THIS AVALANCHE ADVISORY EXPIRED ON January 28, 2016 @ 6:10 am
Avalanche Advisory published on January 27, 2016 @ 6:10 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The avalanche danger is Moderate on wind-loaded upper and mid elevation terrain. Moderate danger means it is possible for skiers or riders to trigger avalanches in steeper terrain. Sluffing and shallow wind slabs should be anticipated in steeper wind loaded terrain today. It is still possible to trigger a deeper layer of buried surface hoar that exists in some northerly terrain. At middle and low elevations, small wet slides and increasing rollerball activity should be expected as temperatures rise.

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
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Wind slabs continue to be a problem in the upper or wind exposed middle elevations. You are most likely to find these slabs at or near the ridgetops or in exposed terrain above 7,000 feet. They are still relatively widespread in the upper elevations and range in sensitivity from easily triggerable to resistant. Shallow wind slabs are more likely right now but you may also find some deeper ones still lingering under a layer of new snow. New snow over the last few days has also done a great job camouflaging some of the wind slabs formed last week, so you may not see any visual clues until it is too late. These slabs range in density between soft to hard, which means they may let you get well out onto them before they fail. Also, some of these wind slabs may be resting on a layer of faceted snow or surface hoar that was buried last week which may allow them to release deeper still. Your best bet until our snowpack begins to 'heal' is to take the time to assess the snowpack on each slope before you commit.

Avalanche Problem 2: Persistent Slab
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A weak layer, Surface Hoar, was buried 2 weeks ago and began producing natural and human triggered avalanche activity in sheltered terrain in the northern half of the PAC advisory area. This layer has been slowly covered, and has failed in some areas, and is still waiting for a trigger in other places. Buried surface hoar and faceted snow have the ability to propagate over large areas when they fail and are responsible for most avalanche incidents and fatalities. Over the last 2 days, a fresh crop of Surface Hoar has grown on the snow surface making skiing even better, unfortunately, this may become our next weak layer. As the snow begins to accumulate over the next 2 days, you will want to take a look at the snow and see what's going on with this layer.

Avalanche Problem 3: Loose Dry
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We saw some fairly decent natural Loose Dry avalanche activity yesterday in a steep, north facing bowl yesterday in the Trail Creek drainage. The largest was in a confined gulley, possibly resulting from a cornice failure. If you are skiing in steeper terrain today, you will need to anticipate sluff activity and have a plan so you don't get knocked down or off course. In confined terrain, sluffs can pile up and gain momentum pretty quick.

recent observations

We observed some decent sluffing or loose dry avalanche activity on a steep Northerly slope yesterday in the Trail Creek drainage. We were unable to locate the layer of buried surface hoar in our NNE pit at 7900 feet that we have been discussing over the last week. We did find some shallow instabilities in the upper portion of the snowpack that failed in Compression Tests at density changes between the new and older, firmer snow below. CT scores were 12 and 18 at the 25 and 35cm layers.

weather

TODAY THROUGH THURSDAY...UPPER LEVEL TROUGH REMAINS
OVERHEAD TODAY AS A SHORTWAVE MOVES UP AND OVER THE FLOW. NOT
MUCH MORE THAN CLOUD COVER FOR THE NW THIRD OF THE CWA IS
EXPECTED FOR TODAY. NEXT PATTERN CHANGE ARRIVES THURSDAY
AFTERNOON AS AN ATMOSPHERIC RIVER EVENT SETS UP. TEMPERATURES
EXPECTED TO BE ABOVE NORMAL AND SNOW LEVELS WILL BE ON THE
INCREASE AS PRECIP MOVES IN NW TO SE WITH THE FIRST SHORTWAVE.

.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...UPPER TROUGH CROSSES
THE REGION BY EARLY FRIDAY WITH MOIST SW FLOW TO FOLLOW. BY FRIDAY
AFTERNOON DEEPER MOISTURE PLUME WILL INTERACT WITH A TRAILING UPPER
SHORT WAVE TROUGH TO BRING MORE RAIN/SNOW TO SE OREGON AND SW IDAHO
FRIDAY INTO FRIDAY NIGHT. SNOW LEVELS ARE GENERALLY 4-5K FEET ACROSS
E-CENTRAL OREGON AND THE WEST-CENTRAL ID MTNS. THEY RISE TO THE
SOUTH...REACHING 7K FEET ALONG THE ID/NV AND OR/NV BORDER. WITH A
SUB-TROPICAL SOURCE REGION EXPECT HEAVIER PRECIP AMOUNTS THROUGH
FRIDAY NIGHT AND WILL NEED TO WATCH FOR POTENTIAL SNOW HIGHLIGHTS
ACROSS NORTHERN ZONES. PRECIP TAPERS OFF AND SNOW LEVELS FALL AS THE
SHORT WAVE TROUGH SLIPS EAST OF THE AREA FRIDAY NIGHT. SATURDAY
THROUGH TUESDAY ARE COOL AND UNSETTLED AS THE INTERIOR NW REMAINS
POSITIONED UNDER A BROAD UPPER TROUGH. TEMPERATURES WILL BE AT OR
SLIGHTLY BELOW NORMAL WITH SHOWER ACTIVITY FOCUSING IN THE MTNS.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Wednesday Wednesday Night Thursday
Weather: Mostly cloudy, with a high near 33. Calm wind. Mostly cloudy, with a low around 25. Calm wind. Rain after 11am. High near 35. Light and variable wind. Chance of precipitation is 80%.
Temperatures: 33 deg. F. 25 deg. F. 35 deg. F.
Wind direction: Calm Calm Variable-S/SW
Wind speed: Calm Calm Light
Expected snowfall: 0 in. 0 in. Trace in.
Granite Mountain at 7700 feet.
  Wednesday Wednesday Night Thursday
Weather: A 20 percent chance of snow before 11am. Mostly cloudy, with a high near 36. South southwest wind 6 to 10 mph. Mostly cloudy, with a low around 29. Southwest wind 10 to 13 mph. Snow, mainly after 11am. High near 36. Breezy, with a south southwest wind 13 to 21 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 3 inches possible.
Temperatures: 36 deg. F. 29 deg. F. 36 deg. F.
Wind direction: S/SW SW S/SW
Wind speed: 6-10 10-13 13-21
Expected snowfall: in. in. 1-3 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.