Flathead Range & Glacier NP

At mid and upper elevations, it's possible to trigger slabs of drifted snow a foot or more thick. In wind-sheltered terrain, sluffs of loose dry snow can pose a hazard in very steep, confined terrain or above terrain traps. Test slopes and the texture of the near-surface snow can give you reliable data about these hazards. Hard over soft? That's Wind Slab conditions. Loose and cohesionless over hard? That a Loose Dry hazard. This is our last daily forecast for the 2020-21 winter. We'll issue conditions updates twice a week through the end of April. 

Strong winds and snow showers have left scattered avalanche hazards across the forecast region. The primary concern is slabs of drifted snow left by an extended period of strong westerly winds. Since Wendnesday, ridgeline stations have recorded several bouts of winds averaging near 20 mph, with gusts of 40 to 70 mph. The Swan and Flathead crests saw the strongest winds, and observers reported plumes of blowing snow off the high peaks in the Flathead Range on Friday.

The winds haven't had much snow to move around, and much of what was available was graupel. At mid elevations in the Swan Range Saturday, I found thin soft drifts near ridges, and in a few spots, older hard slab less than a foot thick. Similar conditions exist throughout the region. The thickest, most dangerous slabs are in at upper elevations, in areas where more than a few inches of new snow accompanied the winds. That's primarily the Swan crest, and the high peaks of the Flathead Range, Lake McDonald valley, and Stevens Canyon. Similar slabs are isolated at mid-elevations. Wind speeds dropped overnight and are forecast to remain light until later this afternoon. With little additional drifting, I expect existing slabs to stabilize.

A second concern that's less widespread across the region are Loose Dry snow avalanches. These can pose a hazard where more than about 8 inches of loose snow sits on firm old snow or melt-freeze crusts. Those conditions are isolated in the Whitefish and Swan Ranges, where recent snow accumulations are generally less than 8 inches except at high elevations. In the Flathead Range on Friday, Clancy found he was able to trigger small sluffs of dry snow on very steep, northerly slopes at mid-elevations. With another 3 to 5 inches of snow Saturday, this hazard will be more widespread in that zone today, with sluffs possible in very steep, wind-sheltered terrain at mid and upper elevations. The debris from these sluffs can be surprisingly dense, so pick terrain that isn't confined or over terrain traps. 

Most windward and sunny slopes have a stout melt-freeze crust that's unlikely to break down today. 

Pro tip: Check back for conditions updates through the end of April. We'll be issuing these twice a week, unless conditions change dramatically enough to warrant more. Your observations can make those more accurate, so let us know what you find on your late season adventures. Your friends in the backcountry community will appreciate those updates too. 

A huge thank your to everyone who's contributed to our forecasts this winter: volunteer field partners, interns Zach, Jeremy, and Sarah, observers, our partners at Whitefish Mountain ski patrol, the Patrol Fund, and the Burlington Northern avalanche program, anyone who shared near miss and accident information or observations, and the Friends of the Flathead Avalanche Center!