Mostly stable conditions exist with MODERATE avalanche danger in isolated areas above 7000 feet where the snow is shallow and on rocky terrain steeper than 35 degrees. The avalanche danger is LOW on other high elevation terrain. The lower elevation terrain is fairly locked up now thanks to the moderate temperatures and melt-freeze cycles of the past few days.
Good morning backcountry sliders and riders! This is Steve Karkanen with today’s avalanche advisory from the West Central Montana Avalanche Center. This information is the responsibility of the Forest Service and does not apply to operating ski areas. The danger rating expires at midnight tonight.
Weather and Snowpack
This morning SNOTEL stations are reporting temperatures in the twenties and low thirties. Wind speeds this morning are SSE 3 gusting to 11 at Point Six and SSE 16 gusting to 20 mph at Deer Mountain at east of Darby. Hoodoo picked up 4 inches new snow and North Fork Jocko 7 inches in the past 24 hours.
Our moderate weather has given us more confidence that the overall condition of the weak basal layers has vastly improved over the past 2 weeks. Although its unlikely, shaded, shallow snow on steep rocky terrain above 7000 feet are the places where it is possible to trigger a slide to the ground on this persistent weakness.
In the Lost Trail Pass backcountry, Ed Snook, Dave Fox, Geoff Fast and Dudley found this layer to be reactive only after a lot of force is applied to an isolated column and no propagation in extended column tests (see profile below).
They did report finding the surface hoar that formed earlier in the week but there wasn’t enough new snow to make it reactive or to form a slab.
David Williams, Justin Singer and I visited Hoodoo Pass Thursday and did not find the surface hoar. I expect the sun destroyed it in many places Wednesday. What we found at Hoodoo was a nearly isothermic snowpack with a surface condition hard enough to walk around on. The depth hoar that formed in early December is mostly gone in fact the bottom 16 inches is solid (1 finger to pencil hard) and wet. Similar conditions exist around Lolo Pass.
Earlier reports from the Rattlesnake and southern Swan also show continued strengthening of the overall snowpack.
It is easy to move around now but remember, it is early and there are a lot of other hazards like rocks, logs and stumps poking out just waiting to tear your sled up or rip the edges off your skis or board.
Weather and Avalanche Forecast
The Missoula Office of the National Weather Service is forecasting heavy wet snow to begin Saturday with Bitterroot mountain passes expected to receive between 4 and 12 inches before the event transitions from snowfall to heavy rain by Sunday. The snow level is expected to rise to about 6000 feet before precipitation decreases and a more northwesterly flow with cooler air allows snow levels to drop back to pass elevations.
The first time either melt water or rain is introduced to snow, it causes it to become unstable. A lot of weight is added quickly and the water percolates down to a weak layer or harder bed surface.
Expect the avalanche danger to slowly increase with any new snow and wind but as soon as it starts raining, the avalanche danger will rapidly increase to CONSIDERABLE possibly HIGH. Keep informed of weather developments and get off and out from under anything steep enough to slide.
Dudley issues the next advisory on Tuesday, December 23.
Enjoy the snow and be safe this weekend.