Avalanche Advisory published on January 19, 2018 @ 6:38 am
Issued by Dave Bingaman - Payette Avalanche Center
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The avalanche hazard is Considerable above 6000 feet today.  The combination of gusty winds from multiple points on the compass and over a foot of new snow have created new wind slabs on exposed terrain.  In addition, storm slabs of 12+ inches have accumulated on a variety of old snow surfaces.  Both of these shallow instabilities will add to the complexity of this year's snowpack including the lingering possibility of triggering large avalanches on the persistent weak layer from November.

How to read the advisory

  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

The storm that entered our area yesterday morning brought with it gusty winds that started from the Southeast and wrapped around the compass to the West during the day.  Wind speeds at Granite Mt were recorded near 30 mph.  The combination of a significant snowfall and wind will have created wind slabs on exposed upper elevation terrain.  These slabs are likely dense as a result of the warmer temperatures that we saw through the day yesterday and potentially will be easy to trigger by skiers and sledders today.  Pay attention to changes in the texture or look of the snow pack in areas that saw the direct effects of the winds and expect newly formed wind slabs on a variety of slopes today.   Cracking, or sudden changes in how deep you are traveling in the snow pack are indicators of wind slabs.   Visibility is going to be an issue today,  expect wind slabs on upper elevation terrain and avoid them by staying on lower, wind protected slopes today.  The additional load created by these wind slabs will also increase the potential of larger avalanches failing on the weak layer formed back in November especially in shallow, rocky areas that had a thinner snow pack prior to the last 2 storms.

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

Our snow pack just gained some weight, and will likely need a few days to adjust to the change.  Local Snotels reported over 1.5 inches of Snow Water Equivalent during the last 24 hours which is between 9 inches in the lower elevations and likely closer to 18 inches in the upper elevations.  This new snow fell on a variety of old snow surfaces including thick and thin crusts as well as a newly formed layer of faceted snow in shady and protected terrain. The National Weather Service is calling for additional snow fall throughout the day today which will add to the depth of storm slabs and increase the avalanche hazard.   Natural avalanches in the new snow are possible trending to likely today  on steeper slopes and human caused avalanches are definitely likely today which means you need to be cautious as you travel today.  Our November persistent weak layer is the wildcard in the snow pack,  the potential for larger avalanches either starting in this layer or starting shallow and stepping down into the November layer has risen significantly with the additional weight of storm and wind deposited snow.  Don't let your powder fever get the best of you today.  Your best and safest bet for the day is to avoid terrain steep enough to slide and be aware of steeper slopes around  or above you.  

advisory discussion

Please take the time to report any avalanche activity to the PAC.  You can click on the Submit Observations tab on the website or email us at:   Photos, aspect, elevation and depth of the avalanche are great details and help us get a good picture of what is going on in the advisory area.

recent observations

Wet slide avalanches were reported from the Northern and Southern portions of the advisory area over the last week with warm temperatures in both upper and lower elevations.  In addition, skiers on a NE slope near the & Devils triggered a large avalanche (D3)last weekend that failed on the November layer of faceted snow.  

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 20 deg. F.
Max. temperature in the last 24 hours: 33 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 13 mph
Maximum wind gust in the last 24 hours: 29 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: NA inches

.SHORT TERM...Valley rain and mountain snow showers continuing
this morning. Snow level 3000 feet MSL in Baker County to 5500
feet in Twin Falls County this morning, lowering to 2500 feet
in Baker County to 4200 feet in Twin Falls County this afternoon.
Rain showers may mix with or change to wet snow in the Treasure
and Magic Valleys but no snow accumulation is expected. However,
a winter weather advisory for snow will continue this morning
in the west central Idaho mountains for a couple more inches of
snow. Incoming upper trough will split today with the stronger
part going well south of us, and the weaker part continuing a
slight chance of snow showers in our mountains into Saturday.
Today will be quite a bit cooler than yesterday, but only cooling
to normal for mid-January. Saturday looks about two degrees
cooler than today. Finally, patchy fog will form in the valleys
tonight and Saturday morning.

.LONG TERM...Saturday night through Friday...A typical winter
pattern continues for the forecast area with several systems shown
to move across the region. However, these systems lack significant
cold air limiting snowfall potential for the lower valleys. The next
upper level trough moves quickly across SE Oregon late Sunday night
and into SW Idaho early Monday. This will be the coldest of all the
systems as snow levels sit close to 3k feet MSL for southern portions
of the CWA and below 3k MSL northward. The mountains will see 3 to
6 inches of new snow. Valleys will likely see a mix of rain/snow as
guidance remains consistent keeping surfaces temperatures at or
slightly above freezing Monday morning. The fast moving trough will
also help limit any valley snow accumulations. A brief break in the
precipitation on Tuesday as a ridge develops ahead of the next
trough. The next trough moves in Tuesday night and lasts through
Wednesday. Snow levels ahead of this system climb to near 4500ft MSL
for southern portions of SE Oregon and between 3000-3500 feet MSL
elsewhere. As the cold front with this trough pushes through
Wednesday evening, snow levels plummet back down to valley floors
with most of the precipitation ending by then. Valleys could start
as a mix of rain and snow Tuesday night but quickly change to rain
with passage of a warm front. The mountains still look very good for
snowfall with this system. Snow showers possible on Thursday with
the trough passage. Friday will be dry as another upper level ridge
develops ahead of the next upper level trough for Saturday which
looks to be a wetter and warmer system. Temperatures remain near
normal through the extended period.

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. High near 33. Southwest wind around 7 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 3 inches possible. A 20 percent chance of snow showers before 11pm. Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 18. Light south southwest wind. A 20 percent chance of snow showers after 11am. Patchy fog before 11am. Otherwise, mostly cloudy, with a high near 29. Calm wind becoming southwest around 5 mph in the afternoon.
Temperatures: 33 deg. F. 18 deg. F. 29 deg. F.
Wind direction: SW SSW SW
Wind speed: 7 Light 5
Expected snowfall: 1-3 in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Snow showers, mainly before 11am. High near 23. West wind 6 to 8 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. Mostly cloudy, with a low around 14. West southwest wind 5 to 7 mph. A 20 percent chance of snow showers. Mostly cloudy, with a high near 20. West southwest wind around 6 mph.
Temperatures: 23 deg. F. 14 deg. F. 20 deg. F.
Wind direction: W WSW WSW
Wind speed: 6-8 5-7 60
Expected snowfall: 2-4 in. 0 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.