The mountains of the Kootenai National Forest have been loaded with new snow by multiple small storms since last Thursdays rain event. At elevations above 6,000' this new snow has multiple density changes and weak layers that could produce soft slab avalanche over 1' in depth. These avalanches will be more likely and more destructive on leeward terrain (north and east aspects) due to light wind loading that occured during the storm cycles.
BOTTOM LINE: AVALANCHE CONDITIONS MAY BE VERY DANGEROUS AT ELEVATIONS ABOVE 6,000' UNTIL THIS NEW SNOW HAS HAD TIME TO SETTLE AND STRENGTHEN. USE CAUTION AND PAY ATTENTION TO CHANGING CONDITIONS AND SNOW DEPTH AS YOU GAIN ELEVATION. STEEP SLOPES OVER 30 DEGREES SHOULD BE AVOIDED AT THESE UPPER ELEVATIONS.
For those riding close to the State Line or in Idaho country gather some additional info by checking out the Panhandle Forecast below:
On Tuesday February 21st we traveled to Shaw Mountain via the Libby Creek drainage. Snow conditions varied drastically with elevation, the one consistency was a very firm, thick rain crust that developed during last Thursdays rain event(10-12" thick). This rain crust can be found at all elevations. As we ascended from the valley floor at 4,000' the snow became progressively deeper, at 6,000' we began to notice thin surface layers breaking loose under our skis. The higher we climbed the deeper these new storm slabs became, we ended our ascent at 6,800' at the ridgeline where the slabs on south aspects were 8" thick and well over a foot thick on leeward north and east aspects. We experienced on audible and concerning collapse in the snowpack just below ridgeline.
Stability tests showed reactive layers in the new storm snow at 12" and 15" below the surface. These failures in the snow were the result of density changes and some thin weak layers that developed between snow cycles. The takehome message: High potential for triggering a storm slab 12-15" thick above 6,000' in elevation. North and Easterly aspects are likely to be more sensitve and hazardous due to some light wind loading as well. As precipitation diminishes and temperatures cool off these slabs will have the opportunity to settle and strengthen, I will be going out again on Thursday and will monitor the strength of this storm snow.
Other notable avalanche observations yesterday were the evidence of slides that appeared to have released during the rain event on the 16th. There was one deep crown line observed on Twin Peak on a north aspect in steep rocky terrain and evidence of multiple loose wet slides that occured during the rain event.
Backcountry Forecast from NWS Missoula issued:
300 AM MST Wed Feb 22 2017
Colder air will settle over the region for the remainder of the
week into the coming weekend with snow levels down to valley
floors. Periodic snow showers will be common, most widespread
during the afternoon hours across the higher terrain.
--------------------------- 5000-7000 FT ----------------------------
Today Tonight Thu
Cloud Cover 85% 85% 85%
Hi/Lo Temps 26 to 32 13 to 19 24 to 30
Winds(mph) W 7 W 4 NW 4
Precip Chc 50 40 50
Precip Type sno/shr sno/shr sno/shr
Liquid Amt 0.07 0.03 0.06
Snow Ratio(SLR) 18:1 19:1 20:1
Snow Amt(in) 1-3 0-1 1
Snow Level 2000 1500 500
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.