low moves into the Intermountain West. The best
chance of precipitation comes as the initial cold front moves across
the region Tuesday afternoon and evening, with temperatures dropping
to near normal Wednesday. Thunderstorms are possible with the cold
frontal passage, generally focused across southwest Idaho, but has
been left out of the forecast for now as confidence in frontal
timing remains low. Conditions remain unsettled through the end of
the period as the deep upper low progresses inland. Snow levels will
be high across the region as showers spread eastward with
precipitation beginning as rain in most locations, except for along
the highest peaks. As the upper low moves overhead Friday,
temperatures will fall to about 5 degrees below normal.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: Rain and snow showers. High near 39. South southwest wind 7 to 11 mph. Chance of precipitation is 80%. Total daytime snow accumulation of less than a half inch possible. A slight chance of rain and snow showers before 11pm. Patchy fog after 11pm. Otherwise, partly cloudy, with a low around 13. Southwest wind 5 to 10 mph becoming light and variable in the evening. Chance of precipitation is 20%. Patchy fog before 8am. Otherwise, sunny, with a high near 41. Light and variable wind.
Temperatures: 39 deg. F. 13 deg. F. 41 deg. F.
Wind direction: S/SW SW Variable
Wind speed: 7-11 5-10 Light
Expected snowfall: 1/2 in. in. 0 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Snow showers. High near 25. Southwest wind 15 to 17 mph. Chance of precipitation is 80%. Total daytime snow accumulation of 2 to 4 inches possible. A 20 percent chance of snow showers before 11pm. Partly cloudy, with a low around 16. West southwest wind 9 to 14 mph becoming light and variable after midnight. Sunny, with a high near 28. Calm wind becoming south around 6 mph in the afternoon.
Temperatures: 25 deg. F. 16 deg. F. 28 deg. F.
Wind direction: SW W/SW S
Wind speed: 15-17 9-14 6
Expected snowfall: 2-4 in. in. in.

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.