THIS AVALANCHE ADVISORY EXPIRED ON February 20, 2019 @ 4:34 am
Avalanche Advisory published on February 19, 2019 @ 4:34 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

The area has been exposed to strong winds blowing from multiple directions the last few days at all elevations. With ample loose snow available for transport this has created windslabs directly below ridgelines and in steep, cross loaded terrain that is open and exposed to the winds. Use caution in these terrain features.

How to read the advisory

The area has been exposed to strong winds blowing from multiple directions the last few days at all elevations. With ample loose snow available for transport this has created windslabs directly below ridgelines and in steep, cross loaded terrain that is open and exposed to the winds. Use caution in these terrain features.

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: Wind Slab
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The winds have blown from all directions this past week.  On Saturday I observed multiple "natural crowns" and one small avalanche on steep, south facing terrain that had been cross-loaded by southwest winds. Some of the crowns were as low as 4,500' in elevation and they all released vertically on ribs running adjacent to cross-loaded gullies. These windslabs have become pretty stiff with the recent strong winds and may be difficult to trigger but should be treated with caution.  Expect to find these slabs on any aspect or elevation in steep terrain.  Steep and open terrain with cross-loaded gullies are where a rider may find trouble this week. See photos below.

Avalanche Problem 2: Persistent Slab
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Observations taken on Flatiron last week still show that the Persistent weakness in the Purcell Range may be an issue. Stability tests were failing with moderate force and showing the potential to propagate on a weak layer buried 32" below the surface. I would continue to pay attention to this possibility while riding in northerly aspects between 5,000' and 6,000'. Obvious clues such as collapsing and shooting cracks should alert you to the presence of this weak layer. The best way to avoid triggering this layer will be to avoid steep convex rolls in suspect locations.

advisory discussion

Last weeks storm snow has settled well with time and the moderate temps late last week and is unlikely to cause a problem at this point. The big issue right now is the wind. On Saturday in the Cabinets it was cranking out of the south-west and creating alot of cross-loading on southerly faces and I was able to trigger isolated slabs below ridgeline on NE aspects. (see observations) On Sunday the area was blasted by more north-east winds with the latest cold front. Travels Monday revealed that all aspects experienced some degree of wind effect all the way to drainage bottoms. Many of these slabs are very firm at this point and will likely be difficult to move but I would definetly use caution in steep terrain and chutes where the snow loaded in.

The "persistent slab" problem is unlikely to go away soon with the cold temperatures in the Purcell Range. Continue to keep it in mind when selecting terrain and pay attention to the obvious clues.  Have fun and stay safe out there!

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
410 AM MST Tue Feb 19 2019

DISCUSSION: Widespread light to moderate snow will return to the
region this evening, and continue through much of the day on 
Wednesday. Breezy southwesterly winds will turn more northeasterly
late Wednesday and Thursday with another reinforcing shot of a 
modified arctic airmass. This arctic isn't expected to be as 
strong as the previous ones early this month. The Northern Rockies
will remain under a broad trough of low pressure the rest of the 
week going into the weekend, with a series of Northern Pacific 
systems bringing more snow.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Wed      
Cloud Cover           70%          90%          90%      
Hi/Lo Temps           14 to 20     9 to 13      20 to 27 
Winds(mph)            SW 11G24     SW 10G26     NE  8    
Precip Chc            80           90           50       
Precip Type           snow         snow         snow     
Liquid Amt            0.03         0.11         0.03     
Snow Ratio(SLR)       20:1         20:1         20:1     
Snow Amt(in)          0-1          2-4          0-1      
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.