THIS AVALANCHE ADVISORY EXPIRED ON March 4, 2018 @ 7:07 am
Avalanche Advisory published on March 3, 2018 @ 7:07 am
Issued by Dave Bingaman - Payette Avalanche Center
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The Avalanche Hazard is Considerable on upper elevation, wind affected ridges and slopes.  Strong winds combined with recent snowfall have created sensitive wind slabs on both windward and leeward slopes affected by SE, SW and S winds over the last few days.  Avoid traveling on or near corniced ridgelines as newly formed cornices are very sensitive and breaking farther back than you might expect. Loose snow avalanches or sluffs are likely on terrain over 35 degrees.

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Winds have been gusting for the last 2 days and have had plenty of light density snow to pick up and move around.  Ridgetop winds peaked last Thursday night with gusts approaching 50 mph adding even more snow to our wind slab problem.  Sensitive wind slabs are most likely to be found on East and Northerly terrain and range in size from a few inches to over a foot thick.   You may also find cross loaded areas of wind slab on windward terrain features on other aspects. The higher the terrain or the more exposed the terrain is, the more likely you are to encounter these slabs and the larger they are likely to be.  Some of these slabs may be resting on older, firm wind slabs below or on a layer of weaker snow that formed earlier this week. 

Large cornices are now hanging on most of the upper elevation ridgelines and should be avoided.  These new cornices are very soft and may break 4 or more feet back from the lip or edge when approached.

For the most part the wind slab problem is easy to recognize, wind affected snow will give you plenty of visual clues today with spines, drifts, pillows, and rippled wind rows visible on most wind exposed terrain today.  In addition, if you are riding or skiing and notice a sudden change in the surface of the snow from soft to more firm or hard, you are on a wind slab.  Thick, hollow, or drummy feeling/sounding snow should be avoided as well.  To avoid these slabs, stick to wind protected terrain well below the ridges and manage your slope angles.  Avoid wind affected or  wind loaded slopes over 35 degrees and utilize safe route finding and travel techniques for you and all the members of your group today.  

          

Avalanche Problem 2: Loose Dry
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The storm that rolled through over the last 48 hours left us with a cooling trend and just about 12 inches of new snow.  Leeward slopes have received much more than that and protected areas that avoided the worst of the winds will feel a LOT deeper than that no matter whether you are on a sled or skis today with our 7 day snow totals reaching just about 40 inches of snow! 

Surprisingly, we found little evidence of a storm slab yesterday in Lick Creek Canyon, the upper portion of the snowpack was unconsolidated to form a slab.  Loose/ Dry snow avalanches or sluffs were occurring on steep slopes as we skied and had occurred naturally on very steep slopes.  These sluffs were confined to the upper 25cm ( 8-10 inches) of new snow.  While there are several weak layers in the deeper snowpack, none of them showed the potential for propagation in ski cuts or in our pit tests.

Anticipate the presence of sluffs if you are skiing in steeper terrain today and don't let them surprise you or push you somewhere you don't want to go.  Sluffs can pile up deep in gullies, on benches or other terrain traps.  They can also push you into or over terrain or other areas you don't want to go.  Bottom line, travel safe and keep your eyes on your travel companions if you are venturing into terrain over 35 degrees today.

advisory discussion

Conditions are variable across the forecast area right now, our advisory is based on a small view of a limited amount of terrain this year with our reduced schedule.  PLEASE, let us know what you are seeing out there whether it is deep, stable snow or avalanche activity.   We have a very user friendly way of reporting conditions and avalanche activity on our website and WE NEED YOU TO HELP THE PAC paint a more reliable picture of the larger forecast area.  PLEASE submit observations to us, your info is invaluable to us and could save a life!

recent observations

Yesterday we toured in a protected corner of Lick Creek Canyon.  We found completely different conditions than the exposed slopes of West Mountain that we toured on Thursday.  The most surprising feature of the day was that when we had visibility we saw no evidence of a natural avalanche cycle.  We found no evidence of a storm slab either.  The common feature of our 2 days was high elevation wind.  SW winds were actively transporting snow yesterday with large plumes visible on the highest peaks.  We found large cornices and shallow wind slabs near ridgelines and some stiffer/cohesive wind slabs on wind exposed(windward) terrain below the ridgelines.  The most surprising was that we found no evidence of a storm slab on any of the aspects we traveled through yesterday.   The 8-12 inches of new snow from the last 48 hours was loose, unconsolidated and not well bonded to the snow below but lacked the ability to form a slab on the slopes we visited yesterday.   The best piece of advice to consider from this week's weather is that the more exposed and higher terrain you are in the more likely you are to find cohesive, deeper and  more sensitive wind slabs.  We also found extremely sensitive cornices on the ridgelines.  Avoid travel on heavily corniced ridgelines and make sure you know where the edge is.  

From a travel perspective, trail breaking on skis is easier than you might expect given the amount of new snow over the last week with ski penetration rarely over 30cm deep.  Off trail travel on a sled is a different story though,  you can expect to be trenching at least 2 feet deep and even deeper in protected terrain or when you are climbing.  

The Avalanche Warning has expired this morning as well.

 

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 9 deg. F.
Max. temperature in the last 24 hours: 22 deg. F.
Average wind direction during the last 24 hours: S
Average wind speed during the last 24 hours: 7 mph
Maximum wind gust in the last 24 hours: 22 mph
New snowfall in the last 24 hours: 11 inches
Total snow depth: 67 inches
weather

.SHORT TERM...Today through Sunday...A closed upper level low and
deep upper level trough along the west coast will move slowly
eastward today over southern Oregon and Idaho. This weather
pattern will produce scattered to numerous snow showers across the
region today. Satellite imagery shows several embedded smaller
circulations swirling around inside the larger low which will help
focus the shower activity. It has been snowing across much of
Nevada overnight and this activity will continue to spread
northward into extreme southern Oregon and extreme southern Idaho
on Saturday. Snow advisories have been issued for the Owyhee
mountain zone and for southern Twin Falls County where several
inches of new snow will fall. Scattered snow showers are also
expected in valley locations today, and may briefly coat the
ground with snow, but accumulation should be less than an inch in
most areas. Shower activity will diminish tonight...though some
snow showers will remain in the mountains through Sunday.

.LONG TERM...Sunday night through Saturday...Northwesterly flow
will keep temperatures below normal on Monday. Temperatures warm
quickly to near normal as an upper level ridge builds over the
Intermountain West Tuesday. Southwesterly follow aloft will bring
temperatures to near normal by Thursday. The next upper level
trough will impact the area beginning Thursday with the main bulk
of precipitation coming on Saturday. Snow level will steadily rise
through this period reaching above 5000 feet by Saturday.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Scattered snow showers after 11am. Partly sunny, with a high near 31. Wind chill values between -1 and 9. Light and variable wind. Chance of precipitation is 30%. Total daytime snow accumulation of less than one inch possible. A 20 percent chance of snow showers. Mostly cloudy, with a low around 12. Calm wind A 30 percent chance of snow showers. Mostly cloudy, with a high near 30. Light and variable wind becoming west 6 to 11 mph in the afternoon. New snow accumulation of less than one inch possible.
Temperatures: 31 deg. F. 12 deg. F. 30 deg. F.
Wind direction: Variable Calm W
Wind speed: Light Calm 6-11
Expected snowfall: Trace in. 0 in. Trace in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Scattered snow showers after 11am. Partly sunny, with a high near 22. Wind chill values between -3 and 7. Southeast wind 5 to 7 mph becoming light and variable. Chance of precipitation is 40%. Total daytime snow accumulation of around an inch possible. A 30 percent chance of snow showers, mainly before 11pm. Mostly cloudy, with a low around 10. Wind chill values between zero and 5. West northwest wind 5 to 7 mph becoming north northeast in the evening. New snow accumulation of 1 to 2 inches possible. A 40 percent chance of snow showers. Mostly cloudy, with a high near 21. Wind chill values between -1 and 9. North wind 8 to 14 mph becoming west in the afternoon. New snow accumulation of 1 to 2 inches possible.
Temperatures: 22 deg. F. 10 deg. F. 21 deg. F.
Wind direction: SE WNW then NNE N then W
Wind speed: 5-7 5-7 8-14
Expected snowfall: 1 in. 1-2 in. 1-2 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.