THIS AVALANCHE ADVISORY EXPIRED ON March 3, 2018 @ 7:11 am
Avalanche Advisory published on March 2, 2018 @ 7:11 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The avalanche hazard is HIGH on upper elevation slopes where a combination of new snow and strong winds have created very sensitive wind slabs.  A very tender storm slab exists on wind protected slopes where over a foot of new snow has fallen in the last 2 days.  Human triggered avalanches ranging in size from a few inches to over 2 feet are very likely today.  Avoid steep wind affected terrain and all slopes over 35 degrees.

How to read the advisory


  • Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
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South winds howled yesterday and had plenty of light density snow to pick up and move around.  Ridgetop winds peaked last night with gusts approaching 50 mph adding even more snow to our wind slab problem.  Sensitive wind slabs began forming early yesterday and increased in size through the day and overnight.  You may encounter soft or hard slabs of up to or possibly even larger than 2 feet deep today.  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. 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 and manage your slope angles.  Avoid slopes over 35 degrees and utilize safe route finding and travel techniques for you and all the members of your group today.  These conditions will likely increase through the early part of the day today as we receive additional snow and wind, expect these sensitive slabs to linger over the weekend even after the storm moves out of the area.

See photo below for a small pocket of wind slab that we were able to easily trigger on skis yesterday.  Also here is a short video of the conditions we have encountered earlier this week and yesterday in the backcountry north of Tamarack Resort.

Avalanche Problem 2: Storm Slab
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The storm that began yesterday brought with it just over .5 inches of Snow Water Equivalent which turned out to be just under a foot of snow in the middle elevations.  In addition to the wind that accompanied the storm, we also saw  a spike in the temperture from the near 0 range earlier this week to a high of 33 at 6700 feet last night.  These factors created a very sensitive storm slab that we were able to trigger in small pockets of steep terrain and had already began to fail naturally through the day yesterday.  With periods of heavy snow through the night, several rounds of grauple and additional snowfall predicted this morning, expect to see shallow natural avalanches in many areas today.  Human triggered avalanches are very likely today.  In the upper elevations, expect this slab to be deeper and in some areas resting on a layer of faceted or weaker snow below.  Conditions today are going to be some of the most sensitive of the year, plan your routes accordingly and avoid steep terrain today.  

Loose/dry avalanches or sluffs are also very likely in steep terrain.  Anticipate a fair amount of moving snow on all steep terrain today and don't allow yourself to get surprised in confined terrain, terrain with high consequences or terrain traps.

advisory discussion

Please take the time to report any avalanche activity to the PAC website.  We rely on your observation to give us a better picture of the conditions across our advisory area.  All you have to do is click the observations tab on the forecast page and fill out a few questions in the menu.  Medium or lower resolution photos can be added and it only takes a few seconds.  The info is valuable to us and may help save a life.

recent observations

Yesterday we toured the backcountry north of Tamarack Resort.  Wind was the big factor and wind slab were forming and increasing in size throughout the day.  A very sensitive storm slab was also growing through the day with the addtion of up to a foot of new snow.  We were able to easily trigger small pockets of steep terrain and produce avalanches in both the wind affected and the wind protected terrain.  We were also able to trigger small storm slab avalanches remotely as we skied near steep rollovers and along the edges of gullies.  

In addition to the small test slopes we were able to trigger, there was a skier triggered slide reported on steep, northerly terrain that was being rapidly loaded yesterday morning.  By the time we heard about it, most of the crown was filled in and the debris was being covered quickly.

 

See the video for a quick overview of the conditions and a couple of pictures from our day yesterday.  The pit photo shows a deeper layer of concern that release in the moderate category below the storm slab.  While unlikely, it is possible that an avalanche triggered in the new snow could potentially step down or propagate into this deeper layer creating a larger and more dangerous slab.

 

 

 

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 21 deg. F.
Max. temperature in the last 24 hours: 23 deg. F.
Average wind direction during the last 24 hours: S
Average wind speed during the last 24 hours: 15 mph
Maximum wind gust in the last 24 hours: 47 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: 58 inches
weather

.SHORT TERM...Today through Saturday...Current storm is wrapping
up over SW Idaho this morning. Lower elevations will continue to
see gusty winds and rain with heavy snow continuing in the
mountains through midday. The precipitation tappers to showers in
the mountains this afternoon, with valleys drying out. Southeast
Oregon zones will be dry and breezy today as the storm works
eastward. Dry and cold conditions tonight with the area positioned
between the exiting storm and the trailing main low. Clouds and
precipitation chances increase across far southeast Oregon
Saturday morning and to much of the area during the day Saturday
as the low moves inland. The focus of shower development will be
in the mountains with this system. While the air mass will be
cold enough for snow to the lowest valley floors, accumulation
will be limited to sites above 4k feet. Temperatures remain cold
through Saturday running 10-15 degrees below normal.

.LONG TERM...Saturday night through Thursday...The upper level low
remains over the region through Sunday bringing chances of showers
for higher elevations. Snow levels remain at valley floors so any
precipitation will be in the form of snow. An upper level ridge
follows the low and will bring more seasonal temperatures and
drier conditions through Wednesday.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: Snow showers, mainly before 11am. Temperature falling to around 14 by 1pm. South wind 8 to 11 mph. Chance of precipitation is 90%. Total daytime snow accumulation of less than one inch possible. Partly cloudy, with a low around 10. Wind chill values between zero and 5. South wind 5 to 8 mph becoming calm in the evening. A 30 percent chance of snow showers after 11am. Partly sunny, with a high near 29. Calm wind becoming south around 5 mph in the afternoon. New snow accumulation of less than a half inch possible.
Temperatures: Falling to 14 deg. F. 10 deg. F. 29 deg. F.
Wind direction: S S S
Wind speed: 8-11 5-8 5
Expected snowfall: < 1 in. 0 in. 1/2 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Snow showers, mainly before 11am. High near 20. Wind chill values between -1 and 5. Breezy, with a south southwest wind 16 to 21 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 3 to 5 inches possible. A 20 percent chance of snow showers before 11pm. Partly cloudy, with a low around 8. Wind chill values between -5 and zero. South southwest wind 10 to 14 mph. A 30 percent chance of snow showers after 11am. Partly sunny, with a high near 18. Wind chill values between -5 and 5. South wind 7 to 9 mph. New snow accumulation of less than a half inch possible.
Temperatures: 20 deg. F. 8 deg. F. 18 deg. F.
Wind direction: S/SW S S
Wind speed: 16-21 10-14 7-9
Expected snowfall: 3-5 in. 0 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.