By Doug Schneider

The forecast for Petit Le Mans was extremely difficult due to several different factors in the weather pattern that developed through the week and poor model consistency. But I won't make that an excuse. This was not a good forecast for me, and I sincerely apologize.

When I began to look at the data over a week before the race, the models were pointing toward a weak trough off the east coast and a large ridge over the central states that would push a front through on Wednesday followed by a dry northwest flow aloft across Georgia Thursday through Saturday. Sunday afternoon, some, but not all, of the models started to change their tune, showing a deeper and slower upper trough. At this point, none of them hinted at the existence of Hurricane Joaquin. Gradually the models came into better agreement on a deep trough over the southeast, with Joaquin being positioned east of the Bahamas. By the Wednesday forecast update, I started to push the chance of rain into Friday, but it was not enough as the models continued to show a slower and slower system that would pick up tropical moisture from Joaquin. There was still quite a bit of disagreement among the models on where the moisture axis would be located. I was too slow to jump on the bandwagon, as I was waiting for better model agreement on where the rainfall would be. It wasn't until Thursday's forecast update that I brought in a chance of rain on race day. In hindsight, this was probably a day too late. At least I saved face a little with good forecasts on Thursday and Friday. Better late than never, I suppose.

Here's my forecast week, in GIF form.

Saturday: Feeling good, it's going to be a nice and easy forecast to end the season. 

Sunday: GFS model starts to hint a strong low pressure system developing in the southeast, while other models disagree. 

Monday: Now other models are starting to agree with the GFS, but I remain skeptical. We'll see.

Wednesday: Hurricane Joaquin might come into play. Uh oh.

Thursday: Welp. I messed up.

Petit Le Mans was pretty much like -

By Doug Schneider

 Believe it or not, there is silver lining in this very wet forecast. Yesterday I mentioned that rainfall amounts were expected to be in the 1 to 3 inch range during the race. It appears likely that amounts will be on the lower end of that range, around 1 inch to at most 2 inches, and 3 inches appears unlikely (but still possible).

Here's the situation this morning. There is a band of heavy rainfall oriented north to south across South Carolina, while the rain over Georgia is more sporadic and showery. 

That band of rain is expected to rotate to the west, and be aligned with the yellow line by around 8 pm tonight (Road Atlanta is the red dot). So most of the day will be like this morning, with on/off sporadic showers with a few heavier downpours now and then. There may even be some periods when the rain stops. But as we get into the afternoon, the rain should become more frequent and heavier. The worst conditions during the race will likely be at night. 

A Flash Flood Watch is in effect for the area. Avoid low lying areas and nearby creeks, especially Cooper Creek on the east side of the track (from behind the secondary paddock to turn 6). If you're at the track and leaving Sunday morning, you may encounter flooded roads. Do not attempt to cross are road when water is flowing across it! It doesn't take much water to wash a car off the road and carry it downstream. 

To clarify again, this rain is not directly associated with Hurricarn Joaquin, but Joaquin is helping to supply abundant tropical moisture into the southeast. Joaquin is still east of the Bahamas, and is expected to stay out to sea as it curves north. Here's a satellite image that shows the connection between Joaquin and the low pressure system over the southeast.

I'll be live tweeting weather conditions at the race all day - @Race4caster. If you have a question about the weather, I'd be happy to answer on Twitter. Our live radar link is available at the top of the website.

By Doug Schneider

The forecast is coming into better focus, and there's one thing I'm sure about:

The uncertainty is how much it will rain. Here's a graphic of forecast rainfall from the NWS for Saturday:

Road Atlanta is near the top of the first 7, where the colors change from blue to purple to red. This gives you an idea of how tight the gradient of rainfall is in the area near the track. Just a slight shift of the heavy rain to the east, and Road Atlanta could get only an inch. A slight shift to the west, and it will get 7 inches. As depicted in this graphic, Road Atlanta is looking at 1-3 inches of rain on Saturday. But there is a lot of uncertainty in that forecast amount. 

Let me emphasize that this rain is NOT directly associated with Hurricane Joaquin. There is a low pressure system that is sitting over the southeast states, pulling abundant tropical moisture into the region. As the forecast stands now, Joaquin is expected to stay out in the ocean and not make landfall. 

Today, showers will be on and off throughout the day. The track will stay wet all day, but the rain will be sporadic. By Saturday morning, the rain should be more constant, and it will likely be heavy at times. This will continue through the end of the race Saturday evening. 

If you're camping at the track, I highly recommend that you set up your tent on higher ground. Avoid low lying areas, as they are likely to become flooded. You will especially want to avoid being near Cooper Creek, which runs parallel to the east side of the track, from behind the secondary paddock area past the esses to turn 6. It is possible that the creek will flood. 

Despite the rain, I'm sure everyone at the track will have a good time. Remember, a wet day at the race track is better than a dry day anywhere else.

By Doug Schneider

Without a doubt, this Petit Le Mans has been the most difficult race forecast I've had to make in the two years I've been making race forecasts. What makes this forecast so difficult is the influence of Hurricane Joaquin and its interaction with an upper level trough. The models have been inconsistent with each other and with themselves from one run to the next, because this pattern is highly unusual. There is also likely to be a very sharp line between very little rainfall and extremely heavy rainfall that will cause flooding, and this line is probably going to be somewhere near western South Carolina or eastern Georgia. Forecasting exactly where this line will be is really just a guess until it actually develops. 

Yesterday ended up being dry at the Gainsville airport, although there were some thunderstorms reported within 10 miles. I'm not sure if these affected the track or not. It was certainly sunnier than expected, with the high temperature reaching 81. I expect that there will be much more cloud cover today and cooler as winds will be from the northeast and an upper level low moves closer to the area.

Friday will be cloudy and cool, and it is likely that there will be some light rain or drizzle on and off throughout the day. I don't expect any heavy rain, and rain amounts on Friday will probably be less than a tenth of an inch. 

Saturday is a big question mark. There could be some very heavy rain, or very little rain, depending on how Joaquin interacts with the upper level low over the southeast. Joaquin is going to stay well off the coast Saturday, but the question is whether the upper low will pull some it the moisture associated with it far enough west to affect Road Atlanta. Since it appears likely that there will be at least some measurable rainfall at the track on Saturday, I am raising the rain chance to 60%. However, I still expect that the really heavy rainfall is going to stay to the east, mainly over South Carolina. I base this on my experience with these types of weather patterns. But I'm not confident about that, as this is an unusual pattern. I could be completely wrong about this, and there may be very heavy rain and flooding all day. There are still some models that are completely dry, and others show over 5 inches of rain on Saturday. 

At the end of last season, NASportscar.com had a round table, and we were asked to make a crazy prediction about the 2015 TUSC season. I said: "For my crazy on-track prediction, the DeltaWing will be competitive all season, and will win a wild and wet Petit Le Mans." I should have stuck by that prediction I made nearly a year ago, because it seems like it will be more accurate than the one I made yesterday. 

By Doug Schneider

There Today's weather at Road Atlanta is expected to be cloudy and foggy through the morning, with showers likely to affect the track this afternoon. It is possible that there could be a thunderstorm as well. Around a quarter inch of rain is expected. Highs will be in the upper 70s. 

A cold front will be near the area tonight, and push south of the track on Thursday. The proximity of this front to the track and the presence of an upper level low pressure system will mean that showers are likely again on Thursday. Most of the rainfall is expected to come in the afternoon and evening. For Thursday, another quarter inch of rain will be possible. 

Friday continues to be the day that is most questionable as the weather pattern will be transitioning. The upper level low pressure system will be slow to exit the area, and there will still be quite a bit of low level moisture. This is not a pattern that tends to produce heavy rain. In fact, there may only be a trace of rain or around a hundredth of an inch of rain. This is why I only have a 20% chance of measurable rain. I want to emphasize that the majority of Friday is likely to be dry, and I don't expect that what little rain there is will have much impact. It will be cloudy and fairly cool all day, with high in the upper 60s.

Clouds will be around for most of the day on Saturday, but I do expect that there will be some sunshine to break through the clouds, mainly in the afternoon. The upper level low pressure system should take all the rain east of the area, across the Carolinas. I expect that the race will be dry from start to finish. I do have to mention that the GFS model continues to show a high chance of rain on Saturday. Other models show a low chance. In my experience, the GFS tends to produce too much rain in this type of weather pattern, so I'm leaning toward the drier models. I think there will be too much dry air moving in and not enough lift in the atmosphere to produce measurable rainfall. Temperatures will continue to be a little cool, with highs in the upper 60s, and temperatures by the end of the race around 60.

We'll have our radar link ready to go at the top of the website later today.

By Doug Schneider

COTA and VIR are two really good tracks to verify forecasts because there is an airport with a reliable weather sensor within ten miles of both tracks. So here's a look back at how I did with my forecasts for Lone Star Le Mans and Trans Am at VIR.

Lone Star Le Mans was not a difficult forecast as I was confident that most of the event would stay dry, with the exception of Wednesday. Temperatures were clearly the main concern, with highs each day reaching into the lower to mid 90s. There was a shower that grazed the track on Wednesday, and 0.01 inches of rain was recorded at the airport that day, verifying my 20% rain chance. My forecast high temperatures were never off by more than two degrees. 

Trans Am had a very wet weekend at VIR. I'm pretty sure every session was affected by rain or at least a wet track. My initial forecast called for a chance of rain on Thursday, Friday, and Saturday, but I did not have it lasting into Sunday. My next forecast update corrected that, with rain chances rising to 70% Thursday night through Saturday, then up to 100% on my next update. This was the period when the greatest amount of rain fell. Light rain continued into Sunday, and a light mist or drizzle was over the track for the race start on Sunday afternoon. My forecast temperatures verified pretty well each day and night. What I didn't forecast well (and it doesn't show up in the chart) is rainfall amounts. In my posts, I had mentioned 0.5 to 1.5 inches with my 9/23 forecast, then 1 to 2 inches with my 9/24 forecast. Both of these forecasts were actually on the higher side of what the models were predicting. It turned out that 4.74 inches of rain was recorded through the event at the Danville airport!

By Doug Schneider

The main change to the forecast today has been for a slower low pressure system through midweek, which will extend the change of rain into Thursday. 

Wednesday will have a good chance of rain showers all day, but it will be the warmest day of the event, with highs in the upper 70s. On Thursday the cold front at the surface will have moved through, bringing cooler temperatures. However the upper level trough is slow to exit, and will be over Georgia through the day. This will result in some scattered showers around the track all day. The trough is expected to slowly move away, taking most of the deep moisture with it, so I don't expect that the showers will last into Friday at this time. If the models continue to show a slower system, I may need to add a chance of rain into Friday. 

Race day continues to look really nice as high pressure builds over the area. Mostly sunny skies and highs in the lower 70s can be expected. Temperatures by the end of the race will drop to around 60, so bring a jacket. 

By Doug Schneider

I'm happy to report that (so far!) the weather looks great for Petit Le Mans next weekend at Road Atlanta.

A cold front and upper level trough of low pressure will be crossing the southeast on Wednesday. The bulk of the rain associated with this system will likely come on Tuesday and Tuesday night, but there is a chance of some showers lingering into Wednesday. The system will exit Wednesday night, and as high pressure builds in, cooler and drier air will be sliding into northeast Georgia from the northeast. This should make for comfortable daytime temperatures and low humidity Thursday through Saturday. Highs will be in the lower to 70s, and morning lows may be a little on the cool side, dropping into the lower to mid 50s each morning. 

The latest run of the GFS model develops a low pressure system over the Plains and moves it into Tennessee by Sunday morning. If this occurs, there could be some rain on Sunday as teams and campers leave the track. But it does not appear likely to have an impact on the racing, unless later model runs show it moving faster. 

Stay tuned for updates through the week by following our Twitter feeds and Facebook page.