Friday is the day that I have the least confidence about what will happen. As the low pressure system continues to track east, one model (ECMWF) shows a front trailing behind it and settling just south of Watkins Glen, bringing some drier and and pushing rain to the south. Another model (GFS) holds the front well to the north, keeping a warm and moist air mass over the track where thunderstorms will be ripe to develop. I'm going to lean the forecast toward the latter model, but with a lower chance of rain than it suggests. Right now, I can see scattered afternoon showers and storms developing on Friday, but I don't see an organized system that will bring a lot of rain all day. I expect that whatever I forecast now for Friday is going to change in the next few days, so stay tuned.
Saturday looks like the most ominous day of the event, as another stronger low pressure system will be tracking northeast across the Great Lakes through the day. There will be plenty of moisture deep into the atmosphere ahead of the system, which will help produce numerous showers and storms around the area. It is likely that there will be rain at the track on Saturday, and probably some thunderstorms too. Timing is too uncertain to determine which sessions will be impacted, and it is too early to tell how much rain could fall. But as it stands today, I can see at least a moderate impact to the on-track action, with some stoppages or delays in qualifying or races possible.
The low pressure system will pull a cold front through the area on either Saturday night or Sunday. This is where I am uncertain about timing details. If the front moves through on Saturday night, then the entire race on Sunday will probably remain dry, with decreasing clouds through the day. If the front is slower, then rain could affect at least the early stages of the race, which begins at 10:10 am EDT. Right now, I think the earlier timing is more likely, but I am including a slight chance of rain in the morning in case things slow down.
This is a complicated forecast, so I'll be making adjustments to it through the week. Be sure to check back here, and follow our Racecast Weather social media feeds on the right.