THIS AVALANCHE ADVISORY EXPIRED ON January 27, 2018 @ 5:52 am
Avalanche Advisory published on January 26, 2018 @ 5:52 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Expect to find sensitive windslabs on leeward terrain (north and east aspects) directly below ridglines above 5,000' and in cross-loaded terrain that has been affected by southwesterly winds.  These slabs have the potential to thicken and increase in sensitivity going into the weekend.  In exposed alpine terrain above 6,000'  new storm snow will also cause concern as the incoming weather brings more load to the snowpack.

How to read the advisory

Expect to find sensitive windslabs on leeward terrain (north and east aspects) directly below ridglines above 5,000' and in cross-loaded terrain that has been affected by southwesterly winds.  These slabs have the potential to thicken and increase in sensitivity going into the weekend.  In exposed alpine terrain above 6,000'  new storm snow will also cause concern as the incoming weather brings more load to the snowpack.

3. Considerable

?

Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

?

Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

?

Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Yesterdays travels in the Eastern Cabinets revealed the development of windslabs on leeward terrain above 5,000'.  These slabs were isolated to areas directly below ridgeline features and high alpine terrain that has been cross-loaded by strong south-westerly winds.  These slabs were cracking under foot in areas that were highly exposed to the wind but they were resistant to actually moving down the hill or fully propagating in stability tests.  This avalanche problem would be a serious concern for anyone venturing into the higher and more open alpine terrain above the 6,000' elevation where there is more exposure to the wind and deeper storm snow.

     

Photo at 6,000' showing wind scoured ridge and obvious loading on north aspects.      Cracking in windslab directly below ridgeline.  Resistant to movement but very cohesive.

Avalanche Problem 2: Storm Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

This weeks storm snow came in very warm and wet.  The storm slowly cooled off and left a layer of fresh snow that bonded well below 6,000' as the snowline descend back down the hill.  This effectively left a fairly stable scenario in the new storm snow at lower elevations.  Above this elevation where it fell purely as snow we have higher storm snow totals and some weak interfaces where it has not yet bonded to the previous layer of snow.  There are also some layers of graupel buried in isolated locations within the old snow that will  add to the potential of triggering an avalanche.  If the current weather forecast pans out we can expect this problem to become more of a threat going into the weekend as more snow is in the forecast.  



 

Avalanche Problem 3: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

There are still some persistant weak layers in the snowpack.  The one most likely to be a threat involves a thin layer of facets that is overlying the crust that developed during the warm spell on January 18th.  It is not proving to be reactive in stability tests but it is still there and has a very clean sheer.  This problem is unlikely to be triggered by a rider but the potential is there if one was to find a thin spot in the snowpack or if the weather conditions cause an increase in stress on this layer.  Rapid increase in load or rising temperature could bring this layer to life.  Just remember that rapid changes in weather often cause rapid changes in snow stability.  This is worth keeping in mind as the "Backcountry Weather Forecast" is predicting the possibility of rising temperatures on Sunday and Monday.

advisory discussion

Friday night (January 26th) at 7P.M.  Libby David Thompson SAR Barn. 

Free "Intro to Avalanches" course.

See you there!

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
400 AM MST Fri Jan 26 2018
DISCUSSION: Another surge of moisture will be moving into the
Northern Rockies this morning and afternoon, that will bring more
accumulating snow to the mountains and valleys through this
evening. Some of the snow showers have the potential to produce
intense snow rates. Gusty westerly winds will also accompany the
snow throughout the day. Light to moderate snow will continue
through the overnight hours.

An active pattern will remain over the Northern Rockies through
the weekend and it will produce more mountain snow. Snowlevels 
will begin to rise on Sunday, and especially Monday, when they 
should rise up to 5000 feet.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           85%          85%          95%      
Hi/Lo Temps           25 to 29     17 to 22     27 to 31 
Winds(mph)            SW 14G29     SW  9G24     SE  6    
Precip Chc            70           60           90       
Precip Type           sno/shr      snow         snow     
Liquid Amt            0.17         0.10         0.27     
Snow Ratio(SLR)       17:1         13:1         17:1     
Snow Amt(in)          2-7          1-3          4-7      
Snow Level            1500         1500         1500     
Disclaimer

Avalanche conditions change for better or worse continually. Backcountry travelers should be prepared to assess current conditions for themselves, plan their routes of travel accordingly, and never travel alone. Backcountry travelers can reduce their exposure to avalanche hazards by utilizing timbered trails and ridge routes and by avoiding open and exposed terrain with slope angles of 30 degrees or more. Backcountry travelers should carry the necessary avalanche rescue equipment such as a shovel, avalanche probe or probe ski poles, a rescue beacon and a well-equipped first aid kit.  For a recorded version of the Avalanche Advisory call (208)765-7323.