Bottom Line
From Monday to Thursday, snowfall in the Idaho City Mountains could total 20 to 25 cm.
The first storm is on Monday, with light and wet precipitation. A second more productive precipitation event will reach the Idaho City Mountains by Wednesday. The second storm will be accompanied by stronger SW winds and shifting to the NW post-storm. Temperatures will be on the milder side, with heavier and wetter snow at elevations below 7500 feet.
Wind slab and storm slab avalanches are expected in steep terrain. Deep slab instability cannot be ruled out in steep, northern-aspect terrain.
Avalanche Problem #1: Wind Slab
By Thursday, there will be enough snow available for transport and build wind slabs capable of burying a skier (size D2).
Reactivity: Reactive.
Spatial Distribution: Specific. Snow deposition areas through the north and south aspects above 7000 feet.
Avalanche release likelihood: Likely
Avalanche Problem #2: Storm Slab
If snow totals exceed the 25 mm of SWE, there will be enough load for storm slabs to become reactive. Precipitation totals at the Idaho City Mountains do not suggest that the two storm precipitation will be sufficient to break the 25 mm SWE critical threshold.
Reactivity: Stubborn.
Spatial Distribution: Widespread. Expected at steep slopes in wind-sheltered terrain where fragile precipitation crystals from the first storm were preserved.
Avalanche release likelihood: Possible
Avalanche Problem #3: DEEP Slab (PWL)
Additional snowfall this week will bury the surface hoar and near-surface crystals that failed to release during the instability cycles on February 16 and 27. These weak layers are becoming harder to trigger due to rounding, sintering, and the melt-freeze process affecting the top 50 cm after last week's warm temperatures.
Reactivity: Stubborn.
Spatial Distribution: Isolated.
Avalanche release likelihood: Unlikely
Forecast Confidence
Moderate confidence.
The snowpack is transitioning to a spring snowpack. With very little "cold content', instabilities are expected to be short-lived.
Snow and Riding Conditions
Variable snow surfaces, from carvable and supportable preserved powder at northern aspects to torturous crust at the slightest solar-impacted terrain.
ASG Snowpack Development Chart
ASG Technical Tip
Most avalanche fatalities occur in medium-sized avalanches, rated D2 and D2.5 in destructive size. D2 avalanches are not energetic enough to destroy structures or cars, or even knock down trees.
These D2-size avalanches bury victims to an average depth of 1.2-1.5 meters, depending on whether it's treed or alpine terrain. The avalanche debris zone is generally well defined and has an area of 50 square meters. The debris angles are measured by ASG at various geographies and snow climates are in the 24 to 28 degrees.
The ASG conducts companion rescue simulations on slopes with a 26-28-degree slope angle, buries a rescue target at a depth of 1.2 meters, and flags debris zones with a 50-meter diameter. The distance skied from the simulated starting zone to the debris zone is in the 130-meter range. ASG demands teams of 2 rescuers to complete companion rescue simulations in less than 5 minutes.
