THIS AVALANCHE ADVISORY EXPIRED ON January 30, 2019 @ 5:45 am
Avalanche Advisory published on January 29, 2019 @ 5:45 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

The buried surface hoar can still be found below 6,500' in elevation. It has become less reactive in most locations but it is still possible to trigger a slide on this weak layer. Use caution in steep and sheltered drainage locations where you could trigger a small slide on surface hoar under last Wednesdays' storm snow.

How to read the advisory

The buried surface hoar can still be found below 6,500' in elevation. It has become less reactive in most locations but it is still possible to trigger a slide on this weak layer. Use caution in steep and sheltered drainage locations where you could trigger a small slide on surface hoar under last Wednesdays' storm snow.

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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There are currently two surface hoar layers within the snowpack. The older and larger layer of crystals that developed mid January is becoming less reactive in stability tests and showing a low likelihood of failure and propagation. A small layer is being found underneath last Wednesdays storm snow in isolated drainage bottoms below 6,000' that was reactive and producing shooting cracks and collapsing. It seems to be very much contained to protected pockets and will likely produce soft slab avalanches 10" thick. Use caution near creek/drainage bottoms in the mountains at elevation between 4,000-6,000' where these sensitive pockets may exist.



Shooting cracks and 10" soft slabs reacting January 28th in isolated and protected draws where surface hoar developed between storms.

Avalanche Problem 2: Wind Slab
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This past weekend the mountains of the Kootenai saw multiple days of sun, and fairly warm temperatures were recorded at snotel sites on the 26th and 27th. This largely removed the opportunity for the wind to transport much snow for loading. On Sunday the area received fairly strong winds out of the north that created some thin and reactive wind slabs on northerly aspects. Yesterday we observed them to be 2-3" thick, pencil hard and easy to release. They are generally small enough to be harmless to riders but worth paying attention to as they may be thicker in isolated pockets at upper elevations. It is likely that this thin skin of firm snow will be our next weak layer when more snow falls.

advisory discussion

On January 28th we travelled into the East Cabinets with the goal of checking out the stability and reactivity of the buried surface hoar layer. Extended column tests at mid and lower elevations revealed that the surface hoar was buried under about 15" of cohesive slab but was not showing to be highly reactive or propagating in these tests. As we dropped into the drainage bottom we were able to trigger small soft slabs on buried surface hoar in convex terrain at 5,500' in a north facing drainage.  This layer was also producing some large shooting cracks and audible collapsing. We covered alot of fairly steep terrain yesterday from 3,500' up to 7,600' on multiple aspects and these protected draws were the only location where we found signs of instability. Steep, and protected(i.e. sheltered from wind and sun) draws are the places you will want to be wary of the next few days. The other interesting observations were the obvious evidence of warm mountain temperatures and strong northerly winds. With warm air and sun present on this past Friday and Saturday there wasn't much loose snow available for transport. When the strong northerly winds came out of the north on Sunday it produced a thin, stiff skin on open and exposed terrain at upper elevation. This skin broke loose easily with weak snow below it and we observed multiple locations where it realeased on its own accord in steep terrain. It's a pretty harmless slab; but, there may be thicker pockets in extreme terrain and I mention it for that reason. It will also make a poor surface for bonding when the next storm rolls in. On southerly terrain the snow surface is also pretty stiff right now due to the warm sunny days and cool nights. The stability however on these solar aspects is pretty good, we observed some older rollers but nothing was moving yesterday and the surface is firm enough now that loose wet slides will be small and infrequent the next couple of days. Link to short video of yesterdays obs! https://youtu.be/-TSFVQyCSn4

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
550 AM MST Tue Jan 29 2019

DISCUSSION: A ridge of high pressure is building over the region
and will dominate the weather until Friday. The system for this
weekend will start out warm and wet and then turn colder. There is
still much uncertainty with how far west of the Continental Divide
the east winds and arctic air will penetrate.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Wed      
Cloud Cover           10%          15%          70%      
Hi/Lo Temps           24 to 29     9 to 14      25 to 30 
Winds(mph)            SE  5        SW  9G22     SW 11G25 
Precip Chc            0            0            0        
Precip Type           none         none         none     
Liquid Amt            0.00         0.00         0.00     
Snow Ratio(SLR)       0            0            0        
Snow Amt(in)          0            0            0        

Snow Level            1000         1000         1000     
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.