By Doug Schneider

It turns out that the weather will be beautiful for Petit Le Mans, and the remains of Ian will have no impact. See the graphics below for the details.

I am sorry for the bad forecasts I made earlier this week. In my first forecast discussion, I mentioned two possible scenarios with Ian, one that kept it close to the Atlantic Coast, and one that brought it inland across Georgia. I went with the second scenario, and I was wrong. Ian crossed Florida, went back over the ocean, then tracked into the Carolinas. So my bad forecast was good news for everyone at Road Atlanta, and I'm very glad that everyone can enjoy the race with excellent weather. I just have to watch it with some egg on my face. 

By Doug Schneider

​Click images to enlarge

The forecast looks much better for Petit Le Mans today. The forecast track of Ian has shifted to the east, which will mean less of an impact on Road Atlanta. Another positive aspect of this forecast update is that most of the rain will fall on Friday night, with less impacts during the scheduled on-track times.

Here's the NWS forecast rainfall along the path of Ian through Sunday morning:

Road Atlanta is on the edge of the white and light green area. I expect that 1 inch of rain could be a high end amount, but the most likely rain amount will be around a half inch. This is much less than expected a few days ago when Ian was forecast to track directly across Georgia. 

Rain showers are expected to move into the area Friday afternoon, and increase in frequency through the evening. The WeatherTech qualifying session has the potential to have a shower, but I expect it to be light enough to allow the session to be held. Friday night won't be great for campers as rain picks up. Showers will continue to be on and off through Saturday morning, which could impact the morning warm up session. But the frequency and intensity of showers will be falling through the day, and I think all 10 hours of the race can be held without major disruption.

With the track of Ian being farther to the east, wind will not be as much of an impact. It will be breezy every day, with sustained winds of 15 to 25 mph, gusting between 30 and 35 mph at times. Objects will need to be secured to keep them from blowing around, but I don't think this should be a safety issue for campers. 

By Doug Schneider

Key Messages and Impacts:

1) The remnants of Hurricane Ian will track across eastern Georgia on Saturday. Windy conditions will develop on Friday night and continue through Saturday. Sustained winds during this time are expected to be between 15 and 30 mph, with gusts of 40 to 45 mph. Possible impacts from the winds may be tree branches and/or weak trees blown down. This is a potential hazard for campers to be aware of and prepare for. Being in a tent on Friday night under trees may be hazardous; campers should consider finding sturdy shelter.
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2) Rain is expected to spread into the area on Friday evening, with heavy rain at times from Friday night through Saturday. Between 2 and 4 inches is expected during that period, which may lead to flooding of low lying areas and small creeks and streams. There is a creek that runs behind the outer paddock area, past turn 1, and near the corner marshals' camping area. Camping near this creek should be avoided. 

​Forecast Discussion:

The main change to the forecast today is to push the timing of rain from the remnants of Ian later into Friday night and Saturday, to account for the slower forecast speed of Ian (click images to enlarge). 

The National Hurricane Center forecast as of 8 AM this morning is below. For the latest forecast from the NHC, click here.

The forecast has shifted to the east, which is somewhat good news for impacts at Road Atlanta. This track takes the storm inland sooner than if it made landfall father west along the Florida Panhandle. This extra time over land will cause the storm to weaker more before its effects are felt in northern Georgia. Still, it will be getting quite windy starting Friday night and continuing through Saturday. Gusts of 40 to 45 mph are expected, which may be strong enough to blow down some weak trees or tree branches.

​Below is the forecast rainfall graphic from the NWS Weather Prediction Center:

At Road Atlanta, between 2 and 4 inches of rain is forecast. Most of this is expected to fall from Friday night through Saturday afternoon. Avoid camping in low lying areas and near creeks, which will have a better chance of flooding. 

In terms of how the racing will be affected, it will be a question of when a heavy shower passes over the track, and whether the rain can run off the racing surface quickly enough to avoid ponding. I think it is likely that there will be some red flag periods during Saturday's race. It is possible that the rain could ease up enough late in the day on Saturday to allow for improving conditions for racing. But it's still early to pin that down with any confidence. 

Check back for updates, and be sure to follow @RacecastWx on Twitter, and RacecastWeather on Facebook and Instagram.

By Doug Schneider

Click on images below to enlarge

It's going to be a challenging week to forecast for Petit Le Mans. What is now Tropical Storm Ian in the Caribbean Sea is expected to track north and become a major hurricane as it moves into the Gulf of Mexico. Below is the forecast from the National Hurricane Center as of 5 pm EDT Sunday.

To better understand what the forecast cone means, here's a good graphic. 

The current NHC forecast track has the potential to produce significant impacts at Road Atlanta on Friday, Friday night, and Saturday. There are a couple scenarios that will affect how much impact Ian will have on the racing.

Scenario 1 - Ian takes a track toward the eastern edge of the forecast cone, and makes landfall in the Florida Peninsula, somewhere near Tampa, and tracks northeast, staying offshore of the Georgia coast. In this scenario, I expect minimal impacts to Road Atlanta. If this happens, there may be some showers and breezy conditions on Friday, but I think the racing would be able to be held on schedule.

Scenario 2 - Ian takes a track that is in the middle or on the western side of the forecast cone, making landfall along the Florida Panhandle, and into Georgia. If this happens, there may be significant wind and rainfall at Road Atlanta on Friday into Saturday. This could cause major disruptions to the racing schedule, as well as pose a possible threat of downed trees and flooding. This could be a safety hazard to people who are camping. 

As of today, I think Scenario 2 is the most likely one to happen. I don't know what IMSA can do to delay the event or reschedule, but the current forecast track and timing of Ian does not look good for holding a race with a track full of people in tents and campers. 

I've seen some comparisons on Twitter between this year and to the 2015 race. This weather pattern is nothing like what happened in 2015. That year, Hurricane Joaquin was well off the Atlantic coast, near the Bahamas, and a low pressure trough over the central U.S. was drawing moisture from Joaquin to the northwest. There was a band of tropical moisture that produced heavy rain over Road Atlanta, but it was not directly associated with Joaquin. There was also no impact from wind.
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This situation is very different. This is expected to be a major hurricane that makes landfall on the Florida coast, and tracks directly into Georgia. The impacts from this system could be much more significant than 2015, especially in regard to wind. 

It is still early to say that any of this will happen with a high level of confidence, but the potential exists. I will have another post up here on Tuesday at the latest, but I will be posting on the @RacecastWx Twitter account every day with the latest forecast track and possible impacts on the event. 

By Doug Schneider

Overall, the forecast for IMSA weekend at VIR is a pretty typical summer-time pattern for the area, with high temperatures in the mid tp upper 80s and a chance of afternoon showers and thunderstorms each day. But there are some finer details that may raise or lower rain chances each day, depending on how the pattern plays out. 

On Friday, a warm southerly flow will set up across North Carolina and southern Virginia, while a cold front located to the northwest will be approaching. With afternoon hearting, scattered showers and thunderstorms are possible in the area around VIR.

The chance of showers and thunderstorms appears to rise a little on Saturday as the cold front gets closer to VIR. Exactly where the front will be located will affect the chance of rain, which adds to the uncertainty of the forecast. But it does look like Saturday has the best chance of seeing wet conditions at some time in the afternoon. 

Sunday will depend on whether the front can push through the area, or stalls nearby. If it stalls, the chance of rain will be higher. If it pushes through, it will likely be a dry and cooler day. With this uncertainty, I have to have at least a small chance of afternoon showers and thunderstorms for now, but this could change as we get closer to the weekend. 

By Doug Schneider

Today at Road America, temperatures will be rather hot, with an afternoon high expected to reach near 90 degrees. It will fell humid as well, which will put the heat index around 95. 

My confidence is increasing that rain will occur on Sunday, but the impacts on the racing will depend on the timing, which is less certain. I expect two main rounds of showers - one will move through this evening, between 8 pm and midnight, then another round on Sunday morning. This will likely impact the Porsche Carrera Cup and the WeatherTech Championship warm-up sessions. If the showers persist long enough, it could affect the start of the WeatherTech race, which begins at 10:40 AM local time. This round of rain is expected to produce about a quarter of an inch of rain, and it may come down heavy enough to cause some delays or stoppages. 

Additional showers will continue to be a threat through the rest of the day. But these showers may be more on/off and scattered in coverage, so I expect the potential impacts during the second half of the WeatherTech Championship race and the Lamborghini Super Trofeo race will be lower than in the morning. 

By Doug Schneider

The main change to the forecast today is a higher chance of rain on Sunday. Confidence is increasing that a cold front will move through Wisconsin during the day, and bring numerous showers to eastern Wisconsin. While a shower is possible at any time of the day, the most likely time for showers appears to be in the mid to late afternoon. The WeatherTech Championship race will be from 11:40 am to 2:20 pm EDT, so it may end up being dry. The Lamborghini Super Trofeo race at 2:55 pm EDT has a higher chance of seeing wet conditions. A thunderstorm will be possible, but the chance of one at the track is low. While the rain could get briefly heavy, I think it will be manageable to race in, so I have the Impact as Low. I expect that rain amounts will be between a tenth and a quarter of an inch before sunset on Sunday, but with most of that falling after the end of the scheduled races. 

By Doug Schneider

The weather looks great for the majority of the IMSA weekend at Road America, but a chance of thunderstorms enters the forecast on Sunday.

A cold front will pass through Wisconsin on Wednesday night, and a high pressure system building in behind it will provide beautiful weather on Thursday as practice sessions begin. This high will gradually shift east through Friday and Saturday, which will result in a southerly wind developing that will bring warming temperatures each day. As a warm and moist air mass builds over the weekend, the chance of showers and thunderstorms will increase as a cold front approaches the area on Sunday. The timing on the chance of storms is too uncertain to pinpoint this far out, but that should come into better focus later in the week. Right now, it appears coverage will be scattered with Low impacts, and it won't be a wash-out. Check back for updates through the week.