National Weather Service Forecast predictions for the coming weekend are calling for an end to the warm sunny days which will be replaced by rain and temperatures running 10-15 degrees F above normal. This weather scenario will likely bring rain to the lower elevations and potenial for new snow above 5,000 feet. At this point it does not look like we will be recieving heavy acumulations. However, this snow will be falling on either a new melt-freeze crust or freshly developed surface hoar (image). Any new snow that falls at higher elevations this weekend will likely form a poor bond with the existing snowpack. This avalanche problem is hard to predict at this point due to the reliance on incoming weather.
Again we are looking at a potential problem that is weather dependent. The past few days have brought in some vary warm temperatures in the mountains of the Kootenai National Forest that have created some small point releases and roller activity. This scenario will likely continue over the next few days with the incoming weather. A rising and falling snow line and warm temps will continue to create some small point release slides. At this point the snowpack is showing a good deal of strength due to the last few days of thawing and refreezing (i.e. crusty) and any releases from rain and warm weather are likely to be small unless we recieve higher than predicted snow accumulations at lower elevations
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Today (February 11th) Nate and I traveled into the Buckhorn Ridge area of the Purcell Mountain Range. After a warm and sunny week with temperatures reaching into the upper 40s we expected some crusty conditions. Our pessimism fulfilled itself as we snowmobiled up to an elevation of 6,000 feet to find a nice supportive crust with a layer of surface hoar forming due to the cool nights above 5,500 feet. This surface hoar development is likely to be pretty scattered across the forest. Temperature inversions have been holding in pockets of cold air in the valley bottoms, and warm air seems to be trapped at the middle elevations below 5,500 feet. Above this level we observed scattered pockets of surface hoar at upper elevations where colder, moist air has been growing some substantial crystals.
Whether or not this surface hoar development creates a long term problem for snowpack stability will be determined by how high the rain climbs this weekend. Warm temps and rain could break it down; however, it could get buried with a fresh layer of snow causing a very weak interface and a tricky avalanche problem in the future.
We dug a snow pit at 6,100' on a northeast aspect where we found terrible skiing conditions but a very stable snowpack. The weakest points in the stability tests failed with hard force at 12 inches (below the January 28th rain crust) and at 19 inches on a snow density change (ECTN24) below the surface. These failures had a fairly clean shear but did not propagate across the column.
Backcountry Forecast from NWS Missoula issued:
320 PM MST Thu Feb 11 2016
DISCUSSION: A change is finally on our doorstep, as the region
transitions to a more active, wetter pattern. To start, showers
will overspread northwest Montana later today through tonight,
while snow levels rise to 6000 feet and higher. A few stray
showers could make it to parts of west central Montana and north
central Idaho, but overall the best focus will remain across
northwest Montana. This will change Friday through Saturday as a
cold front crosses the entire Northern Rockies and precipitation
becomes more widespread with time. Snow levels will then drop to
below 5000 feet by Saturday, changing rain to snow for mid slopes
and high terrain. Some snow may make it to the lowest elevations,
but confidence is not great at this time.
A few notes: this system has sped up from previous model runs, and
depending on how fast or slow snow levels rise today and Friday
will ultimately decide how much snow falls, and where it falls.
This is an inherently difficult forecast, so please stay abreast
to future updates.
--------------------------- 5000-7000 FT ----------------------------
Tonight FRI FRI Night SAT
Cloud Cover 95% 95% 90% 90%
Hi/Lo Temps 32 to 35 38 to 42 26 to 32 31 to 36
Winds(mph) S 5 S 7 SW 12G25 SW 15G29
Precip Chc 80 80 90 80
Precip Type showers showers sno/rain sno/shr
Liquid Amt 0.10 0.21 0.24 0.12
Snow Ratio(SLR) 10:1 11:1 12:1 18:1
Snow Amt(in) 0-1 1 0-2 2-3
Snow Level 5000 5500 6000 3500
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.