THIS AVALANCHE ADVISORY EXPIRED ON February 9, 2019 @ 5:12 am
Avalanche Advisory published on February 8, 2019 @ 5:12 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

We continue to see reactive surface hoar buried 2' below the surface on sheltered (north and east) aspects between 5,000' to 6,000'. These slabs will be difficult to trigger but will cause large avalanches if triggered. High alpine terrain will harbor thin and soft windslabs in steep, cross-loaded chutes and below ridgelines. In steep terrain (over 40°) loose snow will slough easily and may be dangerous in areas where cliffs or trees may cause bodily harm. 

How to read the advisory

We continue to see reactive surface hoar buried 2' below the surface on sheltered (north and east) aspects between 5,000' to 6,000'. These slabs will be difficult to trigger but will cause large avalanches if triggered. High alpine terrain will harbor thin and soft windslabs in steep, cross-loaded chutes and below ridgelines. In steep terrain (over 40°) loose snow will slough easily and may be dangerous in areas where cliffs or trees may cause bodily harm. 

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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The magnum sized surface hoar that we buried back in mid January is still there. At the lower elevations the weak layers have healed or become "bridged" by the latest crust layer. Monday we began to feel collapsing and cracking in that narrow band of elevation between 5,500' and 6,000'. Multiple extended column tests revealed clean and snappy shears with moderate to hard force at these elevations. Observations submitted from Flatiron on Thursday showed a persistent weakness as well that is still propagating in stability tests. It will likely be difficult to trigger; but, there is 1-2 feet of cohesive slab on top of our buried weak layers and it will create a destructive slide if you find that sweet spot.  Short video of Mondays pit here⇒ https://youtu.be/Ve__9WWfYys



Mid January surface hoar layer. On NE aspect, E. Cabinets@ 5,800'. February 4th.       FLatiron February 7th. Propagating with moderate force.

Avalanche Problem 2: Loose Dry
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The cold front that entered the area last weekend left us with 8-10" of very loose, dry and cold snow on the surface at treeline and above. Weather forecast is predicting more light snow will arrive Friday through Saturday so we can expect this problem to stick around and even rise a bit. In most areas at these elevations it is poorly bonded to the old snow surface and was sloughing easily in terrain steeper than 40°. The big thing here is to pay attention when going into steep terrain and plan ahead, a quick ski cut will likely clean this loose snow out pretty quick. There is enough surface snow to entrain a rider and drag them over a cliff band or trees in steep terrain. Don't be that guy!



Loose dry sloughing in steep terrain. East Cabinets @ 6,000' and above.

Avalanche Problem 3: Wind Slab
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Yesterday in the southern end of the Cabinets we observed steady (10-15mph) westerly winds above 6,500' that were creating thin soft slabs on easterly aspects and steep, cross-loaded gullies. The weather predictions are calling for strong east winds this weekend as more cold air pushes over the divide. This will spread the wind slab problem onto all aspects on terrain above treeline. The highest opportunity to trigger one of these slabs will be in terrain where last Sundays snow fell on firm and crusty surfaces (wind and sun crusts).  It is poorly bonded to these surfaces and will trigger easily, pay attention to changes in snow surface density as you travel.



Thin, soft wind slabs developing on East aspects below ridgelines.

advisory discussion

On February 7th we travelled into the southern end of the Cabinets via Rock Creek. Our pit results were pretty boring and we were able to find weaknesses under the last storm snow as well as buried surface hoar; but, they were not propagating in stability tests. Observations submitted from Flatiron Mt. showed that we still have a "persistent slab" problem that has potential to propagate into a slab avalanche at mid elevations on sheltered aspects. Thanks for the Obs Cass!!

Monday we travelled into the East Cabinets expecting to find nasty wind slabs and found absolutely zero sign of wind. This baffled me as a cold front generally will hammer the mountains with northeasterly winds. 

Here's what we did see! Warm temperatures from last Friday and Saturday did a good job of breaking down our latest batch of surface hoar before more snow came into the area and this will bode well for future stability. There was a firm supportive crust under foot up to about 5,000' with 6" of new snow on top of it. Between 5-6,000' on Northeasterly aspects is where we are still finding the layer of buried surface hoar from mid January. Experienced some collapsing and "whumpfing" at this elevation and pit results revealed it is indeed still there and harboring the potential to wreck your day if you trigger it. Pay attention to these signs and this "mid-elevation" band of instability, it loves to breed complacency and surprise unsuspecting riders. Above this elevation the new snow fell on pretty firm surfaces, it is still very light and loose and we found no signs of slab development in the new snow on Monday, on Thursday we found windslab development on north and east aspects above 6,500'. We have another cold week in front of us and I would continue to watch the new snow at upper elevations for changes in density and slab development as a cold front will typically form wind slabs on south and westerly aspects; which, is generally the opposite side of the mountain from where you will typically find it. For a quick video summary of Mondays obs' click here⇒ https://youtu.be/1B8BceER00A

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
450 AM MST Fri Feb 8 2019

DISCUSSION: A low pressure system will dig down along the Pacific
coast today through Saturday. This low will draw arctic air over
the Continental Divide causing another round of extended gusty
easterly winds and bitter cold. Backcountry travel conditions will
be very dangerous with wind chill colder than minus 40 degrees.
Widespread snow is expected through Saturday, however amounts 
will be lower than the storm that occurred last weekend. The 
heaviest snow will be across northwest Montana, especially around 
Glacier National Park.

Very cold temperatures and occasional light accumulations are
probable for much of next week.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           90%          90%          85%      
Hi/Lo Temps           11 to 17     -13 to -7    -5 to 2  
Winds(mph)            E 11G28      E 22G45      NE 28G55 
Precip Chc            90           100          60       
Precip Type           snow         snow         snow     
Liquid Amt            0.16         0.12         0.06     
Snow Ratio(SLR)       20:1         20:1         20:1     
Snow Amt(in)          3-5          2-5          1-2      
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.