THIS AVALANCHE ADVISORY EXPIRED ON January 15, 2019 @ 6:07 am
Avalanche Advisory published on January 14, 2019 @ 6:07 am
Issued by George Halcom - Payette Avalanche Center
bottom line

The Avalanche Hazard is Moderate today.  Wind Slabs and Cornices remain a concern on exposed slopes and vary in their reactivity to skiers and snowmobiles.  Some of the wind slabs are resting on Graupel and weak layers persist deeper in the snow pack. Use caution in areas where wind slabs are present especially where the snow pack is still shallow.  Loose/Wet Avalanches will be a consideration on slopes affected by the Sun.

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 ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
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Wind Slabs are present in many upper elevation, wind exposed areas. Given the warm temperatures in the upper elevations from the inversion, these slabs should have stabilized for the most part by now, BUT in some areas these slabs are resting on a layer of Grauple and our Persistent Weak Layer of Basal Facets which could still faIl. 

You are most likely to trigger these wind slabs on high, northerly, leeward slopes but be aware of smaller terrain features  like gullies that have experienced cross loading especially on East and West aspects. You will want to pay attention to how your skis or sleds are traveling on the snow and how the snow feels in wind affected areas.  A quick mit pit, pole test or even stepping off your sled will give you an indication of what lies below the surface you are traveling on.

Last Thursday we toured into an area where we have been tracking both the effects of the wind in the upper elevations and the Persistent Weak Layers in more protected areas in the middle elevations.  The photos below show 2 VERY different snowpacks:

The middle elevation shows the trend that we expected to see with the warming temps this past week and an improving snowpack.  The Buried Surface Hoar  and Basal Facet Layers are rounding and gaining strength and the snowpack is getting deep enough  and strong enough to give us confidence in steeper terrain.

The upper elevation did not inspire the same confidence. We found a highly variable snowpack with thin rocky areas where the wind slabs were failing in isolation and in the moderate realm during our tests. More concerning was the lingering and reactive layer of Basal Facets that was well preserved at the bottom of the snowpack.  The  take home message is that while these areas are probably not the norm, you should still be wary of the upper elevation snowpack and avoid slopes steep enough to slide. avalanches triggered in the wind slabs have a small possibility of stepping down into the weak layer near the ground which would be very high consequence scenario.

Avalanche Problem 2: Loose Wet
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    Certain
    Very Likely
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  • Size ?
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The Sun will be out again today, and the inversion will persist through the day also. Expect to see continued Loose/Wet activity in the form of roller balls and point releases on steep slopes that are getting a good dose of the suns rays. 

 

 

advisory discussion

Due to the partial government shutdown, avalanche forecasting will be limited.  We expect to forecast 3 times a week until the shutdown has ended.

Your observations are very helpful to the PAC staff and help create a better picture of the complex terrain in our advisory area.  You can click on the add observations linkand add as little or as much detail as you have.  It is easy to navigate and will also upload pictures easily.  Please contribute to your local forecast by sharing what you see or experience even if it is just good snow. or a trip report.

recent observations

Inverted temperatures are heating up the snow, especially in combination with direct solar gain. Rollerballs and point releases have been reported. Conditions have been prime for surface hoar formation, and skiers are enjoying skiing through the feathers. Click here for observations that were submitted yesterday. 

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 37 deg. F.
Max. temperature in the last 24 hours: 44 deg. F.
Average wind direction during the last 24 hours: E
Average wind speed during the last 24 hours: 8 mph
Maximum wind gust in the last 24 hours: 20 mph
New snowfall in the last 24 hours: na inches
Total snow depth: na inches
weather

 

.SHORT TERM...Today through Wednesday...Fog noted across the lower
lying areas of the forecast area this morning, with additional fog
anticipated. High pressure and its inversion remain over the area.
Expect dry conditions with fog through Tuesday morning. An area of
low pressure off the California coast will swing a trough across
the area beginning Tuesday, which will kick off unsettled
conditions. Showers will first be present across the southern
quarter of the forecast area Tuesday afternoon, with activity
spreading north through the day, with the best coverage
anticipated over the mountains. The next, potentially stronger,
system will begin to spread showers into the area Wednesday
morning, with much of the area seeing showers by Wednesday
afternoon. Snow levels will rise during this second system,
bringing more rain or rain-snow mix conditions across valleys.
Mountain snow remains. Temperatures will be able to warm through
the period, with values reaching above normal by Wednesday.

.LONG TERM...Wednesday night through Sunday...Moist southwesterly
flow aloft will bring pcpn into our CWA Wednesday and Thursday.
Relative drying Friday as the main upper trough moves east of us.
Warm-front Saturday will bring clouds but little if any pcpn.
Upper ridge will Saturday night and Sunday morning with dry wx.
The next Pacific storm will split as it comes inland later Sunday
through Monday, bringing light amounts of pcpn Sunday and
Sunday night, clearing Monday.

&&

.AVIATION...Areas of MVFR/IFR in valley fog and low stratus
through 18Z. The main areas will be eastern Oregon, along the
Snake River in idaho, and the Upper Weiser Basin in Idaho.
Conditions will improve to generally VFR through 15/00Z then
fog and stratus will increase again. Elsewhere, VFR with clear
skies. Surface winds: variable 10kts or less. Winds aloft near
10k feet MSL: east-southeast 15-25 kts through 18Z then southeast
25-35 kts after 18Z.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Monday Monday Night Tuesday
Weather: Patchy fog. Otherwise, mostly sunny, with a high near 29. Calm wind. Patchy fog before 11pm. Otherwise, mostly clear, with a low around 11. Calm wind. Increasing clouds, with a high near 32. Calm wind.
Temperatures: 29 deg. F. 11 deg. F. 32 deg. F.
Wind direction: Calm Calm Calm
Wind speed: NA NA NA
Expected snowfall: 0 in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Monday Monday Night Tuesday
Weather: Sunny, with a temperature falling to around 28 by 5pm. South wind around 6 mph. Mostly clear, with a low around 16. South southeast wind around 7 mph. Mostly sunny, with a high near 26. South wind 5 to 7 mph.
Temperatures: 28 deg. F. 16 deg. F. 26 deg. F.
Wind direction: S SSE S
Wind speed: 6 7 5-7
Expected snowfall: 0 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.