Avalanche Forecast for the Idaho City Mountains

Bottom Line

The recent snow has been settling rapidly, by up to 10 cm in 4 days, under temperatures between -5 °C and the freezing level. Current conditions have favored the rounding and sintering of new snow on old-snow surfaces.

We are in a transition phase, during which Propagating (and persistent) weak-layer avalanche releases in the Idaho City Mountains are becoming unlikely.

Avalanche Problem #1:

Last storm (5 days ago) snow over propagating weak crystals (PWL).

Reactivity: Stubborn

Spatial Distribution: Isolated 

Avalanche release likelihood: Unlikely

Forecast Confidence

High confidence.

Calm weather has allowed the snowpack to relax (by more than four days) and uniformly sinter the recent snow to multiple old surfaces and varying facet layers.

Snow and Riding Conditions

Fun snow!

ASG Snowpack Development Chart

ASG Technical Tip

The snow settlement tells us a lot about snow densification. This densification of snow results from multiple processes, such as snow crystals rounding and the formation of bonds between crystals. 

When precipitation crystals, or hexagonal facets, or planar feathery surface hoar lose their terminations (arms) due to the inherent process of nature minimizing surface area by sublimating sharp edges and depositing water vapor into the core of the crystal. As snow rounds, its porosity decreases, and its density increases.

Snow crystal bonding, also called sintering, is recognized when the slab and weak layers become harder (less cohesive). When the hardness of weak layers exceeds the four-finger hardness, it is typical to observe stubborn reactivity in the snowpack.