Bottom Line
This forecast is essentially the same as the avalanche forecast released a few days ago. With the caveat that the storm expected to start precipitating in our area by Thursday did not materialize. The snow total for this storm has declined.
A warm winter storm with snow levels near 6000 feet is forecast to precipitate as much as 20 cm of new snow in the Idaho City Mountains over a period of 48 hours ending Sunday morning. The precipitation event commences on Friday night.
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 due to strong (>12 m/s) westerly winds with gusts in the extreme range as the cold front transits the area.
Avalanche Problem #1: Wind Slab
By Saturday 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 Northeast, East, and Southeast aspects above 7000 feet.
Avalanche release likelihood: Likely on steep complex terrain (as defined by ATES 2.0).
Avalanche Problem #2: Propagating Weak Layer (PWL)
It is possible to have isolated pockets of the mid-February surface hoar and near-surface facets that were responsible for a significant natural avalanche cycle.
In addition, we cannot rule out the possibility of facet development above or below the multiple surface-melt-freeze layers buried in the snowpack, as shown in the snowpack model for Pilot Peak.
Reactivity: Stubborn.
Spatial Distribution: Isolated. Deep north and sheltered slopes.
Avalanche release likelihood: Likely on steep complex terrain (ATES 2.0).
Forecast Confidence
Low confidence.
The strong westerly zonal flow to the north of our area will influence the Idaho City Mountains for a much shorter period of precipitation, resulting in reduced snowfall totals. The strong winds add to the uncertainty of this forecast.
Snow and Riding Conditions
Elevations above 7000 feet will provide opportunities for boot-high 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.
Use this link to access the ATES 2.0 paper presented at ISSW:
https://drive.google.com/file/d/1kNGGNl5crOcuq36YSZnE7xiwDQga1lXW/view?usp=drive_link