THIS AVALANCHE ADVISORY EXPIRED ON January 9, 2019 @ 4:58 am
Avalanche Advisory published on January 8, 2019 @ 4:58 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Sunday nights storm dropped 12-18" of snow on the Cabinet Mountains. This new snow formed sensitive storm slabs that will be reactive in steep terrain, give the new snow time to settle and strengthen before venturing into steep terrain this week. In the Purcells the "persistent slab" problem continues to lurk, it is a low-likelihood/high consequence scenario. Practice safe travel habits and use caution in likely "trigger spots" such as steep, convex rolls and areas where the snowpack is thin.

How to read the advisory

Sunday nights storm dropped 12-18" of snow on the Cabinet Mountains. This new snow formed sensitive storm slabs that will be reactive in steep terrain, give the new snow time to settle and strengthen before venturing into steep terrain this week. In the Purcells the "persistent slab" problem continues to lurk, it is a low-likelihood/high consequence scenario. Practice safe travel habits and use caution in likely "trigger spots" such as steep, convex rolls and areas where the snowpack is thin.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Storm Slab
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A quick look at area snotel sites will reveal that the Cabinets got walloped by snowfall yesterday and the Purcells came away with a scant dusting of new snow. With well over a foot of new snow expect to find touchy storm slabs on all aspects in the Cabinet Ranges. The reactivity of this storm slab will be dependent on the surface that it is resting on; which, is highly variable across the area. Use caution in the Cabinets this week on all steep terrain (over 30°) until this new snow has settled.

Avalanche Problem 2: Persistent Slab
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The Purcell Range is still harboring the deep and stubborn weaknesses that have been "persisting" since winter began. As I mentioned in the "Bottom Line", this is a low-likelihood/high consequence scenario. These weaknesses are healing slowly and will be difficult to trigger; but, if you do there is potential for these layers to go deep and big. This issue also gets us into "Deep Slab" problems and I am lumping "Deep slabs" into this for the sake of brevity and the fact that a slide could step down to the weak, sugary snow at the base of the snow pack. This kind of problem can be difficult to deal with and hard to predict. Be especially alert any time we have a quick change in loading or temperature. Make a habit of carrying the right gear and practicing safe travel habits in avalanche terrain. 

advisory discussion

The Kootenai is a very large area to forecast for with three distinct ranges and personalities. With two field days per week spread across this area it is sometimes hard to forecast with a high degree of certainty and quantify the hazards in all three ranges. Having said that, here is what we are seeing out there.

East and West Cabinets: the "persistent slab" problem has not been much of a concern in these ranges. The avalanche problems have been primarily a result of wet and windy storms rolling in out of the southwest and leaving us with wind slab and storm slab issues. This is fairly easy to deal with, time and terrain is the answer. Give the new snow time to settle this week and find some lower angle terrain or ridgelines to play on until things settle out. 

Purcell Range: The snowpack is generally a little thinner and the air is a little cooler in the Yaak. This has left us with a few weak layers that we have kept an eye on all season and will continue to watch. Yesterday in the Spread Creek area we found buried surface hoar about 16" below the surface, a layer of rounding facets buried about 3 feet deep and weak sugary snow at the base. None of these problems showed a likelihood to progagate in stability tests; but, they have not fully healed. They are most likely to react when they take on additional heavy loads of snow, rain or drastic rise in temperature. Below is a link to a recent fatality that happened near Choteau, MT.  A sad reminder of how dangerous "persistent slabs" can be.

https://www.flatheadavalanche.org/observation/site-investigation-south-w...

 

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
340 AM MST Tue Jan 8 2019

DISCUSSION: A ridge of high pressure has moved over the Northern
Rockies giving way to diminished showers and decreased cloud
cover. This ridge will be short lived as a warm front will move
into the north central Idaho this afternoon and into western
Montana over night. This front will cause increased precipitation
with rising snow levels and decrease snow ratios. 

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Wed      
Cloud Cover           70%          95%          90%      
Hi/Lo Temps           22 to 27     18 to 24     29 to 35 
Winds(mph)            SE  8G22     E 10G23      SE 13G32 
Precip Chc            0            80           90       
Precip Type           snow         snow         snow     
Liquid Amt            0.00         0.13         0.19     
Snow Ratio(SLR)       18:1         13:1         10:1     
Snow Amt(in)          0            1-3          2-3      

Snow Level            500          1500         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.