Likelihood ?CertainVery LikelyLikelyPossible
Size ?HistoricVery LargeLarge
There is a possibility to find pockets of wind slab out there on the highest peaks above 7,500' on leeward apsects. This would be the tops of the very highest mountains in the East Cabinets. If you find yourself up there, you likely know the game you play! Be alert to this potential in steep terrain on north and east aspects above the rain-line!
On February 3rd we scratched our way into the East Cabinets to see just how high and stout the rain crust had formed. The crust transitioned from "bullet-proof" to somewhat breakable around 5,000'. The crust at upper elevations is about 1" thick and very icy. At upper elevations we observed long cracks in the snowpack surface on steep terrain and ridgelines. It appeared that gravity was taking its' toll on the snowpack. I am guessing that another day of rain and warm temperatures this past weekend would have resulted in a pretty massive natural cycle.
We observed these long cracks in the surface on all aspects and they were also common on ridgelines with cornices. We ran out of mountain at about 7,000' and the crust layer was still very firm. Best guess at the rain line looked to be at about 7,500'. With strong winds and precipitation last weekend I think it is pretty likely you will find some stiff and stubborn pockets of wind-slab above this line. This is a very small portion of the terrain in the area that would be a concern for the highest peaks in the East Cabinets. Otherwise, avalanches may be the least of your concern, falling down and taking a long slide on an icy crust is much higher on my concern list right now!
This new ice crust is a bench-mark layer that will be on the radar of things to watch in our snowpack for sometime this winter. It really hits the reset button and locks the snow-pack together; but, it will also make a poor surface for bonding as new snow falls. In the near future it looks like snow will start to fall light and cold Tuesday night then slowly warm up and fall a little on the dense side by Wednesday afternoon. This may set us up for some slab development on Wednesday and Thursday. If you are going out mid-week, be alert for the potential of thin storm slabs to develop and slide easily in steep terrain.
Backcountry Forecast from NWS Missoula issued: 500 AM MST Tue Feb 4 2020 DISCUSSION: Northwest Montana: A clear start to today will give way to the beginnings of a long period of unsettled weather. Satellite imagery is currently showing a nice plume of Pacific moisture streaming over the Pacific Northwest. This will arrive in the Northern Rockies tonight via strong northwest flow. Snow continues into the weekend. Warm frontal passage Wednesday night will bring snow levels up to 4000 feet and increase snow density in higher elevations. Winds today will be moderate, primarily west and southwest. You will experience higher wind speeds east of the Continental Divide.
Kootenai: --------------------------- 5000-7000 FT ---------------------------- Today Tonight Wed Cloud Cover 35% 85% 95% Hi/Lo Temps 16 to 23 12 to 18 24 to 30 Winds(mph) SW 13G29 SW 20G36 SW 17G32 Precip Chc 0 60 70 Precip Type snow snow snow Liquid Amt 0.00 0.09 0.18 Snow Ratio(SLR) 22:1 21:1 19:1 Snow Amt(in) 0 1-5 3-8 Snow Level 0 0 500
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.
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.