Avalanche Forecast for the Idaho City Mountains

Bottom Line

The extensive surface hoar observed in recent weeks has been buried by Wednesday, January 28th, 5-10 cm of NEW snow. An additional 4-6 cm of snow may fall on January 29th.

The surface hoar (SH), ranging from 5-10 mm in size, is also above another layer of diurnal recrystallized snow (NSF). The SH and NSF will become worrisome weak layers once snowfall returns to our area and the snowpack is loaded.

The top 20-30 cm of recrystallized snow on north-facing and sheltered slopes is uncohesive on slopes above 40 degrees. Dry-loose avalanches, behaving like powder sloughs, are LIKELY in steep terrain.

PWL avalanche releases in the Idaho City Mountains are UNLIKELY. Pockets of poor snowpack structure exist, fourtanely they lack reactivity. This problem cannot be dismissed until we have significantly more snow and the PWL layers at 60-70 cm are no longer accessible to triggering.

Avalanche Problem #1:

Dry-loose at steep northerly slopes.

The 3-week diurnal cycles and recent cold spell are responsible for the widespread development of NSF (Near Surface Facets) and SH (surface hoar) at sheltered slopes. The top 20 cm of recrystallized snow (NSF) has become uncohesive and prone to movement, behaving as a granular material that does not adhere to one another and is typically gravity-driven.

Reactivity: Touchy

Spatial Distribution: Isolated at Extreme terrain (ATES 2.0).

Avalanche release likelihood: Likely

Avalanche Problem #2:
Propagating (PWL) layers present on shady, sheltered north-facing slopes, above 7,200 feet.

Reactivity: Unreactive

Spatial Distribution: Isolated at Extreme terrain ( ATES 2.0).

Avalanche release likelihood: UNLIKELY

Forecast Confidence:

High confidence.

Snowpack is rather uniform in structure above 7,000 feet. Below a depth of 30cm, the snowpack is isothermal, and crystal rounding and sintering have continued unabated. All buried weak layers, including multiple melt-freeze layers, are bonding well.

Snow and Riding Conditions:

Variable snow surfaces, especially at any slope with a hint of solar aspects. 

Shady northerly slopes continue to provide fun riding.

Riding below 7000 feet is not recommended due to poor snow coverage.

ASG Snowpack Development Chart

ASG Technical Tip

The use of the term "stable" is akin to declaring a patient healthy. It is more correct to state that no evidence of a disease or health condition has been identified in a patient.

Generally, avalanche professionals and backcountry skiers refer to a snowpack as STABLE, whereas the commonly used term by Avalanche Science Guides is "with little evidence of instability."