THIS AVALANCHE ADVISORY EXPIRED ON March 7, 2020 @ 5:20 am
Avalanche Advisory published on March 6, 2020 @ 5:20 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Pay attention to steep and open timber on the shady side of the mountain right now. This where you may be able to trigger an avalanche on the buried surface hoar that is lurking out there. 4-9" of new snow is forecast to fall by Saturday afternoon above 5,000'. Pay attention to how this new snow is setting up on Saturday and Sunday and be alert to the potential for thin storm slabs to develop.

How to read the advisory

Pay attention to steep and open timber on the shady side of the mountain right now. This where you may be able to trigger an avalanche on the buried surface hoar that is lurking out there. 4-9" of new snow is forecast to fall by Saturday afternoon above 5,000'. Pay attention to how this new snow is setting up on Saturday and Sunday and be alert to the potential for thin storm slabs to develop.

2. Moderate

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

2. Moderate

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

1. Low

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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: Persistent Slab
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  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
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We have a well developed layer of surface hoar out there that can be found on shady aspects above 5,000' in elevation. In the Purcells I was finding it about 8" below the surface, in the West Cabinets there are two layers being found in the upper 18" of the snowpack. In the East Cabinets I can't find any, despite a lot of looking for it! It is gaining strength and is showing a low likelihood of propagating into an avalanche at this time; however, I wouldn't fully trust it just yet. Your likely spots to have trouble are very steep openings or convex rolls in the timber where the surface hoar was preserved prior to the last snowfall. There are also some weak sugar layers above and below the February 1st rain crust in the Purcell Range that I would continue to keep in mind, These layers are also trending towards a more stable state as the mild temperatures heal the snowpack.

recent observations
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The weather has been pretty mild lately, and that has been good for creating a stable snowpack. Overall things are looking pretty good out there. Most of the terrain I have been on this week is pretty firm on the surface, wind buff, breakable crust and the occasional powder pocket in well protected timber. As I mentioned above we have a weak layer that is very pronounced under our last snowfall. If you dig down into the snow on shady aspects in the timber you will possibley find a thin grey streak in the upper snowpack. This layer of surface hoar was found Monday at Flatiron and the flakes were 8mm tall, buried 7-8" below the surface. My cohorts on the Idaho side of the West Cabinets are finding two layers of surface hoar buried in the upper 18" of the snowpack. I spent a fair bit of time poking around shady aspects in the Cabinet Wilderness and was unable to find any buried surface hoar in that location. Stability tests show this layer is resistant to propagation and continuing to gain strength. Keep your hackles raised if you are riding in steep timber on northerly aspects until this layer is fully healed. In terrain that has been exposed to the wind and sun, this surface hoar was likely destroyed before it had the chance to become a problem, if you are looking to play in steeper terrain then these south and westerly aspects will be safer choices right now.

Going into the weekend we have 4-9" inches of snow predicted at the upper elevation bands. This snow will likely come in on the dense and heavy side. It will also be falling on some surfaces that will be difficult to stick to, such as wind crusts and graupel. Keep on your toes Saturday and Sunday as this new snow come in. Weakness will be easy to spot on the surface of the snowpack. If you observe fresh avalanhces or cracking in steep terrain then it is time to dial back your terrain selection to more conservative ground.

Weather and CURRENT CONDITIONS
weather summary 
Backcountry Forecast from NWS Missoula issued:
400 AM MST Fri Mar 6 2020

DISCUSSION: 
Northwest Montana: It will be warmer than average today and there
could be a passing shower or sprinkle in the mountains. Spotty
areas of steady precipitation is expected to develop later this 
evening and tonight with the snow level around 5,000 feet. A cold
front will move through by Saturday afternoon, which will
reinvigorate mountain snow showers that will linger into Sunday.
Confidence is low, but a few week disturbances could trigger more
snow showers on Monday. Daytime highs will generally be near
average while clearing at night will allow good cooling. 

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           90%          95%          100%     
Hi/Lo Temps           33 to 41     27 to 32     29 to 36 
Winds(mph)            SW 11G26     SW  8G23     SW  9G22 
Precip Chc            40           90           100      
Precip Type           snow         sno/fzra     snow     
Liquid Amt            0.01         0.25         0.36     
Snow Ratio(SLR)       10:1         13:1         13:1     
Snow Amt(in)          0            3-4          4-5      
Snow Level            4500         4500         4000

 

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.