THIS SNOWPACK SUMMARY EXPIRED ON March 25, 2016 @ 11:00 pmSnowpack Summary published on March 25, 2016 @ 6:00 am
Issued by Ben Bernall - Kootenai National Forest
Avalanche Character 1: 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.
Mountain locations across the Kootenai N.F. have recieved 8-10 inches of fresh snow above 5,000 feet. This snow sits on top of a melt-freeze crust from March 20th. As elevations increase so does the depth of the freshly fallen snow. Above 6,000 feet and near ridgeline locations this snow was hammered by high winds yesterday (3/24). These winds are expected to continue into the evening and are forecasted to gust up to 35 mph. This new snow is quickly turning into a cohesive and reactive slab at locations that are exposed to high winds.
BOTTOM LINE: Use caution on slopes above 6,000 feet that show signs of being affected by high winds through the upcoming week. Watch for shooting cracks and a "pillowy" like appearance of surface snow. At elevations below 6,000 feet or where the snow is sufficiently sheltered from the wind the new snow is less likely to have formed a cohesive slab and will provide a safer alternative for riding and sliding.
This will be the last Snowpack Summary issued by the Kootenai N.F. for the 2015/2016 winter. Looking beyond the coming weekend (3/27) backcountry travelers should be alert to the general hazards that can be expected while skiing or snowmobiling in spring conditions. Some of the most stable snowpack is often found this time of year but it is also subject to change quickly with sun and warm temperatures. Be especially cautious on slopes with overhead hazards such as cornices and glide cracks, these hazards are unpredictable and it is best to avoid them when possible.
Big thanks to Nate Stephens, Ben Valentine, Linda Hubbel and Alan Osborne for the help this winter and a huge thanks to the Flathead Avalanche Center and all its supporters for providing this platform and improving the safety for winter recreationists.
Today, (3/24) we traveled to Chicago Peak near the southern boundary of the Cabinet Mt. Wilderness. We parked the snowmobiles at an elevation of 5,700 feet where we began breaking trail in 8 inches of fresh snow overlying a supportive crust from the previous weekends warm temperatures. We did our first stability test at 6,700 feet on a south east aspect where we found generally stable conditions that where not highly reactive to tests or ski cutting. There are however mulitple layers within the snowpack that could become a problem with a more significant trigger such as cornice fall or intense sun. As we traveled to the north aspect at the same elevation we moved into terrain that was receiving more wind as well as harboring some weaker snow on the colder side of the mountain. The day's high winds showed some obvious warning signs as we changed aspect-see image below.
Wind slab releasing in skin track on north aspect at 6,700 feet.
The other notable weakness on the north aspects is the persistance of two layers of graupel that have been found within the snow pack as one starts to push above 6,500 feet. A ski partner of mine also noted this weakness near Twin Peak just below 7,000 feet on 3/19. This graupel layer failed with light force in stability tests below a crust layer, producing a 17 inch thick slab. There is a second graupel layer 45 inches below the surface that wasn't reactive to stability tests. However, it is entirely possible that the right force or release of a thinner wind slab could cause a step-down to this deeper layer.
Weather and CURRENT CONDITIONS
Backcountry Forecast from NWS Missoula issued:
Backcountry Forecast from NWS Missoula issued:
230 PM MDT Thu Mar 24 2016
DISCUSSION: Periods of mountain snow are expected today, becoming
showery late today into tonight. In addition, winds will increase,
with gusts topping 50+ mph at elevations of around 6000 feet and
higher by this afternoon. Winds will diminish by Friday morning,
while periods of snow showers will continue in high terrain
through Friday evening. High pressure will lead to warmer and
generally dry conditions much of the weekend.
--------------------------- 5000-7000 FT ----------------------------
Tonight FRI FRI Night SAT
Cloud Cover 95% 95% 50% 50%
Hi/Lo Temps 22 to 28 30 to 41 22 to 27 34 to 40
Winds(mph) W 16G35 NW 7 W 6 SW 8
Precip Chc 60 80 0 0
Precip Type sno/shr sno/shr sno/shr none
Liquid Amt 0.08 0.13 0.00 0.00
Snow Ratio(SLR) 14:1 15:1 14:1 0
Snow Amt(in) 1-2 1-2 0 0
Snow Level 3000 2500 3000 3000
This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.
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