A low pressure system is expected to track across Iowa and southern Wisconsin on Thursday, which should bring a chance of showers to Road America. The timing right now appears to favor Thursday morning for the best rain chances, but I can't rule out rain at any time of the day just yet. I think this rain will be mainly light, as the bulk of it will be south of the circuit.
A high pressure ridge will build over the region on Friday, but it won't last long in the fast-moving weather pattern. This is where the forecast gets tricky. Another low pressure system is expected to develop over the Plains, but it appears at this time that it will track farther south than Thursday's system, across central Illinois and Indiana. If it ends up tracking a little farther north, there will be a chance of rain Saturday. I think the dry scenario is more likely at this point, so that's what I'm forecasting.
Sunday appears likely to be dry at this time, but there is one model (GFS) that points toward a weak upper level disturbance crossing the area and bringing light rain. The ECMWF holds the rain off until Sunday night. This far out in the forecast, I don't put a lot of confidence in the ability of the models to accurately forecast the timing of weak disturbances such as this one, so my confidence in seeing rain on Sunday is low. I will go with just a slight chance of rain in the forecast for now.
Stay tuned to updates through the week. For updates on Twitter, follow @Race4caster.