By Doug Schneider

Dry weather is likely for the Hy-Vee INDYCAR weekend at Iowa, but hot temperatures will be the main impact. The weather pattern is expected to change little through the weekend, with high pressure dominating much of the Great Plains. This should result in mostly sunny skies and a rain-free weekend. With temperatures reaching into the lower 90s on Saturday and Sunday, the heat Index may reach to near 100 degrees. If you're going to the Speedway, be prepared for the hot conditions by drinking plenty of water and taking frequent breaks in the shade.

By Doug Schneider

The chance of weather impacts at Road America has risen on Saturday as an upper level disturbance will cross the area during the day. 

Friday will be a nice day with plenty of sunshine and pleasant temperatures near 70. It will be quite breezy, with a northwest wind between 15 and 25 mph, with gusts around 30 mph at times. 

Rain is expected to arrive at Road America around noon on Saturday, and persist for several hours. There is a small chance that there could be a few thunderstorms as well, but the main impact will be the rain showers. Total rain amounts on Saturday afternoon will likely be around a quarter of an inch, possibly up to a half inch. I expect with this amount of rain, there could be some delays to some of the sessions. 

Sunday's weather looks much better behind the departing low pressure system, with mostly sunny skies and highs in the lower 70s. 

By Doug Schneider

Overall, there is likely to be good weather for INDYCAR weekend at Road America, but there is a small chance of seeing a light shower or two on Saturday and Sunday afternoons. 

High pressure will be building over the region on Friday behind a departing low. The pressure difference between these two systems will result in breezy conditions on Friday, with a west wind between 15 and 20 mph, gusting to 30 mph at times.

An upper level low pressure system is expected to approach from the northwest and cross the region on Saturday afternoon through Sunday afternoon. A little instability from this system will result in some scattered to isolated showers popping up both afternoons. These showers should be light, and the chance of thunderstorms is low, but cannot be ruled out entirely. Temperatures will be pleasant, with daytime highs in the upper 60s to around 70.

By Doug Schneider

Not much has changed since my initial forecast for the Detroit Grand Prix, but the timing of rain has come into better focus. 

A cold front will be approaching the area on Saturday, but I expect that all the racing can be done in the dry that day. Showers are expected to move into Detroit late in the day, around or after 6 pm. The IMSA race is scheduled to end at 5 pm, so the chance of impacts is very low. Of course, the rain may arrive a little earlier than expected, but I think the chance of that is low. 

Saturday night will have rain showers moving through, with a tenth to a quarter inch of rain expected. This rain is expected to exit Sunday morning, mainly by 8 or 9 am. The INDYCAR morning warm-up session is at 9:30, so there is a chance of running it in wet conditions if the showers are slower to exit that expected. After the rain exits, clouds will gradually decrease, and the weather for the race looks good, with partly sunny skies and temperatures in the 70s.

By Doug Schneider

Overall, the Detroit Grand Prix should have good weather, with just a slight chance of a shower on Sunday. 

A large high pressure ridge will be over the Great Lakes region on Friday, providing mostly sunny skies and comfortable temperatures and humidity levels. This ridge moves east on Saturday, which will bring increasing clouds through the day, and warmer temperatures with a southerly flow. There is a small chance that some showers could spread into the area in the evening, but most of this should hold off until after the on-track activity has ended for the day. There's a good chance of showers on Saturday night as an upper level trough moves through the region. For Sunday, the models begin to differ, with some keeping the trough over the area, which could lead to some showers. Other show the trough moving away quickly, resulting in a dry day. For this initial forecast, I will have just a slight chance (20%) of rain due to the uncertainty of timing with this system. Overall, I think there will be a very low chance of impacts on the racing. 

Check back later in the week for updates, and follow @RacecastWx on X and RacecastWeather on Facebook and Instagram.

By Doug Schneider

The models are starting to come into better agreement on some aspects of the forecast for Sunday at IMS, in particular the timing of two main rounds of showers and thunderstorms. A complex of thunderstorms is expected to develop in Iowa and Missouri tonight, then move east across Illinois Sunday morning. This first round of storms is expected in the IMS area around 2 pm, give or take an hour. The earliest potential arrival time of storms is noon, and the latest is around 3 pm, but 2 pm appears the most likely time of arrival. These storms may last about an hour to an hour and a half. With that expected arrival time, there may be enough time to race for about an hour to maybe an hour and a half before rain arrives. If the start time can be moved earlier, that would be ideal, but I don't know how likely INDYCAR is to do that. Moving it earlier would increase the chance of getting an official race in.

Update:  Here is what IMS President J. Douglas Boles had to say about moving the start time earlier - Question: Would you ever move up the race? “I don’t think so. Because people know when it is. We’ve never really moved it up. Now I say that, I can see where we might say, ‘Look, people are basically in their seats by noon and ready to go.’ If for whatever reason we thought moving it up by 10 or 20 minutes, because right now I think the Green flag is roughly 12:35 p.m. so if we said, ‘Hey, we’re going to move the green flag up to 12:15 p.m.’ I can see that potentially happening, but I don’t see us making a wild change to say ‘Hey we’re going to start it early or whatever.’ So plan on it starting when it’s supposed to start.”

The biggest uncertainty is what happens after the first round of storms moves through. Will there be a dry period of several hours, or will there be scattered on/off showers and storms through the mid to late afternoon? This will make all the difference in the chance to dry the track and restart the race. There may be a dry period for several hours that would allow time to dry the track and complete the race, or it could be a frustrating situation where drying attempts are interrupted by a passing shower or storm. Perhaps I'm being optimistic, but I think the most likely scenario is a period of several hours without rain, likely between 4 and 7 pm. That is what a majority of models are indicating, but they aren't perfect.

A second round of storms is expected in the evening, arriving around 8 or 9 pm. Since sunset is around 9 pm, I would guess that 8 pm might be the latest time they would run, but I'm not sure about that. I think storms in the area will likely end any running around 8 pm anyway. These storms could be strong to severe, with damaging wind gusts and large hail, and an isolated tornado cannot be ruled out. The NWS Storm Prediction Center has an Enhanced Risk (level 3 of 5) of severe storms for areas along and south of I-74. For those remaining at the track that late, be prepared to find sturdy shelter from these storms. 

I'll be posting radar updates through the day on our X account, @RacecastWx.

By Doug Schneider

In the ten years that I've been doing race forecasts, this is by far the most difficult Indy 500 forecast I've done. There is still uncertainty about the exact timing of when showers and thunderstorms will move through the area, but I have higher confidence today than I did with my forecast a few days ago. The bottom line is that I do expect there to be racing on Sunday. I also expect rain to impact at least some of the race. This is why I have a "Low" impact on Sunday - I expect delays due to rain, but I think there can be enough racing to make the race "official". 

For the races this evening at IRP and the Carb Day concerts, scattered showers and thunderstorms are expected to be in the area between 6 pm and 10 pm. This should be just after the concerts, but the IRP races may be affected. With scattered coverage expected, it's possible the storms could avoid IRP completely. But if you're at IRP this evening, stay weather aware and know where to find shelter.

A thunderstorm complex is expected to be moving across Iowa and Missouri on Saturday night, and will likely be crossing the Mississippi River near daybreak Sunday morning. It is expected to hold together as it moves across Illinois Sunday morning. The question is when it will arrive at the Speedway. 

Here are the two possible scenarios that may happen:

1) Showers and thunderstorms from the west move through in a window between 11 am and 2 pm, then there is a window of several hours when track dying will be possible, and much of the race can be completed before another round of showers and thunderstorms arrives around 7 pm to 9 pm. 

2) Showers and thunderstorms from the west arrive in the area around 3 pm. This would allow for a good portion of the race to be completed before the rain arrives. 

In my experience forecasting thunderstorm complexes like this, the faster speed of the system is usually what happens. The models are often too slow with them. So I expect that scenario 1 is the more likely of the two. In  either case, I do think there will be a good chance of getting at least part of the race completed on Sunday.

Another concern is the potential for them to be strong to severe in the afternoon and evening. The NWS Storm Prediction Center has the area in an Enhanced Risk for severe weather (3 on the scale of 1 to 5). If the first scenario plays out, the initial round of showers and storms will not be severe, although lightning will be a threat. It is the second round that may move through later in the day that will have the potential to produce damaging wind gusts and large hail. Hopefully the race will be completed and the track emptied out by then.

If it is necessary to run on Monday, the weather looks good by the afternoon. A few morning showers are possible, but the rest of the day will be dry with a high in the mid 70s and mostly sunny skies. 

Be sure to follow @RacecastWx on X, and RacecastWeather on Facebook. I'll be posting updates there during race day.

By Doug Schneider

The timing has shifting for a cold front that will pass through Indianapolis, with a later timing from my initial forecast. The front is now expected to cross the area on Friday, which will result in numerous showers and thunderstorms Friday afternoon. I expect there will be enough time in the late morning and early afternoon to get practice done (between 11 AM and 1:30 PM), and possibly the Pit Stop Challenge, but conditions do not look favorable for the evening concerts. 

Dry air will build in behind the front for Saturday, so I expect that to be a dry day. I can't completely rule out a shower but I think the chance is low enough to have no chance of rain mentioned in the graphic. 

On Sunday, an upper level disturbance will move across the area. The timing of this disturbance will be key to any delays to the race, and unfortunately, the timing is not yet clear, as there are some model disagreements. I'm going with an optimistic forecast shown by a few models that has most of the rain mainly occurring in the morning, moving out in the early afternoon. In this scenario, there could be delays to the start of the race due to track drying efforts, but the race should be able to be held in full before dark. The more pessimistic scenario is that the rain arrives in the afternoon, which would push the start back too far to run the entire race on Sunday. If there are storms in the afternoon, the instability could be enough to cause strong to severe storms. Confidence is low on which scenario will occur, so check back here for updates as the timing comes into better focus.