THIS AVALANCHE ADVISORY EXPIRED ON January 22, 2020 @ 5:48 am
Avalanche Advisory published on January 21, 2020 @ 5:48 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Stable snowpack conditions will be found across the area on Tuesday. By Tuesday evening anticitpate the Avalanche Hazard to rise as modest amounts of storm-snow are forecast to fall Tuesday afternoon and evening. Thin storm slabs will likely develop and slide easily on the existing snow surface by Wednesday. Pay close attention to south and west aspects going forward where there is now a crust layer at all elevations.

How to read the advisory

Stable snowpack conditions will be found across the area on Tuesday. By Tuesday evening anticitpate the Avalanche Hazard to rise as modest amounts of storm-snow are forecast to fall Tuesday afternoon and evening. Thin storm slabs will likely develop and slide easily on the existing snow surface by Wednesday. Pay close attention to south and west aspects going forward where there is now a crust layer at all elevations.

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

There is a consistent weak spot in the snowpack approximately 1 foot below the surface that sits under the week-old storm snow interface. It is unlikely to cause a problem moving forward and continues to strengthen with time. This layer shows up consistently across the area in compression tests but shows very-low likelihood of propagation or triggering an avalanche.

advisory discussion

Early last week the area started out with significant wind loading and storm slab issues and those problems have all settled down and left us with a very stable snowpack on Monday. Yesterdays results and observations all inspired more confidence in our snowpacks strength. The only consistent failure I have been seeing is in the interface under the last storm snow but it is not a big concern as it is unlikely to propagate and has gained alot of strength with a week of mild temperatures. Some of the deeper weak layers that we have been tracking all season consist of the November 19th rain crust  and buried surface hoar from early January. The crust layer is still easy to get to in the thin snowpack of the Purcell Range but is highly unlikely to fail without a significant weather change such as a rain on snow event. I have not been able to find the buried surface hoar layer out there this past week despite extensive effort. It is deep and likley smashed by the multiple storm events we have seen in the past couple of weeks.

My concern right now is moving forward into Wednesday. On Monday we found crust layers on south and west aspects in open terrain and much of the shaded terrain had a very small layer of surface hoar growing on the snowpack. This will cause us some problems by Wednesday morning. Discussions with the Weather Service indicate that we can expect dense snow to fall mostly after mid-night at upper elevations in the East and West Cabinets. Between 4-8" will likely be the case with higher amounts on the highest peaks. It's not alot of snow; but, it's enough to take you for a ride and I expect it to be pretty reactive with the current bed surface that it will be resting on. The good news is that these surface instabilities will be easy to spot as you travel and will likely show themselves as you travel around. So, use caution on Wednesday and avoid steep terrain if you are seeing any signs of slab development, natural avalanches or cracking underfoot as you travel around.

The other problem we may see in the coming week will be temperature related. It appears that our "January Thaw" is coming and I would also anticipate the possibility of "loose-wet" avalanches below 5,000' later in the week. With a little new snow on a melt-freeze crust this problem will be most reactive on south and west aspects.

We observed multiple avalanche crowns yesterday that were all older and mostly buried by the last storm cycle. The biggest one on Bockman Peak can be seen in this photo. It released at about 7,000' and stepped down to a deeper layer on the left flank.



Big thanks to all of you that showed up for the "Intro to Avalanches" class on Friday and Saturday!!

 

Weather and CURRENT CONDITIONS
weather summary 
Backcountry Forecast from NWS Missoula issued:
340 AM MST Tue Jan 21 2020

DISCUSSION:  
NORTHWEST MONTANA: Overall a warm weather pattern continues into
next weekend. Light, nearly continuous precipitation will continue
through most of the week with the heaviest amounts tonight and
then Thursday night to a lesser degree. Snow levels will peak just
below 5,000 feet Wednesday night causing some light rain or
drizzle on the mid-slopes and dense snow with low snow ratios at
the higher elevations. Most precipitation will fall in the
Kootenai-Cabinet region with much less in the Glacier Park region.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Wed      
Cloud Cover           75%          95%          95%      
Hi/Lo Temps           29 to 35     22 to 28     26 to 33 
Winds(mph)            S 14G32      SW 23G40     SW 18G37 
Precip Chc            90           70           70       
Precip Type           snow         snow         snow     
Liquid Amt            0.16         0.29         0.09     
Snow Ratio(SLR)       15:1         16:1         16:1     
Snow Amt(in)          2-5          4-14         1-6      
Snow Level            3500         3000         2000
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.