Bottom Line
A warm winter storm with snow levels near 6000 feet is forecast to precipitate as much as 25 cm of new snow in the Idaho City Mountains over a period of 72 hours ending Saturday morning.
The new snow is expected to bond well with the variable snow surfaces in the current snowpack.
Wind slabs are expected at elevations above 7000 feet, as winds increase on Thursday to moderate (> 7-8 m/s) with strong gusts (> 11-12 m/s).
Avalanche Problem #1: Wind Slab
By Thursday morning, 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, northeast, east, and south aspects above 7000 feet.
Avalanche release likelihood: Likely on steep complex terrain (ATES 2.0).
Avalanche Problem #: Propagating Weak Layer (PWL)
It is possible to have isolated pockets of near-surface facets (NSF).
NSF not destroyed by solar radiation or by temperatures above freezing levels might get buried by new snow.
And the perverse new reality facing us nowadays, of facet development above or below the surface melt-freeze layers.
Reactivity: Stubborn.
Spatial Distribution: Isolated. Deep north and sheltered slopes.
Avalanche release likelihood: Likely on steep complex terrain (ATES 2.0).
Forecast Confidence
Moderate confidence.
A strong westerly zonal flow might increase the likelihood of higher precipitation rates and totals. This forecast will be updated on Friday as the storm progresses.
Snow and Riding Conditions
Pow snow conditions will be back by Thursday through the upcoming weekend! Snow at 6000-6500 feet will be wet. Elevations above 7000 feet will provide opportunities for memorable pow turns.
ASG Snowpack Development Chart
ASG Technical Tip
It is a good investment in time to review the ATES 2.0 scale released last October 2023.
The ATES has been updated to better reflect the nature of avalanche terrain based on exposure, slope angles, and avalanche release frequency.
For example, as defined by ATES 2.0, complex terrain is characterized by frequent exposure to starting zones and the presence of D2 and D3 avalanches observed annually. Such terrain has moderate to high angles (above 35 degrees), and there are limited options to reduce exposure. This is the terrain where wind slab avalanches forecasted in this advisory will be found.