Lionhead Area

The weak layers near the ground just got a big load of snow from this last storm. The last time this happened there were a lot of big avalanches. Avoid all steep slopes today, including crossing beneath them.

Looking at the map today you’ll see a lot of orange (indicating CONSIDERABLE danger in most zones), but that apparent simplicity hides substantial differences across the advisory area. 

In the Southern Madison Range, Southern Gallatin Range and Lionhead area, a big storm has just put a heavy load on reactive weak layers near the ground. The Lionhead area got over 5” of snow water equivalent in this last storm (likely around 4 ft of snow), with 3” of snow water equivalent in the Taylor Fork. The last time this snowpack got a big load, we saw a widespread Persistent Slab avalanche cycle in Lionhead (observation) and large avalanches being triggered from far away in the Taylor Fork (video), so we should expect the same today. Slopes that have already avalanched this year are primed to break again, as shown by Dave and Mark triggering one on Monday (observation). Avoiding all steep slopes (including crossing close beneath them) is the only reasonable plan today in these areas. 

Around Island Park and Cooke City, there has been plenty of recent new snow (3+ ft), but the weak layers at the ground are buried really deeply. You’d have to get very unlucky to trigger a slide on these layers. The chief concern is instabilities within the new snow, particularly where it has been drifted by the wind. Do not take these concerns lightly. With so much new snow, wind drifts will be deep and capable of producing large, very dangerous avalanches. Plan to avoid all steep, windloaded slopes. If you see any cracking or feel collapses, avoid all steep slopes.

In the Northern Gallatin and Northern Madison Ranges, there’s been less recent snowfall and we haven’t seen avalanches breaking on the weak layers near the ground recently. In these regions, the danger is driven by strong west winds and enough fresh snow to blow into dangerous drifts. You are likely going to trigger a Wind Slab avalanche if you get on a steep windloaded slope. Identify and avoid these wind drifts to avoid the bulk of the avalanche concerns. Search out lower angled or non-windloaded slopes for safer riding today.

There has been even less snow recently in the Bridger Range, so Wind Slab avalanches will be correspondingly shallower and less widespread - leading to a MODERATE danger. Still, Dave and Alex found thin, reactive wind slabs yesterday (video). These slides will be most dangerous in steep and technical terrain. Bigger slopes and higher elevation slopes have the most potential for larger slides.