THIS SNOWPACK SUMMARY EXPIRED ON December 21, 2017 @ 6:18 amSnowpack Summary published on December 19, 2017 @ 6:18 am
Issued by Ben Bernall - Kootenai National Forest
Heavy snowfall and high predicted winds that are forecasted for the Kootenai have created HIGH avalanche danger. Slab avalanche conditions are developing that may take extensive time to strengthen. These slabs are overlying a layer of buried surface hoar and facets (weak, sugary snow). Avoidance of steep terrain (over 30°) on all aspects above 5,000' is strongly advised!
Avalanche Character 1: Storm Slab
Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.
Abundant snowfall has been blanketing the mountains of the Kootenai N.F. Heavy snowfall is expected to continue to fall in the mountains through Tuesday. This heavy layer of moist snowfall is overlying a multitude of weak layers in the snowpack which will create very dangerous slab avalanche conditions above 5,000' on all aspects. Watch for bullseye data of instability such as extensive cracking and settling.
Avalanche Character 2: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.
The backcountry weather forecast for the Kootenai Region is calling for high winds out of the south and east on Tuesday then transitioning to a Northeasterly pattern as the cold front enters the region on Wednesday. These winds combined with abundant loose snow will likely create dangerous windslabs on most aspects. Avoid steep slopes and cross-loaded terrain features such as gullies and pay attention signs of wind loading such as pillow like formations and density changes within the snow surface.
On December 18th we travelled into the Eastern Cabinets, we were only able to access a southerly and westerly aspect for stability testing but found some interesting layers that were not observed in our trip to the Western Cabinets the week prior. These aspects that were exposed to solar radiation were showing failures on weak facet layers below two seperate sun crusts. The slab layer above these weak layers was over 12" thick and growing. We also heard at least 3 audible collapses as we skinned up the hill. We were unable to find any buried surface hoar on these aspects. Stability tests and observations vary greatly right now as to what weaknesses a rider will find in the snowpack; however, the one consistency we do have is that there are a multitude of weaknesses that can be found on any aspect and they are now being covered by a layer of dense snow that will be ideal for dangerous slab formation.
On December 14th we travelled into the Keeler Rattle area where we found some very impressive surface hoar development. Snowpit stability tests revealed a stout rain crust at the bottom 2' of the snowpack, overlying this was a thin layer of facets covered by another layer of light powder. We observed surface hoar as high as 6,000' in elevation on all aspects although it was much smaller and broken down in areas with a little exposure to wind and sun. In some areas the crystals were up to 1.5" long. Between the facet layer and this widespread surface hoar we will have alot of potential instabilities in the snowpack when snowy weather returns.
Weather and CURRENT CONDITIONS
Backcountry Forecast from NWS Missoula issued: 350 AM MST Tue Dec 19 2017 DISCUSSION: Heavy snow is expected in the mountains and valley locations across Lincoln and Flathead Counties through tonight. Strong southwesterly winds gusting over 45 mph are expected in the higher elevations today and tonight ahead of the Pacific cold front that will move through the region before daybreak Wednesday. Snow levels outside of northwest Montana will generally range between 4000 and 5000 feet then crashing to 2000 feet by Wednesday morning. Expect scattered snow showers and colder conditions Wednesday. Widespread low temperatures in the single digits and teens are expected Thursday morning. Light to moderate snow and gusty north to east winds will accompany an arctic cold front passage Friday. Kootenai: --------------------------- 5000-7000 FT ---------------------------- Today Tonight Wed Cloud Cover 100% 90% 85% Hi/Lo Temps 24 to 32 14 to 21 18 to 25 Winds(mph) SE 13G39 S 21G41 NE 15G32 Precip Chc 100 100 70 Precip Type snow snow snow Liquid Amt 0.97 0.66 0.05 Snow Ratio(SLR) 16:1 17:1 19:1 Snow Amt(in) 13-19 9-11 1-2 Snow Level 2000 2000 500
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.
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