THIS AVALANCHE ADVISORY EXPIRED ON December 29, 2018 @ 5:15 am
Avalanche Advisory published on December 28, 2018 @ 5:15 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Generally stable snowpack conditions exist below treeline. Above treeline there are still persistent weak-layers within the snowpack, the Purcell Mountains are where you are most likely to find these weak layers. Human triggered avalanches are not likely; but, will be large and have high consequences if triggered. Moving forward into the weekend there is the potential for stability to decline if the next predicted storm materializes. Continue to practice safe travel habits and keep an eye on the weather.

How to read the advisory

Generally stable snowpack conditions exist below treeline. Above treeline there are still persistent weak-layers within the snowpack, the Purcell Mountains are where you are most likely to find these weak layers. Human triggered avalanches are not likely; but, will be large and have high consequences if triggered. Moving forward into the weekend there is the potential for stability to decline if the next predicted storm materializes. Continue to practice safe travel habits and keep an eye on the weather.

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

?

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

There are still some "persistent weak layers" buried within the snowpack. These layers are still worth paying attention to in steep terrain above 6,500', particularly in the thinner snowpack of the Purcell Range. Use caution and check out the snowpack before committing to steep terrain above tree-line, and as always practice safe travel habits when playing on or near steep terrain. As I mentioned, this problem fits into a low-likelihood/high consequence situation. 

recent observations

On December 27th we travelled back into the Cabinets with the goal of gaining some altitude and thouroughly checking out the potential for any lurking wind slabs at upper elevations on leeward terrain. The tour verifiied that the recent wind slabs have stabilized and are unlikely to cause a problem at this time. We encountered generally stable conditions on all aspects. There are a lot of thin, hollow spots and sugary snow near wind-swept ridgelines and on south-westerly aspects that could present a problem moving forward if the area comes under north-easterly winds. This is always a possible scenario during cold front passages. We dug into the snow on a southerly aspect to check out the snow on the thin side of the mountain where we observed some weakness (old graupel and 2 crust layers). Neither of these layers proved to be reactive or show the potential to propagate at this time. 

Moving forward into the weekend there is potential that snow conditions will change as the National Weather Service is hinting at a storm moving into Western Montana late Saturday and Sunday. Looking at the forecast it seems possible that the brunt of this storm may miss the area. Continue to keep an eye on the forecast this weekend and give steep slopes some time to settle if we recieve another dose of heavy snow in the mountains.

Check out the short video below to see the snowpack in the East Cabinets, 6.5' at this location on Christmas Eve.  Game on!

https://youtu.be/8CAAP7_L62o

 

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
1220 AM MST Thu Dec 27 2018

DISCUSSION: Lingering snow showers over the terrain of west-
central Montana, including the Mission Mountains are expected to 
finally diminish by mid morning. Our next weather system will 
begin to spread light to moderate snow over western Montana late 
tonight and persist through the day tomorrow. No significant 
accumulations are expected with this disturbance. The next 
potential significant weather system is possible by the end of the
weekend. Confidence on snowlevels remain uncertain due to 
disagreements between Models, though moderate to heavy snow for 
the higher terrain is likely.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Tonight      Fri          Fri Night    Sat      
Cloud Cover           35%          75%          90%          95%      
Hi/Lo Temps           7 to 16      17 to 23     14 to 20     27 to 32 
Winds(mph)            NW  8G22     SW  9G23     SW 14G31     SW 18G39 
Precip Chc            0            30           60           80       
Precip Type           snow         snow         snow         snow     
Liquid Amt            0.00         0.01         0.03         0.09     
Snow Ratio(SLR)       19:1         19:1         18:1         14:1     
Snow Amt(in)          0            0            0            1        

Snow Level            0            0            0            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.