THIS AVALANCHE ADVISORY EXPIRED ON February 24, 2018 @ 5:13 am
Avalanche Advisory published on February 23, 2018 @ 5:13 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

The wind slabs and weak layers under last weekends' storm snow have strengthened significantly this week. The potential still exists to trigger an avalanche in these variable wind deposits and stubborn weak layers. Use caution in steep terrain, particularly on Southwesterly aspects.  Weather forecasts are predicting significant storm snow Saturday thru Sunday so expect avalanche danger to potentially rise with new snow and wind.

How to read the advisory

The wind slabs and weak layers under last weekends' storm snow have strengthened significantly this week. The potential still exists to trigger an avalanche in these variable wind deposits and stubborn weak layers. Use caution in steep terrain, particularly on Southwesterly aspects.  Weather forecasts are predicting significant storm snow Saturday thru Sunday so expect avalanche danger to potentially rise with new snow and wind.

2. Moderate

?

Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

?

Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

?

Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

The cold front that rolled into the area on Sunday the 18th  brought with it strong Northeast winds that scoured the new snow off of exposed terrain and deposited the freshly fallen snow onto Southwesterly aspects.  These windslabs have gained significant strength over the week; but, they are still reactive in isolated locations. (see photo)  These slabs vary greatly in thickness, distribution and sensitivity.  Use caution on Southwesterly faces and expect to see wind-loading in atypical locations as you travel.

Cause and effect.

   

East side.  Heavily scoured slope at 6,000'.                                           West side.  Wind slab release 6-8" thick at 5,500' under steep roll.

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

Last weekends storm left us with 16-20" of fresh snow at most locations across the Kootenai. This snow has gained significant strength over the week; but, triggering an avalanche in this most recent slab layer is still a possibility. Stability tests are revealing two weaknesses: facets and graupel on the February 4th rain crust and a density change between the old snow and the recent storm snow. Triggering this layer will likely take a lot of force, or possibly finding a thin spot in the upper snowpack. This possibility is enhanced due to the variability in the upper snowpack created by the strong Northeasterly winds. On Northeast aspects above treeline it is unlikely you will find any of the recent storm snow as the winds Sunday managed to strip the snow down to the most recent crust layer.

advisory discussion

Support your local avalanche forecasting center and your local  brewery on March 8th by joining us for the "Brews For Benefits" at the Cabinet Mountain Brewery.  Cabinet Mountain Brewery will be donating $1 for every beer sold to the Idaho Panhandle Avalanche Center.  Unleash your inner altruist and join us for a beer from 5-8 P.M.

recent observations

Observations taken from the Keeler Rattle area revealed a stabilizing snowpack following last weekends storm and strong winds.  The weaknesses in the upper snowpack are still there but showing significant gains in strength and stability.  We observed some small natural releases on loaded aspects in the steepest terrain as well as a failure initiated by ski-cut shown in the above photo.  Looking forward into Saturday and Sunday the weather forecasters are gaining confidence in a series of storms that are predicted to bring in some decent accumulations and wind into the area. If these storms materialize riders can expect the avalanche danger to rise and storm slabs to become a problem. On Northeasterly aspects this new snow will fall on the freshly exposed crust layer which will provide an excellent sliding surface at elevations above treeline.  Pay close attention to these weather systems going into the weekend!

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
510 AM MST Fri Feb 23 2018

DISCUSSION:  
The first in a series of weather systems to bring snow to the
Northern Rockies will be wrapping up this morning over the
Bitterroot Range, with accumulations generally less than 3 inches
across north central Idaho and southwest Montana.

The second weather system will concentrate light to moderate snow
at mountain pass elevations and higher along the ID/MT border
Saturday morning through late Saturday evening. Snow accumulations
6 to 10 inches for passes and high terrain will be common.

The third weather system overhead Sunday morning through Monday
morning will be accompanied by a relatively strong Pacific 
moisture surge. This third system is anticipated to produce the
most significant high elevation snowfall for most mountain ranges
(8 to 12 inches for Cabinet, Clearwater, Bitterroot Ranges). Wind
may be a complicating factor as well, with relatively cold air 
following the snowfall. Also, wind over passes along the 
Continental Divide may decrease visibility at times in blowing 
snow.

Continued weather systems every 2 to 3 days are anticipated to
move over the region through the following weekend. Snow amounts
for each of these systems appear fairly modest, but the increasing
sun angle should moderate temperatures over time.


Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           40%          90%          75%      
Hi/Lo Temps           14 to 22     7 to 12      21 to 28 
Winds(mph)            W 11G24      SW 12G25     W  7     
Precip Chc            0            80           80       
Precip Type           snow         snow         snow     
Liquid Amt            0.00         0.17         0.13     
Snow Ratio(SLR)       20:1         20:1         20:1     
Snow Amt(in)          0            3-5          2-5      
Snow Level            0            0            0        
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.