THIS AVALANCHE ADVISORY EXPIRED ON March 11, 2020 @ 5:30 am
Avalanche Advisory published on March 10, 2020 @ 5:30 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Buried surface hoar will continue to be your main concern in the Purcells and West Cabinets on the shady side of the mountian right now. On southerly aspects pay attention to the possibility of small loose-wet slides when the sun comes out

How to read the advisory

Buried surface hoar will continue to be your main concern in the Purcells and West Cabinets on the shady side of the mountian right now. On southerly aspects pay attention to the possibility of small loose-wet slides when the sun comes out

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    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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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 it can be found about 14" below the surface, in the West Cabinets there are two layers being found in the upper 30" 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.

 

Avalanche Problem 2: Loose Wet
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Area wide we recieved a fresh dose of snow above 4,000' this past weekend. In many locations this new snow is resting on a firm and crusty surface. With mild March temperatures and sunshine we can expect this surface snow to develop small point releases on southerly aspects in steep terrain. If you are starting to see pinwheels and small surface avalanches it may be time to move into the shade or avoid high consequence terrain.

recent observations
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If you dig down into the snow on shady aspects in the timber right now 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 14" below the surface. My cohorts on the Idaho side of the West Cabinets are finding two layers of surface hoar buried in the upper 30" of the snowpack. I spent a fair bit of time poking around shady aspects in the Cabinet Wilderness last Thursday 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. 

Now that we are into March the sun really does have some heat to it when the clouds break away. It looks like we may see a fair bit of sun in the coming days and this will give us some potential for small, "loose-wet" slides in steep terrain. As always, just keep aware of whats below you if riding on sunny slopes this time of year. A small avalanche can have big consequences if it slams you into a tree or takes you off a cliff. Other potential issues to keep an eye on will be windslabs in high terrain. Yesterdays observations showed the new snow loaded into some small pillows on leeward aspects, but wasn't proving to be dense or develop much slab potential. If you are in the high alpine this week I would keep an eye out for this potential on north and east aspects near ridgelines.

 

Weather and CURRENT CONDITIONS
weather summary 
Backcountry Forecast from NWS Missoula issued:
440 AM MDT Tue Mar 10 2020

DISCUSSION: 

Northwest Montana: Sunny to partly sunny skies today and warm
temperatures across the Northern Rockies today will gave way to a
quick-moving disturbance arriving late tonight or early Wednesday
morning. This disturbance will bring a dose of snow to northwest
Montana, especially the Glacier National Park area, Flathead, and
Mission ranges. The increase in cloud cover tonight will mean
overnight low temperatures will be a little warmer, preventing
some areas from freezing overnight. Winds out of the west and 
southwest will increase tonight with the arrival of the incoming 
wave. Next chance for winter weather will be this weekend as a 
strong cold front looks to bring high winds and snow to the 
Northern Rockies by Friday.

Kootenai:

--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Wed      
Cloud Cover           60%          80%          60%      
Hi/Lo Temps           29 to 36     24 to 31     29 to 38 
Winds(mph)            SW 15G38     SW 20G38     W 14G33  
Precip Chc            0            60           70       
Precip Type           snow         snow         snow     
Liquid Amt            0.00         0.15         0.07     
Snow Ratio(SLR)       15:1         11:1         13:1     
Snow Amt(in)          0            1-5          1        

Snow Level            2000         3500         3000

 

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.