THIS AVALANCHE ADVISORY EXPIRED ON January 24, 2019 @ 9:18 am
Avalanche Advisory published on January 23, 2019 @ 9:18 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai
Selkirks/Cabinets
St. Regis Basin/Silver Valley

bottom line

Substantial snowfall, strong winds and some very reactive weak layers are creating HIGH AVALANCHE DANGER at treeline and below. Avoid travelling on or below all terrain that is steeper than 30°. 

How to read the advisory

Kootenai
Selkirks/Cabinets
St. Regis Basin/Silver Valley

How to read the advisory

Substantial snowfall, strong winds and some very reactive weak layers are creating HIGH AVALANCHE DANGER at treeline and below. Avoid travelling on or below all terrain that is steeper than 30°. 

3. Considerable

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

4. High

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Near Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Below Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Storm Slab
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Building storm slabs are resting on very weak surface hoar crystals, crust layers and facets. The most reactive slopes will be at elevations below 5,500' where surface hoar crystals are growing on top of a firm crust. Expect slopes in valley bottoms that you normally wouldn't recognize as avalanche terrain to become sensitive to human triggers and avoid all avalanche terrain. These slabs will vary in thickness across the area but it is likely that we may see a cycle of natural avalanches through Thursday. 



Surface hoar crystals such as these are being buried on all aspects below 6,500' in areas that were sheltered from wind and sun. These large, feathery crystals will form a lubricating layer that is difficult for new snow to bond to.  At elevations above 6,500' the new snow will be falling on a sun crust on southerly aspects that will also provide an easy surface for snow to slide off of.

Avalanche Problem 2: Wind Slab
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On Tuesday there was substantial winds swirling in the Cabinets at a steady 20 mph that shifted in mulitiple directions. I recieved observations from local skiers that were able to intentionally trigger some small, "pillowy" pockets in wind loaded terrain. With fresh snow available for transport over night it is likely that these wind slabs became thicker and more cohesive through the evening at treeline and above.

Avalanche Problem 3: Persistent Slab
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There are some deeply buried facets and depth hoar layers across the area that have been sleeping and showing very little reactivity in stability tests. Additional weight from the recent storm snow may be what tips the scales for this weakness in areas where the snow pack is thin and lacking in strength. Triggering a storm slab in steep terrain may also cause a "step-down" to these deeper weak layers resulting in deeper burials.

advisory discussion

I will keep this short and sweet! We have a very widespread and substantial weak layer of surface hoar below 6,500'.  Below 5,500' it is resting on a crust layer that is also developing facets below it. With the storm snow and wind that entered the area Tuesday night we are adding the final ingredient neccessary for a significant avalanche cycle. I would suggest avoiding all avalanche terrain (steeper than 30°) in the coming days and remember that HIGH DANGER means human triggered avalanches are VERY LIKELY! Go play in low angle terrain or find something safer to do than roll the dice in the mountains this week.

recent observations

Big thanks to all the folks who contacted me and the other forecasters with observations last night and today. Much appreciated!

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
340 AM MST Wed Jan 23 2019
DISCUSSION: The current winter storm is on track and looking good so
far. The track and timing hasn't changed much from previous model
runs...lending to high forecaster confidence. A foot of new snow 
is still expected by later this evening, with lighter snow 
showers persisting above 5000 feet thereafter. The period of 
heaviest snowfall with the highest snow ratios will occur this 
morning, lasting through roughly Noon MST or so before snow 
starts to diminish from north to south with time. 

For WC MT and NC ID: Snow levels in the southern Bitterroots and 
into the Hwy 12 corridor may still fluctuate this afternoon. The 
good news is: the latest forecast models show this fluctuation to
be much less pronounced than before in these areas. As a result,
the chance for rain at midslopes seems much less likely. SWE will
range from 0.60" to 0.95".

--Allegretto


Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Thu      
Cloud Cover           80%          55%          65%      
Hi/Lo Temps           27 to 32     17 to 22     26 to 30 
Winds(mph)            N  9G22      W  7G20      SW 12G25 
Precip Chc            90           0            20       
Precip Type           snow         none         snow     
Liquid Amt            0.27         0.00         0.01     
Snow Ratio(SLR)       17:1         0            16:1     
Snow Amt(in)          3-7          0            0-1      
Snow Level            1500         1500         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.