Cooke City

While most slopes are stable, 1-4” thick, isolated wind drifts exist on some slopes at higher elevations. These will stabilize more slowly than normal as they sit on weak facets. These shallow avalanches could be hazardous in high‑consequence terrain. Choose a safer route around drifts in steep or extreme terrain where a small avalanche would be dangerous. In general, wind-sheltered terrain will have the softest snow surfaces and the safest avalanche conditions.

The primary instability of concern throughout the forecast area is wind slab avalanches breaking in the upper foot of the snowpack on slopes with fresh drifts. The depth of these slabs of wind-packed snow varies based on the amount of snow that fell this weekend and the strength of the wind afterward.

The old snow surface weakened dramatically during the latest period of sunny skies and cold temperatures (near-surface faceting video). Wind slabs sitting on these sugary facets will stabilize slowly. Areas near ridgelines and below cornices, and at convex rollovers, are often wind-loaded and more likely to be unstable. A stiffening or texturing of the snow surface indicates drifted snow. Shooting cracks and recent avalanche activity are the telltales of instability.

The balance to strike is deciding how dangerous these wind slab avalanches are on a given slope, as they range from 1-3” thick where it snowed less this weekend (conditionally dangerous based on terrain) to 6-12” thick where it snowed more (more dangerous on more slopes). Either avoid wind-drifted slopes or evaluate the thickness (potential hazard) of wind slabs with a pole or foot plant, or a snow pit, and adjust your exposure as needed.

This weekend, three to 6” of low‑density snow fell in the Bridger Range, Hyalite, and localized areas in the Northern Madison Range. Skiers and climbers triggered sensitive wind slab avalanches that broke 4-12” deep and 10–50 feet wide (East Fork of Hyalite climbs, Divide peak observations, Mt. Blackmore obs. 1, Mt. Blackmore Obs. 2, Bridgers observation, Bridgers 2). Seek out wind-sheltered terrain where the snow surface is softer, and avalanche conditions are safer. Avalanche danger is MODERATE in the Bridger, Northern Gallatin, and Northern Madison Ranges.

Elsewhere in the forecast area, up to 2” of snow fell this weekend. While most slopes are stable, yesterday in the Southern Madison Range, we found 1-3” thick, isolated wind drifts sitting on weak facets near ridgelines (video), and riders in Tepee Basin triggered a thin, but surprisingly wide wind slab avalanche on Sunday (details and photos). In Cooke City, guides noted shooting cracks 3-4” deep (observation). These could be hazardous in high‑consequence terrain. Choose a safer route around drifts in steep or extreme terrain where a small avalanche would be dangerous.

A second, and less common, concern is dry loose avalanches, or sluffs, running within the weak, faceted snow surface. These will be small and only dangerous in steep, technical terrain. The danger is LOW in the Cooke City, Lionhead, and Island Park areas, and the Southern Madison and Southern Gallatin Ranges.

*The Friends of GNFAC and GNFAC propose to replace an old weather station near Island Park adjacent to Sawtell Peak for measuring snowfall and other parameters. The Friends of GNFAC are applying for an RTP grant through the Idaho Department of Parks and Recreation for about $18,000. If you have any comments regarding this action, please contact Mark Staples at [email protected]