500 millibar heights indicate the system forecast to produce accumulating snow over the North Plains is moving onshore. This system will move over the North Rockies, weaken, and swiftly move across the North Plains to produce accumulating snow. Tonight's 0z Models should provide the 'final' and most accurate estimates for accumulating snow.
As for right now, today's 12z GFS shows lower amounts than our previous post where the GFS was estimating over a foot of snow possible for extreme SW South Dakota. Below is the 12z maximum snow depth forecast.
The extreme SW South Dakota will still have a very isolated spot of a foot or possibly more, while the rest of South Dakota will range from 1 inch to 5 inches. Minnesota and Wisconsin will get less snow than is currently forecast, but it will depend on how strong the system is when it crosses the Rockies.