Issued: Dec. 11, 2013, 7:00 a.m.
Valid Until: 11:59 p.m. of issue date
Good morning! This is Todd Hannan with the Flathead Avalanche Center avalanche advisory for Wednesday, December 11, 2013. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Saturday, December 14, 2013.
Temperatures began to climb out of the negatives this week and should continue to slowly rise. We have seen varying amounts of precipitation across the advisory area in the past 36 hours ranging from 4” to 20” of snow and 0.2”-1.00” SWE. Currently remote weather stations are reading 10 to 12F with southwest ridge top winds at 10-20 mph. Expect partly to mostly cloudy skies today with isolated light snow showers and southwesterly winds 10-20 mph. After a short lull in precipitation we should see a return to snow late Thursday or early Friday.
We traveled to Noisy Basin yesterday planning to investigate an avalanche that was reported on Sunday (12/08/2013) but were unable to see any sign of it because of new snow covering debris. Based on reports from other locations within the advisory area, the Swan Range was favored for snowfall amounts in the last 36 hours. The Noisy Basin Snotel reported 15” of new snow with .90” swe for the 24 hour period ending at 7:00 last night. During our ascent we remotely triggered cutbanks and small terrain features as we approached. Crown heights ranged from 12-18 inches and failure occurred within a layer of very low density snow deposited at the onset of the storm. Ski patrol at Whitefish Mountain Resort reported 7-10” of low density snow yesterday morning with calm winds. Minimal results were recorded during avalanche control with both ski cutting and explosive use. BNSF avalanche safety team was able to intentionally trigger both a hard slab and a soft slab involving new snow with ski cutting yesterday in John F. Stevens Canyon in Southern Glacier National Park (observation).
Avalanche Problem #1
Recent unsettled storm snow and associated wind will remain a concern today. The Swan range was the big winner for snowfall totals with 15-20 inches yesterday in Noisy Basin. The low density snow will allow for transport without very strong wind and these newly developed wind slabs could be sensitive to human triggering, especially as temperatures continue to rise. The new snow will also disguise previously developed wind slab.
Avalanche Problem #2
The buried surface hoar, crusts, and facets have not been very reactive except in isolated areas, but still exist in our snowpack and are capable of producing an avalanche. Careful evaluation of these layers and how they react to the new load is important on all aspects and elevations.
Overall, the avalanche hazard is CONSIDERABLE. This means that human triggered avalanches are likely particularly on steep slopes with unsettled and wind affected recent storm snow and in areas where buried surface hoar and crust layers are more reactive.
Mark Dundas of BNSF avalanche safety discusses snowpack layering and intentionally triggered avalanches.
Observations are extremely valuable to us. If you’ve been out in the backcountry, please drop us a line with your observations at firstname.lastname@example.org or call 406.261.9873. Thanks!
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 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.