THIS AVALANCHE ADVISORY EXPIRED ON January 1, 2020 @ 5:33 amAvalanche Advisory published on December 31, 2019 @ 5:33 am
Issued by
Ben Bernall - Kootenai National Forest
Kootenai

bottom line
Our current snowpack conditions are very stable but that will begin to change by Tuesday night. A winter storm will bring 1-2 feet of fresh snow and strong winds out of the southwest which will cause avalanche hazards to rise by Wednesday. Be on the watch for fresh storm slabs and wind slabs at tree-line and above throughout the week!
Kootenai
How to read the advisory
Our current snowpack conditions are very stable but that will begin to change by Tuesday night. A winter storm will bring 1-2 feet of fresh snow and strong winds out of the southwest which will cause avalanche hazards to rise by Wednesday. Be on the watch for fresh storm slabs and wind slabs at tree-line and above throughout the week!

1. Low
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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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.
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Persistent Slab
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Likelihood ?CertainVery LikelyLikelyPossibleUnlikely
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The weak layer at the base of our snowpack continues to show gains in strength and is unlikely to create a human triggered avalanche at this time. This problem has some potential in terrain above 6,000' and potential trigger points will be steep and rocky terrain with a thin snowpack.
Avalanche Problem 2: Wind Slab
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We have been observing lots of wind and evidence of slab development in the higher terrain of the West and East Cabinets the last two weeks. Yesterday we found that they are unlikely to react and fairly small in size. This will begin to change by Wednesday as another storm with strong southwest winds enters the area. Expect windslabs to become a problem by Wednesday on north and east aspects at treeline and above.
advisory discussion
On December 30th I toured into the East Cabinets with the goal of assessing the wind slabs at upper elevations and to check on the strength of the weak crust/facet combo at the base of our snowpack. The deep weak layer we have been looking at since the begining of the season is continuing to improve and become more difficult to trigger. We observed lots of older evidence of avalanches on this weak layer that occurred during the warm and rainy weather that rolled in on December 20th. Much of the steep terrain below 6,500' had slid on this weak layer leaving behind large piles of debris and setting the snowpack back to almost nothing in these locations. Stability tests above 6,500' are showing very little reactivity on this layer but every so often it rears it's ugly head to show some potential, at this point the most likely trigger will be another rain on snow event. Outside of this scenario it is unlikely to fail. At upper elevations we spent alot of time checking out the wind slabs on all aspects and found very little to be concerned about, overall conditions were very stable on all aspects and elevations. BUT. My wife called me the "King of Caveats" the other day. As an avalanche guy I consider caveats an integral part of my life. Things will change, as they always do.
The weather forecast is calling for multiple shots of snow throughout the week with strong southerly winds that are likely to cause a spike in avalanche hazard. The snow looks to be coming in with lighter snow densities on Tuesday then transitioning to heavier snow on Wednesday night. This will cause an upside down scenario in the upper snowpack and create a stormslab issue that will be with us throughout the week. Much of the current snow surface has a crust layer and we were seeing a fresh growth of surface hoar below treeline, these conditions are poor surfaces for the new snow to bond to. And, as mentioned earlier, more wind to add to the problem.
So, don't let the LOW hazard rating on Tuesday cause you to drop your gaurd. Bring your A-Game to the mountains and be ready for changes, because you can always rely on changes!
Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued: 340 AM MST Tue Dec 31 2019 DISCUSSION: An atmospheric river will bring heavy snowfall across mountain locations Tuesday into Wednesday. The heaviest accumulations will impact the Clearwater, Bitterroot, Swan, and Mission mountains where several feet of snow is expected. Snow densities initially will be on the low side, with ratios of 15-20:1 this morning, before increasing this afternoon into Wednesday morning with warmer air and strong winds up to 40 mph. A few snow showers could produce graupel Wednesday afternoon as the atmosphere becomes unstable and convective. Flow will turn out of the northwest Wednesday night into Thursday. Widespread snow shower activity is expected for the Bitteroot, Clearwater, and Mission mountains, along with higher snow ratios (~20:1). Kootenai: --------------------------- 5000-7000 FT ---------------------------- Today Tonight Wed Cloud Cover 90% 95% 90% Hi/Lo Temps 27 to 33 24 to 30 29 to 35 Winds(mph) SW 20G48 SW 29G57 SW 24G53 Precip Chc 100 100 80 Precip Type snow snow snow Liquid Amt 0.38 0.72 0.22 Snow Ratio(SLR) 16:1 11:1 15:1 Snow Amt(in) 5-12 6-15 2-8 Snow Level 2000 3000 3500
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.
This website is owned and maintained by the Friends of the Idaho Panhandle Avalanche Center. Some of the content is updated by the USDA avalanche forecasters including the forecasts and some observational data. The USDA is not responsible for any advertising, fund-raising events/information, or sponsorship information, or other content not related to the forecasts and the data pertaining to the forecasts.