Triggering an avalanche is likely today on wind loaded slopes. New snow and steady west winds have built wind slabs on upper elevation east aspects. Storm slab is possible at mid and upper elevations.
If you see a smooth pillowy slab or experience cracking and collapsing, stick to slopes below 33 degrees.
Sun and warm temperatures may cause wet snow avalanche activity this afternoon on south aspects.
Seeley lake has received nearly a foot of new snow in the past 48 hours. This snow is low density but may form a soft slab today, especially if temperatures warm slightly. Triggering a storm slab is possible on convex breakovers or slopes over 36 degrees. Remember, even a small avalanche into a terrain trap like a gully, roadcut, or bench could bury you.
Since Tuesday morning, nearly a foot of low density snow has fallen in the Seeley Lake zone. Ridgetop winds have been steady out of the west in the moderate to strong category. The combination of new snow and wind has created wind slabs along east facing ridgelines. These slabs are sensitive, and human triggered avalanches are likely. Watch for loading at convex breakovers, cross loading in gullies, or at cliff base. An avalanche in fresh wind slab also has the potential to release stubborn wind slab from last weekend, resulting in a larger, more dangerous avalanche.
Wind slabs can be identified by their smooth rounded appearance. Watch for shooting cracks, collapsing, or a hollow feeling slab. If you encounter any of these, stick to slopes under 33 degrees.
(2/1/2023)
Shooting cracks at ridge top and the left flank of the resulting wind slab avalanche.
Photo: Jeff Carty
Seeley Lake and the Rattlesnake have received the most snow in the past two days. In Seeley Lake, a foot of low density snow has fallen since Tuesday. As you move south through the Bitterroot, there is significantly less new snow. Winds, however, have been consistent through all zones, with ridgetop winds steady out of the west. Wind speeds have been ideal for transporting snow, especially the low density snow that fell in Seeley Lake.
Wind slab is the primary concern today in all zones. Observers reported two feet of snow available for transport and a sensitive slab forming on east aspects. In Seeley Lake and the Rattlesnake, fresh wind slabs could be up to 3 feet deep and capable of avalanches D2 in size. Any fresh wind slabs are going to be sensitive, and human triggered avalanches are likely. Last weekend, we saw a significant natural avalanche cycle on wind slabs on all aspects. Triggering one of these old slabs is unlikely at this point. An avalanche on the new wind slab may have enough force to release an old slab, resulting in a larger avalanche.
Clear skies and warm temperatures today may result in some wet snow avalanches. Often, when we see warming and sun on fresh snow, it leads to widespread but small wet loose avalanches. If you see indicators that the snow is getting wet or losing strength, stay out of avalanche terrain on affected aspects.
We have removed the persistent slab concerns in Seeley and the Rattlesnake, as well as the deep persistent slab from the southern Bitterroot, from the problem descriptions. These layers are gaining strength and have been tested thoroughly over the past week without any reported avalanches. In the southern Bitterroot, there are still areas at upper elevation north aspects with weak basal facets. It is unlikely to trigger an avalanche on this layer but remains a low probability, high consequence problem. In the Rattlesnake and Seeley Lake, any buried surface hoar was likely destroyed during the natural avalanche cycle in these zones last weekend.
Please let us know what you are seeing today by submitting an observation.
Ski and ride safe.
