Avalanche Forecast for the Idaho City Mountains

Bottom Line

Three weeks of extended snow drought dominate the development of the snowpack. The melt-freeze and rounded facets layers continue to sinter. This is reflected in snowpack densities exceeding 20%.

PWL avalanche releases in the Idaho City Mountains are UNLIKELY. Pockets of poor snowpack structure continue to be found at isolated locations. Occasionally, a pocket with poor snowpack structure surprises us during column testing.

The isolated PWL cannot be dismissed until we have significantly more snow and the pre-January PWL layers are no longer accessible to triggering.

Avalanche Problem #1:

Wet-loose at steep northerly slopes.

The highly unusual day and overnight temperatures above the freezing level will allow the snowpack to become moist and saturated in isolated spots.

Reactivity: Stubborn

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

Avalanche release likelihood: Possible

Avalanche Problem #2:

Isolated Propagating (PWL) layers present on shady, sheltered north-facing slopes above 7,200 feet might become more reactive due to the current unusually high temperatures.

Reactivity: Unreactive

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

Avalanche release likelihood: UNLIKELY

Forecast Confidence:

Low confidence.

The presence of liquid water is a source of uncertainty. This is further accentuated by the unusually high temperatures expected to affect the snowpack over the next few days.

Snow and Riding Conditions:

Variable snow surfaces. Wet snow skiing.

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

ASG Snowpack Development Chart

ASG Technical Tip

Avalanche Science Guides measures and tracks "the depth" of weak layers. Depth is different than the height of the weak layer. Depth is measured perpendicular (normal) to the snow surface. Depth is, in fact, the shortest distance between snowpack layers, and it is independent of slope angle.

The height of the new snow is denoted as HS (height of the snow). Height is measured using the plumb direction regardless of the slope angle where the snow height observation is made. Height is a function of slope angle and increases with it, even though the depth remains constant.

Tracking the appropriate weak-layer depth is important because it allows us to attribute it to wind loading, higher snow deposition due to elevation, or snow settlement caused by rounding. This is not easy to do when only tracking snow height.