THIS AVALANCHE ADVISORY EXPIRED ON March 13, 2019 @ 4:51 am
Avalanche Advisory published on March 12, 2019 @ 4:51 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Tuesday will bring more snow and southwest winds. Expect windslabs to continue being the main concern on North and East aspects in steep alpine terrain. The new snow may form thin storm slabs as well that will take a couple of days to bond. Use caution in steep terrain and loading zones where even small slabs may take you for a ride.

How to read the advisory

Tuesday will bring more snow and southwest winds. Expect windslabs to continue being the main concern on North and East aspects in steep alpine terrain. The new snow may form thin storm slabs as well that will take a couple of days to bond. Use caution in steep terrain and loading zones where even small slabs may take you for a ride.

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: Wind Slab
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This problem should be easy to spot and easy to manage. Winds were squirrely today but ultimately the southwest flow was winning the battle. Most loose snow on SW aspects was being transported on to the NE side of ridgelines today and the forecast is calling for more of the same. These slabs will likely be fairly thin; but, that doesn't make them harmless.  A thin slab in steep terrain can still take you for a punishing ride. Pay attention to what is below you and avoid steep convexities and steep slopes just below ridgelines as seen in the photo below.



Steep slopes just below these wind-lips will be likely trigger spots through Wednesday.

Avalanche Problem 2: Storm Slab
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Up to 12" of new snow is predicted to fall on the mountains Tuesday through Tuesday night. This new snow will likely fall on the warm side and create a fairly dense and cohesive layer that may take a couple of days to bond to the existing snowpack. Steep terrain over 35° and convex rolls will continue to be areas to keep an eye on.  Pay attention to the upper layer of snow and how it reacts under foot or machine before committing to steep and consequential terrain. New snow will likely bond poorly on south and west aspects were the old snow was scoured by wind or exposed to the sun.

advisory discussion

Todays observations in the Purcell Range continued to verify the good general stability of our snowpack. None of the layers are showing a likelihood of propagating into a slab avalanche at this time. In both the Cabinets and the Purcells there are weak layers about 2' down that we are monitoring. Unlikely to cause a problem but they may come to life if we begin to see really warm days or a rain on snow event in the mountains(something we have mostly avoided this winter!) Aside from that my primary concern is the windslabs on leeward aspects, keep this issue at the forefront of your mind, especially in the higher alpine terrain.

At this point the storm snow is the wild card; the forecast is calling for a decent shot of snow starting Tuesday, how it bonds to the existing snow is something riders will have to assess as they travel. Start with small test slopes to assess the strength of the new snow before going big. By Wednesday afternoon we may start to see afternoon sun again as high pressure returns to the area. Expect any loose surface snow to become readily available for loose wet slides as the March sun peaks out and heats up the snow on South and Westerly aspects.

 

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
500 AM MDT Tue Mar 12 2019

DISCUSSION: A weather system will move through the northern
Rockies today resulting in accumulating snows, primarily late this
morning through this evening. Expect some gusty westerly winds
today, primarily along the continental divide. Expect snow to
become more showery later this evening into Wednesday. 

High pressure will establish itself over the region through early
next week. Expect a gradual warm up each day. 



Kootenai:

--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Wed      
Cloud Cover           95%          85%          70%      
Hi/Lo Temps           27 to 36     20 to 25     27 to 36 
Winds(mph)            SW 14G29     SW 10G23     W  7G20  
Precip Chc            90           80           50       
Precip Type           snow         snow         snow     
Liquid Amt            0.36         0.17         0.04     
Snow Ratio(SLR)       14:1         16:1         18:1     
Snow Amt(in)          4-7          3-4          1        

Snow Level            2500         1500         1500  
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.