East Cabinet Mountains

An Avalanche Warning is in effect from Sunday 6 AM to Monday 6 AM.Very dangerous avalanche conditions have developed from wet, dense snowfall and moderate to heavy rain saturating the snowpack and will last through Monday morning. The snow line will likely rise to between 6,000 and 7,000 feet Sunday afternoon-evening. You can very easily trigger avalanches large enough to bury or kill you, and some will release spontaneously. Avoid travel in avalanche terrain during this period.

Wild weather often breeds unusual avalanche behavior. 36-hour snowfall totals around 5,000 feet and higher range 6 to 12 inches of very wet, dense snow - 17 to 25 percent snow densities. Liquid water input so far is 1 to 2 inches over the same timeframe and most elevations around 4,000 feet and lower have received all rain. Another potent slug of warm air arrives Sunday afternoon and drives the snow line higher in the sky. An above mountain top rain event will likely pan out for the Bitterroot Mountains while the highest terrain across the Northern Mountains has the best odds of being spared the major snow wetting event. 

By Monday morning, the snowpack in some places could hit the 3 to 4 inch watermark adding an insurmountable load to persistent grains that have not disappointed us in terms of their lingering sensitivity since burial on January 31. 

Strom slab densities are a significant shift from the 5 to 7 percent storm snow that accumulated over the last 10 days or so. This inverted layering will make newly formed slabs touchy, and you may be able to provoke avalanches on lower-angled slopes than typical. As you move closer to the treeline and above, deeper and harder slabs more capable of producing large, terrain wide avalanches come into play. Triggering a slide that spans adjacent terrain features or those that fail naturally are more likely to run long distances into mature forests and cause timber damage - especially where a slide initially fails in upper snowpack layers then steps deeper into persistent grains several feet deep.

Weak layers - surface hoar, faceted grains, and a faceted crust - two to three feet deep are the culprit of lingering instability in the upper snowpack. Snowpack tests on slopes near treeline down to about 5,000 feet continue to produce ongoing failures in these weak grains. Well-preserved and upright surface hoar is found on north to east-facing slopes, while southeast through south to west-facing slopes harbor a breakable crust with facets looming above and below. If the snowpack undergoes a prolonged period of steady rain, the wetting front may advance deeper in the snowpack to the January Drought Layer (JDL). If water reaches this interface, we may be entering the Wet Slab avalanche realm of higher uncertainty around the exact moment a slope fails.

If you decide to head into the mountains today, be ready for just about anything. Keep things simple and limit the temptation to thread the snowpack-terrain needle. Avoidance is the best card in the deck for days like this.