THIS AVALANCHE ADVISORY EXPIRED ON February 22, 2020 @ 4:56 am
Avalanche Advisory published on February 21, 2020 @ 4:56 am
Issued by Melissa Hendrickson - Idaho Panhandle Avalanche Center

Kootenai

bottom line

Wind slabs from earlier in the week have become stable and resistant to triggering. There are some persistent weak layers in the upper snowpack but are showing a low likelihood of propagating into an avalanche. Use extra caution in the mountains of the Purcell Range (NW Peaks area). Elevations above 6,500' in the Purcells will have the highest potential for human triggered avalanches at this time. Read on for details!!

How to read the advisory

Wind slabs from earlier in the week have become stable and resistant to triggering. There are some persistent weak layers in the upper snowpack but are showing a low likelihood of propagating into an avalanche. Use extra caution in the mountains of the Purcell Range (NW Peaks area). Elevations above 6,500' in the Purcells will have the highest potential for human triggered avalanches at this time. Read on for details!!

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

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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    Very Likely
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    Unlikely
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The snowpack is well settled and generally stable at this time. The weakest spots out there are in the Purcell Range where the cold temperatures have created two layers of facets (weak, sugary snow). The deepest layer is under the February 1st rain crust, approximately 18-20" below the surface. This lower layer is resistant to propagating and showing a trend towards increasing strength. As you climb higher in elevation the crust layer will become thinner and has a higher chance of giving you trouble.The upper layer of facets rests underneath a very soft slab that is 8-10 inches thick. This upper layer may slough easily and in some locations may release in the form of small, soft slabs where the wind has compressed it. Outside of the Purcell Range the Cabinets are showing a much more cohesive and predictable snowpack.

Avalanche Problem 2: Wind Slab
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Fresh snow last weekend and abundant winds out of the west created slabs on leeward terrain last weekend that were concerning on Monday. Observations yesterday showed that these slabs and drifts have gained tremendous strength and will be resistant to human triggers. If you can avoid these slabs it is always a good idea for the sake of habit and I would definetly be careful near any large cornices as they are weak and breaking easily.

advisory discussion

On Monday we travelled into Northwest Peaks Scenic Area. We had a couple of weak faceted layers in pit tests that were somewhat concerning but showing a resistance to propagating into an avalanche and causing a rider harm. I think right now the highest potential is at the very highest terrain in the Purcells. Highmarking above Hawkins Lakes or in the steeper terrain of that area may be the way to get into trouble at this time. The wind slabs that were my main concern on Monday were pretty stiff and strong yesterday. Lots of stomping on test slopes gave some pretty promising results across all elevation bands. As mentioned, the cornices are getting pretty big in some locations and it is worth giving them a wide berth if you can't see the edge. 

Looking into the future and potential problems I am seeing facets developing under the crust layers in locations where the wind has scoured all the recent snow away. Warm days and cold nights will continue to build this weakness. I was also seeing some small surface hoar starting to grow in the Purcells, whether or not it survives the sun and wind is yet to be determined. The next possible snow looks to be arriving on Sunday night. At this point accumulations look pretty light so these near surface facets and surface hoar may not become a problem. Stay tuned and enjoy the sun!!

Weather and CURRENT CONDITIONS
weather summary 
DISCUSSION: 

Northwest Montana: The high pressure ridge over the Northern
Rockies flattens out today and transitions to westerly flow ahead
of the next system. Clear skies and mild temperatures persist. 
High clouds begin to filter into the area from the northwest 
tonight as Pacific moisture begins to make its way westward. 
Clouds will build throughout the day on Saturday. The next chance 
for precipitation is still on track for Sunday night into Monday.

West Central Montana: The high pressure ridge over the Northern
Rockies flattens out today and transitions to westerly flow ahead
of the next system. Clear skies and mild temperatures persist. 
High clouds begin to filter into the area from the northwest 
tonight as Pacific moisture begins to make its way westward. The
Bitterroots could see some high clouds tonight. Clouds will build
throughout the day on Saturday. The next chance for precipitation
is still on track for Sunday night into Monday.

Central Idaho: The high pressure ridge over the Northern
Rockies flattens out today and transitions to westerly flow ahead
of the next system. Clear skies and mild temperatures persist. 
High clouds begin to filter into the area from the northwest 
tonight as Pacific moisture begins to make its way westward. 
Clouds will build throughout the day on Saturday. The next chance 
for precipitation is still on track for Sunday night into Monday.


Kootenai:

--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           15%          40%          35%      
Hi/Lo Temps           27 to 35     16 to 21     30 to 37 
Winds(mph)            SW 13G23     SW 10G22     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            2000         2500         2500
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.