A low pressure system is forecast to develop in the lee of the Rocky Mountains early Wednesday and move northeast, just to the south of Wisconsin, towards lower Michigan. The development of this system will be assisted by a decent upper level disturbance. Models are coming into better agreement with the track and strength of the surface low, now leaning toward a weaker solution.
Below is a picture depicting where we think the different precipitation types will focus. Warmer temperatures in far southeast Wisconsin will likely bring a rain/snow mix to areas roughly southeast of a line from Janesville to Port Washington. The best chance for snow accumulation will be to the northwest of this line, where there is a smaller chance of a mix with rain.
The graphic below shows the snow accumulation forecast for Wednesday night through Thursday morning. With this system trending weaker, expected snowfall amounts have decreased. Stay tuned for later updates.
The next image shows the amount of precipitation expected across southern Wisconsin. This is the liquid equivalent of any snowfall along with the rain.