THIS AVALANCHE ADVISORY EXPIRED ON December 25, 2019 @ 5:26 am
Avalanche Advisory published on December 24, 2019 @ 5:26 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Avoid steep terrain above 6,000' on north and east aspects. It will still be possible to trigger the recent storm snow in these locations and triggering small windslabs will be likely on high, steep terrain. These winds slabs and storm slabs will decrease in sensitivity during the week as temperatures return to seasonal normals and the winds subside. 

How to read the advisory

Avoid steep terrain above 6,000' on north and east aspects. It will still be possible to trigger the recent storm snow in these locations and triggering small windslabs will be likely on high, steep terrain. These winds slabs and storm slabs will decrease in sensitivity during the week as temperatures return to seasonal normals and the winds subside. 

3. Considerable

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

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.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Strong southwest winds have likely created small but sensitive windslabs on leeward slopes above 6,000'. Use caution near ridgelines on north and east facing terrain above this elevation. Steep chutes and convex roll-overs will be likely places to find trouble in the highest terrain.

Avalanche Problem 2: Storm Slab
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Last weekends storm brought massive amounts of moisture to the high peaks of the Kootenai. At "treeline" elevations it fell as a mix of rain and snow and has begun to stabilize as temperatures lower. Above 6,000' the moisture came in as all snow and is trending towards improved stability; but, it is still likely you will trigger a slide in the top 3-4 feet of the snowpack in steep terrain at upper elevations. 

Avalanche Problem 3: Persistent Slab
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The base of our snowpack is housing some structural weakness consisting of early season ice layers sandwiched by weak sugary snow. These layers are now very deep and will likely be resistant to human triggering. These weak layers will become active as we add stressors such as last weekends warm temps and heavy amounts of moisture. Many avalanches ran on these deep weak layers last weekend as the snowpack took on the stress of added water weight and was weakened by above freezing temperatures.

advisory discussion

Last weekends storm delivered impressive amounts of moisture between Thursday evening and Sunday. Hawkins Lake Snotel recieved 5.3" of snow water equivalent (SWE) and Bear Mountain picked up 6.9" of SWE during this period. The snow line fluctuated up and down the hill during this period leaving us with an interesting scenario where tons of high elevation snow sits on the peaks but very little snow remains down low; thus, making the access for getting there less than awesome. During the storm lots of steep terrain avalanched at the elevation band where the temps were hovering just above the freezing mark. We observed many crowns yesterday that appeared to release on the deep weak layers (crust/facet combos), all the observed crowns were at 6,500' and below. At elevations above 6,500' we observed no recent avalanche activity but there is a thick, dense blanket of snow on north and east aspects due to the strong southwest winds that came in with the storm. The new snow is bonding relatively quickly as the temperatures return to seasonal norms.

During our tour we were also greeted with steady 15mph winds and strong gusts out of the southwest once on the ridgeline. These winds were continuing to build the windslab problem at the upper elevations and I was able to trigger small windslabs on test slopes with an easy ski-cut.

At lower elevations (below 5,000') there is very little snow left. Good news-low avalanche danger. Bad news-lots of brush to thrash through if you want to get to the snow up high.

Weather and CURRENT CONDITIONS
weather summary 
Backcountry Forecast from NWS Missoula issued:
340 AM MST Tue Dec 24 2019

DISCUSSION: Widespread light snow accumulations are expected 
across west central and southwest Montana today with the passage
of a weak low pressure system. Spotty snow showers will also occur in
northwest Montana and north-central Idaho with only minimal
accumulations. Winds will be light today. Wednesday and Thursday 
will be mostly dry across the entire Northern Rockies, aside of a 
few lingering showers on the terrain. Snowfall picks up again on 
Friday in northwest flow but amounts will be light, meanwhile 
westerly winds will increase on the terrain. Seasonable 
temperatures are anticipated throughout the week. 

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Wed      
Cloud Cover           65%          65%          75%      
Hi/Lo Temps           24 to 31     15 to 20     22 to 28 
Winds(mph)            SW  8        SW  9G21     NW  8G20 
Precip Chc            30           0            0        
Precip Type           snow         none         none     
Liquid Amt            0.01         0.00         0.00     
Snow Ratio(SLR)       18:1         0            0        
Snow Amt(in)          0            0            0        

Snow Level            2000         1500         500
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.