Silver Valley & Bitterroot Mountains

Very dangerous avalanche conditions developed overnight and will last though Tuesday as heavy, wet snowfall transitioned to heavy rain along with strong winds. A potent atmospheric river characterized by near-historic moisture is introducing a “firehose” of moisture into North Idaho and Northwestern Montana. The rain line rose to around 7,000 to 7,500 feet overnight Monday and will saturate recent snowfall and overload pre-existing weak snow layers. It will be very likely for backcountry travelers to trigger avalanches and natural avalanches are likely. Avalanches can break wide across terrain features and run long distances to lower elevations.

Today's advice is simple...avoid avalanche terrain. Weird weather breeds weird avalanche behavior. 

Snow totals over the past 24 hours range 7 to 13 inches across the Selkirk Mountains, and East and West Cabinet Mountains, 5 to 9 inches in the Silver Valley area, and 4 to 7 inches in the Purcell Mountains. Once the  warm tounge of air arrived Monday night, precipitation flipped to rain. Weather stations in the Selkirk Mountains, and East and West Cabinet Mountains report 1.5 to 3 inches of rain in just shy of 12 hours. Silver Valley stations report 1.5 to 2 inches of rain, and generally 0.5 inches is reported across the Purcells. Hawkins Lake just south of the Canadian border is the only site that we suspect didn't receive rain.

There’s a saying in the avalanche business…”your avalanche forecast is only as good as your weather forecast”. As we enter into a period of challenging weather forecasting, it’ll be important to think one step ahead and be willing to make adjustments around your terrain selections. With somewhat limited field observations and number of eye popping test results, there is a fair bit of uncertainty around how much snow volume or water load is going to kick buried weak snow layers into a more reactive state, or provoke a natural avalanche cycle.

One thing we do know is that a worrisome structure exists in the upper snowpack - primarily focused to mid and upper elevations. Multiple faceted mid-storm crust and a layer of larger facets above the wetted now refrozen early-season snowpack highlight the main concerns. Throw in buried surface hoar on north through east-facing slopes - so far discovered in the Silver Valley and West Cabinet Mountains - and we have a multitude of layers to wreck havoc on backcountry recreation.

Although observations have yet to report many propagating results in Extended Column Tests, snow safety teams have had better luck producing avalanches with explosives. These results, while within an operational area, are fairly representative of the potential behavior of a wild snowpack, and a forward context of the lurking danger below. Despite the lack of propagating results, Compression Tests have repeatedly failed with moderate force in any one of these buried layers of concern. Now stack thick dense and/ or an inverted slab on top and the added weight of a rider or machine may be what’s needed to nudge the snowpack over the edge.

Despite the much-needed recent snowfall, coverage remains thin, particularly at lower elevations and on southerly-facing slopes. Heavy rain Monday night may have erroded lower elevation snow cover and access. Additionally, early-season hazards—rocks, stumps, downed trees—are lurking just beneath the surface. Invisible enough to catch you off guard, shallow enough to abruptly end your day if you’re skiing or riding fast, or lead to a bad outcome if you get knocked off your feet in a slide.