THIS AVALANCHE ADVISORY EXPIRED ON January 14, 2018 @ 7:09 am
Avalanche Advisory published on January 13, 2018 @ 7:09 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Hazard is Moderate today.  Moderate Hazard means that while the likelihood of natural avalanches has dropped today, it is still possible that we could see some natural avalanches on slopes that warm up rapidly today.  Moderate hazard also means that human triggered avalanches are possible on certain slopes today.  Play it conservative today, watch for signs of wind affect on upper elevation terrain and instabilities in the new snow that we received over the last few days.

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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This week's weather produced much needed precipitation (nearly 2 feet!) but was accompanied by winds gusting across the compass.  Wind slabs  of varying thicknesses have formed in the new snow on exposed upper elevation ridges and leeward slopes as a result.  We found windslabs forming this week on West, North and East Facing slopes.  The slabs are resting on the new snow in some areas, on older wind slabs in some areas and on the firm snow leftover from warm temperatures last week in others.  In areas where the persistent weak layer of snow above the Thanksgiving Rain Crust exists it is possible that triggering an avalanche in the relatively shallow wind slab could overload this weak layer or step down into this layer resulting in a much larger avalanche capable of propagating over a much larger area. Slopes that were protected from W/SW winds are less likely to have these slabs than areas that are exposed to the brunt of W winds. 

Patrollers at Tamarack Resort reported large wind slabs under the cornice propagating across large areas and in some areas stepping down into the deeper layers with explosives mitigation yesterday inside the boundaries of the ski resort.  They also reported that some of their terrain had released naturally in the new wind layers Thursday night. Much of the West Mountain area probably has similar conditions right now based on the prevailing winds earlier this week.  

The Northerly and East facing slopes that we toured yesterday in the Fisher and Little French Creek Drainage showed almost no signs of instability from wind slabs but these slopes were protected from the W/SW winds earlier in the week.

Pay attention to changing snow surface conditions as you get close to exposed ridges and terrain features today.  If you suddenly find yourself traveling closer to the surface or notice more firm snow below you, you are likely entering into wind affected snow.  Ripples, rounded or pillowed looking areas or cornice and wind lip formation are also visual clues that the snow has been affected by the wind.  Obvious clues like cracking in the snow surface should not be ignored today. Use safe travel tactics, cross steep areas ONE AT A TIME and be aware of subtle changes in the snow today.

Avalanche Problem 2: Persistent Slab
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Yesterday, we found a highly variable snowpack with depths ranging from a few feet to just over 6 feet.   The only thing we found in common throughout the snowpack were shallow instabilities in the new snow that lacked significant propagation potential.  Pit tests and some large cornice bombs showed us the potential for sluffing or loose, dry avalanches on steep terrain and the potential for small soft, storm slabs that were failing around 25-30 cm down from the surface.  HOWEVER:  the deeper, weak layer of faceted snow was still present above the Thanksgiving Crust at 7700 feet on an East aspect although it was not affected by our pit tests.  Closer to 8200 feet we found the faceted layer on a shallow rocky north aspect to be fairly well defined but lacked the crust below it.  It failed when we isolated our test column.  3 feet further over in the same pit we had no results where the snow was nearly 6 feet deep and the faceted layer proved to be unreactive even under hard force.  Thursday we found the Thanksgiving rain crust/facet combination to be extremely reactive in the Lick Creek Drainage on an East facing slope near 7700 feet.

The bottom line is that the snowpack is still wildly variable on different aspects and in different elevations and areas.  The weak layer of faceted snow above the Thanksgiving Rain Crust is still persisting in the snow pack on nearly every aspect. The strength of this layer is wildly variable with stability results ranging from confidence inspiring to very concerning have been documented this week.  The potential for a shallow avalanche stepping down into this layer also exists in areas where the weak layer is more buried less deeply. Variability is the name of the game right now and that means there is no yes or no answer about which slopes are safer to travel on.  Cautious, informed decision making is mandatory for safe travel right now. The potential of triggering an avalanche in this layer is like rolling the dice right now and the consequences are significant. See this short video for a better look at what we found in our pit tests on Thursday.  This layer also has been creating problems in areas adjacent to the PAC advisory area;  Mores Creek Summit near Boise experienced a significant natural avalanche cycle on the persistent weak layer Thursday night.  

 

 

Avalanche Problem 3: Loose Wet
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Chalk it up to climate change or just a warm storm cycle but temperatures are going to rise today and over the next few days.  The combination of rapid temperature increases and new snow is the perfect recipe for wet/loose avalanches on steep, sun affected or lower elevation slopes.  The hazard of wet/loose activity will follow the sun and increasing temperatures later in the day.  Signs of wet snow instabilities are increasing roller ball activity and trees starting to shed their snow.  Expect this to be more likely near steep, rocky terrain and continue to increase with temperatures in the mid to upper 30's forecasted for Sunday and Monday.

advisory discussion

Please report any avalanche activity that you see or trigger, it helps us gain a much better picture of what is happening over a larger area.  You can click on the observations tab on our web page or email us at: forecast@payetteavalanche.org  Information about the aspect, elevation, depth, trigger and location with or without photos is easy to submit on our web based observations page and helps us a lot.

 

recent observations

We toured from Fisher Creek Saddle yesterday and found a much less threatening snowpack than in other areas.  Depths were variable and the persistent weak layer was variable depending on the depths and elevations where we dug.  Shallow instabilities in the upper snowpack were found in the form of soft, mostly unconsolidated storm slabs on East and North aspects but were lacking in their potential to propagate.  Compression test scores were in the moderate to high ranges(CT 14 at 20cm(E aspect near 7700 ft) and a CT 24 at 35 cm on a more windloaded northerly slope above 8000ft.) Sledding and skiing conditions were phenomenal with soft, deep snow found on all aspects.  Coverage is improving too with our most recent storm laying down bushes and filling in around rocks and downed logs.  

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 24 deg. F.
Max. temperature in the last 24 hours: 26 deg. F.
Average wind direction during the last 24 hours: WNW
Average wind speed during the last 24 hours: 2 mph
Maximum wind gust in the last 24 hours: 4 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: 61 inches
weather

SHORT TERM...Today through Sunday night...Limited lingering
moisture may still generate some snowfall across the West Central
Mountains this morning, though snowfall will continue to dissipate
through the morning. With drying expected, fog formation remains
the primary challenge of this forecast period. Patchy fog is
possible across the valley locations this morning, with pockets of
dense fog around McCall, ID. Most fog should lift by the late
morning hours. Widespread dry conditions expected by this evening,
with the inversion forming in the Treasure and Magic Valleys.
Another, more favorable, round of fog will be possible Sunday
morning with best formation looking to be in the valley from
around Mountain Home, ID west to Baker City, OR. Again fog is
generally expected to lift by the late morning hours, but possible
to return Sunday evening. Otherwise, generally light wind expected
with some periods of potentially gusty wind in the Western Magic
Valley on Sunday. Temperatures expected to remain above normal
through the weekend.

.LONG TERM...Monday through Friday...Upper level ridge will
continue to impact region through Tuesday morning. A weak cold front
will move through the region on Wednesday morning, bringing a brief
round of precipitation, with rain below 4500-5500ft and mountain
snow. Weak ridging returns on Thursday, bringing strong southwest
flow aloft and continued warm temperatures. A cold front is expected
to slowly track across SE Oregon and southern Idaho Thursday
afternoon into Friday morning, bringing widespread precipitation
with snow levels around 4500ft in Baker County to 6500ft toward the
NV border with the bulk of the precipitation. Snow levels fall to
the valley floors by Friday evening, as the precipitation tapers
off. Snow showers will continue over the mountains into Saturday.
Temperatures cool to near normal or slightly below normal for
Saturday.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Mostly cloudy, with a high near 38. Light south wind Patchy fog. Otherwise, partly cloudy, with a low around 25. Calm wind. Mostly sunny, with a high near 38. Calm wind.
Temperatures: 38 deg. F. 25 deg. F. 38 deg. F.
Wind direction: S 0 0
Wind speed: light Calm Calm
Expected snowfall: 0 in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: A 20 percent chance of snow before 11am. Mostly cloudy, with a high near 32. West northwest wind 3 to 6 mph Partly cloudy, with a low around 27. Calm wind becoming southwest around 5 mph after midnight. Mostly sunny, with a high near 35. South southwest wind around 7 mph.
Temperatures: 32 deg. F. 27 deg. F. 35 deg. F.
Wind direction: NW SW S/SW
Wind speed: 3-6 5 7
Expected snowfall: in. in. 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.