By Doug Schneider - @Race4caster

I'm putting out an update earlier than planned today because the models have shifted the chance of rain into Friday for Mid-Ohio today. The cold front that will bring numerous showers and thunderstorms on Thursday is still expected to move across the area on Thursday night, but the upper level trough will lag behind it, and keep a chance of showers into Friday. With the models showing the upper trough over Ohio on Friday, this will create some instability that will generate scattered showers. The showers could affect the track at any time of the day. At this time, the showers should be light, with perhaps at tenth of an inch of rain expected. 

The rest of the weekend still looks great, with pleasant temperatures in the 70s and lots of sunshine. Saturday will be breezy behind the departing low pressure system, with gusts around 20 mph at times.

By Doug Schneider - @Race4caster

The weather looks great at Mid-Ohio this weekend for IndyCar, MRTI, and Pirelli World Challenge racing. While the practice day on Thursday will likely have showers and storms, the rest of the event is expected to stay dry with comfortable temperatures and humidity levels.

A cold front will be approaching Ohio from the northwest on Thursday, There is some uncertainty about the timing details of the storms ahead of the front, so at this point I can't be too specific about it, and there could be showers at any time of the day. The cold front will move through Thursday night, and all the rain will be out of the area by the time cars hit the track on Friday morning. 

Behind the cold front, high pressure will settle into the Great Lakes region while a low pressure system will be east of the Appalachians, and this pattern will remain nearly stationary through the weekend. This will provide a north to northeasterly flow across Ohio that will keep temperatures and humidity levels very comfortable. High temperatures each day will be between 75 and 80, with low temperatures around 60. There will be a steady northeast breeze of 10 to 15 mph each day. 

Unless there is a major change in what the models are showing, which I doubt, my next forecast update will likely be posted on Wednesday. 

By Scott Martin - ​@RaceWx4You

You know what... I think we may have mostly dry conditions throughout much of the morning and the early afternoon hours at Exhibition Place in Toronto for race day for the Honda Indy Toronto. Both of the trusty forecast models that I use for short range outlooks are in very close agreement on timing with an approaching front that will be bringing showers to the area.

The good news is that it would appear that the best chances of showers and a possible thunderstorm would be likely starting after the 3PM EST and last through the remainder of the late afternoon and into the evening hours. There will be rain that should be moving by to the north of the event during the morning hours that could bring a light shower, but that shouldn't last very long at all and only be an inconvenience for a few minutes.

When, and if, the rain starts falling during the late afternoon, amounts will be around 1/4 inch or less, so I do not think it will be a washout, and I don't think the rainfall will be intense enough to bring out a red flag during the race. There will be enough to warrant the use of the gray sidewall Firestone Racing rain tires. Afternoon high will be around 81 degrees, and winds will be out of the southwest at 5-15 MPH. 60% chance for rain after 3:00 PM.

Unfortunately, the closest NWS Radar site in Buffalo, NY, has had a major equipment failure, so the software that we use for our site will be unable to do radar. Therefore, I will have updates throughout the afternoon on my Twitter feed @RaceWx4You using RadarScope.

By Scott Martin - ​@RaceWx4You

I am having to apologize for not putting up a discussion until today for this week's Verizon Indycar Series event in Toronto. Active weather in Alabama has once again kept me pretty busy. Here is the forecast for The Honda Indy Toronto.

Friday looks to be a pretty OK days in Toronto. The trusty forecast models that I am using are in pretty close agreement that rain should not be a factor throughout much of the day at Exhibition Center. I can't entirely rule out a stray shower or two moving through in the afternoon hours, but the risk is rather low at this point. The Canadian weather bureau has a 40% chance of showers and storms, I'm thinking that it will be less than that (about 20%), especially during track activity times. So I'll say mostly cloudy skies with a small risk of an afternoon shower or storm. Afternoon high will be in the lower 70s.

On Saturday, weather will not be an issue at all. It will be a mainly sunny day in Toronto, and quite warm as well. Afternoon high will be up in the lower 80s. Only concern will be getting sunburn. Be sure to pack the shades, hats, and sunscreen.

Sunday is going to be an interesting day at Exhibition Place. Some of the race fans who follow us have been complaining about not having a wet race. Well, there is a decent chance that rain tires will be needed for The Honda Indy Toronto. Both the GFS and NAM-12k are in agreement about a line of rain pushing through at some point during the late morning through the early afternoon hours. Considering that one is showing that the line will be sort of broken in nature, that will keep the chances a little lower in my eyes. With that being said, it will be a cloudy day with a decent risk for showers during the late morning throughout the afternoon hours. The afternoon high will be back down into the mid 70s. I'm pretty close in my thinking for rain chances with the Canadian weather bureau... I'm going 50%, they are going 60%. Either way, if it rains, we're both correct.

I will have radar up and running, but since the race is in Canada, the closest radar is located in Buffalo, I may not have the best geographical information. I am searching for the latest place files for our radar software, so hopefully I can find some that will suffice.

By Doug Schneider - @Race4caster

Not much has changed in my thinking for the forecast for Nurburgring this weekend, but some of the finer details are coming into better focus.

The chance of rain in Friday is expected to be mainly in the late afternoon, probably moving into the area between 3 and 5 pm, with the bulk of it falling between 5 and 7 pm CEST. Rain amounts do not look particularly heavy, perhaps around a tenth of an inch, or between 2 and 3 mm. 

Saturday will have cloudy skies but the rain will be well east of the area by then. With very little sunshine, high temperatures will only be in the upper 60s or lower 20s C. 

Sunday looks like a very nice day, with partly cloudy skies and temperatures warming into the upper 70s (mid 20s C). The slight chance of rain that I had in the previous forecast is gone, as that chance of rain will hold off until Monday.

By Doug Schneider - @Race4caster

The opening day of on track action at Nurburgring will likely have some rain. A cold front will be moving across the area in the morning, but a high chance of rain will continue through the day as the upper level trough moves through. There is pretty good model agreement on this general pattern, so I have a high chance of rain at 70%. Rain amounts at this time appear to be between 0.15 and 0.3 inches, or between 4 and 8 mm.

The upper level trough will be east of the area by Saturday, and a weak ridge will build over the area, so I think it will be a dry day with a mix of sun and clouds.

Sunday is probably the biggest question mark in the forecast. The ridge will be weakening through the day, and a weak upper level disturbance is expected to be crossing England and the Netherlands. With weak features like this, the models usually have a harder time figuring out their location and timing. I don't have a lot of confidence on Sunday's forecast, so I have just a slight chance of rain forecast for now with low impact on the race. We'll see how this evolves over the next few days, so check back for updates and follow @Race4caster on Twitter. 

By Doug Schneider - @Race4caster

Here's a look at the radar and surface observations across Ontario this morning:

CTMP is located at the red dot northeast of Toronto. I've drawn the approximate position of a cold front with the blue line. There are showers across Michigan and Lake Huron this morning, but I'm not too concerned with these affecting the track - the storms in Michgan will pass south, and the shower over Lake Huron is dissipating. I do expect that as the cold front tracks into southern Ontario late this morning, additional showers and thunderstorms will develop. I expect that there will be scattered storms in the area around CTMP between 2 pm and 6 pm. The chance of one of them hitting the track is about 50%. I have lowered the chance of rain from the previous forecast, as the coverage of showers does not look as great as it did a couple days ago. The Prototype Challenge and WeatherTech practice sessions are the ones most likely to be affected. Rain amounts around a tenth of an inch can be expected if a shower or storm hits the track, with an additional tenth of an inch possible tonight.

The cold front will move through the area tonight, and I expect the rain to exit with it. In the previous forecast, there was a small chance of a shower lingering into Saturday morning as the upper level trough moved through, but the timing of that looks faster today, so I've removed that small rain chance from Saturday morning. It should be a really nice day to be at the track, with cool temperatures in the 70s, low humidity, and a breezy northwest wind.

Unfortunately, Sunday is moving in a wetter direction. Another cold front will be approaching the area, and since it looks to arrive sooner than previously projected by the models, I've had to raise the chance of rain. The 30% chance of rain in the forecast graphic is the chance of rain during the race, which will be held between 12:05 pm and 2:45 pm. There is a higher chance of rain after the race ends. I expect that any rain that might fall during the race will be light, so I have the impact ranked as Low. It could just be some sprinkles that barely even wet the track, like we saw at the end of the Watkins Glen race. Heavier rain may arrive in the late afternoon or evening hours. 

By Doug Schneider - @Race4caster

My confidence in how the weather will play out at CTMP this weekend is increasing in some ways, but decreasing in others. It still looks like Friday's practice sessions will be affected by rain and thunderstorms, but there should be little to no weather impact on the racing action on Saturday and Sunday.

The models continue to point toward Friday for the best chances of rain as a cold front will be approaching the area. Numerous showers and thunderstorms will move through southern Ontario with the front during the day, and rain amounts are expected to be between a quarter and a half inch. This could cause some of the sessions to be canceled, so I've ranked the impact at Moderate. But that will depend on the finer details of timing of storms, which is still uncertain.

The cold front will move east of the area Friday night, but a trough in the midlevels of the atmosphere will lag behind. There will still be a chance of showers until that trough moves away, which will happen on Saturday. I think it will just be a slight chance of rain, mainly Saturday morning, and any rain will be light. By the afternoon, clouds will be decreasing and sunshine will be increasing, although it will be breezy with a northwest wind between 10 and 20 mph. The northwest wind will usher cooler temperatures into the area, and highs will be in the mid 70s. 

Sunday is becoming more of a question mark, as the models have changed their tune a bit about the pattern. One model (ECMWF) brings a second cold front and upper level trough into Ontario on Sunday, and it shows rain in the area Sunday afternoon. Another model (GFS) shows a much weaker trough and a front that stays north of the track. I've added a mention of an isolated late day shower to Sunday to account for the possibility, but I'd only put the chance of rain at 10% right now. I don't have enough confidence make a big change to Sunday's forecast at this point, since a dry day seems most likely. Hopefully that won't change as we get closer to the weekend, but stay tuned.

By Doug Schneider  - @Race4caster

The IMSA teams don't get much of a break this week after Watkins Glen, and neither do I. While there is a good chance of seeing rain this weekend at CTMP, I expect that the impact on racing will be low. 

Friday's practice sessions have the best chance of seeing wet conditions. An upper level trough and a surface cold front will be approaching the area from the northwest, and with a little daytime heating, showers and thunderstorms should develop across much of Ontario during the day. The afternoon is probably going to have higher rain chances than the morning due to more instability, but timing is still too uncertain this far out to be confident about that. 

The cold front is expected to move across southern Ontario on Friday night, taking the bulk of the rain with it, and the models are in pretty good agreement about that. However, they differ on how fast the upper level trough moves through, and so I don't have a lot of confidence about what will happen on Saturday. I have a slight chance of rain mentioned on Saturday to account for the possibility of the slower scenario. Even if there is rain on Saturday, it will most likely be light and have little impact on the racing. It is possible that the trough could move through faster, taking the rain away on Friday night, and Saturday could stay dry. In either case, it does look like cooler temperatures will build in behind the front for Saturday, with highs in the mid 70s (lower 20s C). It will be a little breezy too, with a north wind at 10-15 mph. 

Sunday looks like a great day for racing. The models agree on high pressure building over the Great Lakes, and a dry north to northwest flow providing dry air aloft. I expect mostly sunny skies and highs in the upper 70s (mid 20s C). 

Follow along on all our social media feeds on the right sidebar to keep up with changes in the forecast through the week.

By Doug Schneider - @Race4caster

Today's weather at Watkins Glen will be much improved compared to yesterday, but there's still a small chance of a shower in the afternoon. The odds favor a dry race, but I can't rule out the possibility of a shower toward the end of the race.

Fog has been observed around the area, with visibility at the Elmira airport at a quarter mile at 6 am. Any fog at the track will be in the process of lifting around 8 am when the morning warm up session starts. If the fog is thick enough, it could delay the session. At the start of the race, it will be mostly sunny with a light southwest wind. Temperatures will warm to around 80 degrees by 2 pm. 

A broad upper level trough will be over the region today, and it will create just enough instability to spark some showers in the Finger Lakes region this afternoon. This is a simulation of what one model (HRRR) thinks the radar could look like this afternoon, from noon to 5 pm:

Sometimes this model develops too many showers in this type of situation, so I think the coverage of showers will be a little more sparse than what it is showing. I'd put the chance of a shower hitting the track today at about 20%, with the timing of possible showers between 2 pm and 5 pm. 

By Doug Schneider - @Race4caster

On and off rain showers will continue across the Finger Lakes region through the morning hours. Here's a look at the big picture radar (WGI is the red dot):

There is still quite a bit of rain across western Pennsylvania moving northeast that will affect Watkins Glen today. I expect that the main area of rain and thunderstorms will occur at the track between 8 am and noon. Around a quarter inch of rain is likely, and possibly up to a half inch. This could potentially impact Prototype Challenge Race 2, Porsche GT3 Cup Race 2, and WeatherTech qualifying.

There is also a Slight Risk of severe thunderstorms in the area. Here's the graphic from the Storm Prediction Center: 

Watkins Glen is on the western edge of the Slight Risk area. While there is a potential for storms to produce strong wind gusts, I think the chance of this happening at the track today is very low. The greater threat of severe weather will be east of Watkins Glen, where storms will have more time to develop in an unstable air mass this afternoon. Lightning will be a threat at the track today, so have a plan to seek shelter when thunder is heard. I do expect that most of the showers will exit in time for the CTSC race, which is scheduled to start at 2:25 pm. 

I don't have a new forecast graphic today, because my thinking for Sunday is pretty much unchanged from yesterday. It will be a partly cloudy day, with temperatures reaching to around 80 degrees in the afternoon. There is a slight chance of showers developing in the afternoon as an upper level trough will linger over the region. The timing for potential showers on Sunday appears to be after 2 pm. I'd put the chance of rain during the race at just 20%. A dry race continues to be the most likely scenario right now.

By Doug Schneider - @Race4caster

The rain managed to avoid Watkins Glen yesterday, passing to the north and to the south. That won't repeat today. Here's a look at the big picture radar this morning:

Movement of the rain in the image is toward the northeast (Watkins Glen is at the red dot). The first area of rain that is over western New York and northern Pennsylvania will produce some light rain at the track this morning, mainly between 8 and 10 am. Only a few hundredths of an inch can be expected from this initial round, and a period of dry conditions and partial sunshine can be expected behind it late in the morning and early in the afternoon.

A second area of rain is located over Ohio, associated with a disturbance in the mid and upper levels of the atmosphere. It is this disturbance that will bring numerous showers and storms to the track this afternoon, and it will be aided by increasing instability as temperatures warm up. The most likely time period for storms will be between noon and 5 pm, so the Prototype Challenge and Lamborghini Super Trofeo races may be impacted, with wet conditions or possibly delays. There is a slight risk of severe storms, capable of producing damaging winds and hail. While the chance of a severe storm is low, lightning and heavy rain will be the greater risks at the track today, and fans at the track need to stay aware of the weather and be prepared to seek shelter once thunder is heard. If you can hear thunder, you are close enough to be struck by lightning. 

Storms this afternoon will move east by sunset, and the overnight hours should mostly be dry. But the chance of rain will increase again on Saturday. I expect that there will be a greater impact on the racing, due to a better chance of heavier rain and strong or severe storms than today. A cold front will move across the area, and storms ahead of it are expected from the late morning into the early afternoon. Gusty winds, heavy rain, and lightning can be expected. Again, there is a slight risk that storms in the area will be severe, capable of producing damaging winds and large hail. All storms will produce lightning and heavy rainfall. If a storm passes directly over the track, a quick half inch of rain may fall.

It's a little hard to be specific on timing, but right now I think the window for the best chance of rain Saturday will be between 10 am and 4 pm. I would not be surprised if IMSA WeatherTech qualifying was cancelled. The start of the CTSC race will likely be impacted by wet conditions, or possibly delayed. 

The timing of this system is looking a little faster than before, and I'm confident that the front will be through the area Saturday evening. The storms associated with the front will be long gone by Sunday morning, however there will still be an upper level trough over the area, so I can't completely rule out the chance of an isolated shower on Sunday. It is most likely that the entire 6-hour race will stay dry. If there are showers in the area, they are most likely to occur in the mid to late afternoon when a little instability can develop, near the end or after the end of the race. 

Our radar link at the top of the page is up and running for Watkins Glen to help you stay aware of approaching storms. 

By Doug Schneider - @Race4caster

The general weather pattern hasn't changed much since my original forecast, but my confidence is increasing that there will be rain at the track on Thursday, Friday, and Saturday as a couple of low pressure systems track across the region. Sunday is actually looking pretty good, and will have the best weather of the event. The details of timing and rain amounts are still a bit uncertain, and the both of those factors will determine how much impact there will be on the racing. In any case, if you're headed to the track this weekend, you will definitely want to bring your wet weather gear along. It will come in handy at some point. 

On Thursday, moisture will begin to spread into the area from the south as a low pressure system tracks across Ontario. The question about Thursday is how quickly rain will move into the area. Over the past few days, most of the models have favored the afternoon and evening hours for rain, and this timing seems to be on track. Most of the rain may come after the practice sessions for the day are done, so I only have a low impact for Thursday even though the rain chance before sunset is high. Rain amounts around a tenth seem likely before sunset. More rain is expected after sunset, possibly another quarter of an inch.

Friday continues to be the least confident day for me as Watkins Glen will be between low pressure systems, and model agreement is poor. Although the atmosphere will be very moist, there isn't a strong mechanism in the atmosphere to produce lift for rain, and this is when the models tend to do poorly. At this time, I think there is about a 50/50 chance of seeing rain at some point in the day. With some sunshine possible at times, temperatures should warm up into the mid 80s with winds from the southwest at 10-15 mph. 

The second low pressure system will track across the Great Lakes and Ontario on Friday night and Saturday, with its trailing cold front moving through Saturday night. With the warm, moist air mass in place and lift provided by the approaching front, I expect numerous showers and thunderstorms around the track on Saturday. Timing of the best rain chances is tough to pinpoint this far out, as it looks like there could be storms at any time during the day. Rainfall amounts could be somewhere in the range of 0.25 to 0.75 inches, and the rain could be heavy at times. For this reason, I've ranked the impact on Saturday as moderate. I expect there will at least be some delays to the on track action, with some cancellations possible. 

The front will move east of Watkins Glen Saturday night, but the upper level trough will lag behind slightly, which is why I have a slight chance of rain mentioned Sunday morning. I don't think any rain on Sunday will have an impact on the race, as it will be light if it even happens at all. Clouds will be decreasing through the race, and it may be mostly sunny by the end, with temperatures getting close to 80 degrees. 

We'll have our radar link at the top of the page ready to go for Watkins Glen by Thursday. 

By Doug Schneider - @Race4caster

It appears that the weather pattern across upstate New York will be rather active later this week, which will result in at least a chance of rain each day for the Sahlen's Six Hours at Watkins Glen International. There are some uncertainties about the timing and amounts of rain, as there are some differences in the finer details between the models we use, but they do agree on the general pattern being a wet one. 

By Scott Martin - ​@RaceWx4You

First of all, I want to say a big "thank you" to you, the site regulars, for being patient on forecast updates. In my home state of Alabama, the weather has been quite active with the remnants of Tropical Storm Cindy moved onshore and now has moved off to the east coast. Rainfall amounts over the past 3 days have been incredible, with most in our state receiving over four inches, with some nearing the ten inch mark. We have also had our share of destruction, with an EF-2 tornado touching down just a few miles down the road from my location. Today I woke up relieved because I knew there would be no severe threat for me today, even with rain falling at this moment. Now let's get to the forecast.

The above image is the latest HRRR model run showing the simulated radar valid at 1PM. On this model run, this is when the most active weather will be going on across Wisconsin today. The good news is that most of the activity stays well to the north of Road America. The bad news is that there will be some scattered activity around the area. Now I do not believe that the coverage of rainfall will be as great as it shows in the model, but I think that a passing shower is possible at the track. Skies will be mostly cloudy throughout the day, and winds will be quite breezy out of the northwest at 10-15 MPH, gusting to 25 MPH at times. I'm only going with a 20% rain chance today, as the model shows much of the day being dry at the track.

There will be a line of showers and storms pushing through the area after 7PM, but I think most of the action will go south of the track. There will be a good chance of rain falling though, so campers may have to find some shelter for a little while. There may be some thunder, but nothing strong or severe is expected.

I'm going with an almost completely dry forecast for Sunday as of now. Looking at the latest model trend, there will be more showers and storms forming throughout the afternoon hours, but most, if not all, of the activity will stay west of the track until after 5-7PM tomorrow evening. Skies will be partly sunny, and winds will be out of the west-northwest at 10-15 MPH. I'm going with a 20% rain chance because I do believe it will stay dry at the track, but a stray shower is possible.

Radar is up and running on the website, so please feel free to take a look at anytime throughout the weekend. Have a great weekend!

By Scott Martin - ​@RaceWx4You

The weekend forecast for Road America at this point doesn't look too bad, but we may have to put up with a little wet stuff at some points throughout the event. Believe it or not, the tropical system that is affecting the Gulf Coast is messing with the forecast, so some of the details are not set in stone as of yet. I'll nail those down within the next day or two.

There is a surface boundary that is forecast to stall out over the Wisconsin/Illinois border, and this may bring showers and thunderstorms to the area on Thursday, especially during the afternoon hours. There is a possibility that the weather on Wednesday could make the storms form farther to the south on Thursday, we'll just have to wait and see on that part. By Friday, all of the shower activity will have moved out of the area, and the day is setting up to be nice and dry with mild temperatures.

We'll have a slightly active weather pattern setting back up over the area for Saturday as troughing starts to form and begins to move near the area. This will allow several waves to move through the area, but as of now, rain chances will be small and mainly during the afternoon hours. Same story on Sunday, but rain chances will be even smaller, and I wouldn't be surprised if I will be able to remove those rain chances out of the forecast within the next day or two.

Bottom line: We'll mention the chance of rain on both Saturday and Sunday, but more than likely it will stay dry at the track. I'll have a really good idea by Wednesday night on what the weather will hold for us at Road America.

By Doug Schneider - @Race4caster

Click images to enlarge

Perfect racing weather is expected from start to finish for the 24 Hours of Le Mans. There will barely even be a cloud in the sky. Temperatures will be pretty warm today, and a little warmer tomorrow. The forecast has played out pretty much as I expected since my first forecast last weekend, so there's not much to day other than enjoy the race!

​Here's the astronomical information for Le Mans today (from timeanddate.com):

By Doug Schneider - @Race4caster

Click images to enlarge

The weather continues to look great for the 24 Hours of Le Mans. Surface high pressure will be located near the English Channel Friday through Sunday, while a strong ridge in the mid and upper levels of the atmosphere will be across France. This ridge is trending a little stronger in the latest model runs, which is why I have bumped up the temperatures a few degrees for today's forecast update. With the strong ridge in place, there will be lots of sunshine and no chance of rain for the driver's parade on Friday and throughout race. 

I'll have a more detailed forecast of temperatures through the race on Saturday morning.

By Scott Martin - ​@RaceWx4You

Looking at the latest GFS model trend for this weekend, we'll have moisture in the Central Indiana area throughout each day, but I believe we may be able to squeeze at least two days of racing action without any interruption from Mother Nature. Even though I do have a small chance of rain for Friday, I believe we can make it throughout the day completely dry. The reason for the 20% chance is that models do not handle convective pop-up showers and storms well.

Just about the same can be said for Saturday but had to up the risk a little bit as precipitable water values will be higher, around 1.75 inches. There will be scattered shower and storm development, but I believe those will come later in the afternoon. Crossing my fingers that the on-track activity will be completed by the time those form.

More available moisture will be in the area on Sunday, with precipitable water values up around 2.00 inches. Showers and storms will be able to develop easier with the heating of the day, so there will be scattered to numerous showers around especially during the afternoon hours.

It is still early in the forecast game, but I'll be able to have a better look at what to expect when the higher resolution models come out this week. Radar will be up by Thursday on the site.

By Doug Schneider - @Race4caster

Click images to enlarge

There hasn't been a significant change in my thinking for the forecast for Le Mans, except for a shift in the timing of rain chances from Wednesday to Wednesday night/Thursday morning. The low pressure system that I mentioned in the last forecast post is trending a little slower, which will push the chance of rain more into Wednesday night. There's just a slight (20%) chance of the rain continuing into Thursday morning as the low exits to the east. The amount of rain continues to look very light, and perhaps less than before - just a few hundredths of an inch, or a millimeter or two. So no impacts are expected at the track. 

The rest of the week continues to look dry, sunny, and warm as high pressure builds over the region. It's going to be a great weekend to take in the Le Mans experience. Wish I could be there!

By Doug Schneider - @Race4caster

Click images to enlarge

I'm not sure you could ask for much better weather for Le Mans week than what I'm expecting this year. There is good model agreement in the general weather pattern, so my confidence in this forecast is fairly high, which means I don't expect bug changes to it as we go through the week.

Practice sessions begin on Wednesday, and that could be the only day that has a chance of rain. There is likely to be a low pressure system moving west to east across southern or central France that day. The position of the low will affect how much, if any, rain falls at the track on Wednesday. It may stay far enough south that no rain will fall, but I think there's enough of a chance to include a 30% probability of rain. It does appear that any rain will be light, so any impact on the practice session should be low. Amounts will likely be less than a tenth of an inch, or less than 2.5 mm.

The rest of the week looks dry as surface high pressure will be centered off the west coast of France, providing a north to northwest flow across the country. Thursday may be a little breezy as the high starts to build in behind the low, with a northwest wind at 10-15 mph (16-24 km/h). Sunny skies with a slight warming trend are expected through the rest of the week and into the weekend. Unless there's a major shift in the pattern shown by the models, it's going to be perfect racing weather through all 24 hours. 

Follow me on Twitter and our Racecast Weather social media feeds on the right for weather updates through the week.

By Doug Schneider

The festivities for the 24 Hours of Le Mans begin this Sunday with the traditional scrutineering ceremonies at the Place de la République in the town center of Le Mans. There's always a big crowd on hand, as it provides fans an opportunity to get up close to the cars and drivers in a relaxed setting.

The weather looks good for scrutineering this year. Sunday will have warm temperatures and plenty of sunshine, with highs in the upper 80s F and around 31 C. A cold front is expected to move across the area Sunday night, but with very little moisture to work with, the front is not expected to bring any rain. Even if there were some sprinkles, it would likely be overnight. Temperatures on Monday will be a little cooler behind the front, and winds will shift to the northwest. Early morning clouds will give way to plenty of sunshine by midday.

The long term outlook for the week leading up to the big race looks promising for nice weather. The models are in general agreement that a large high pressure ridge through the lower and mid levels of the atmosphere will be across western Europe through the week and into the race weekend. Here's a depiction of what the pattern is projected to look like near the start time of the race next Saturday from the ECWMF Ensemble Prediction System:

The colors represent heights at the 500 mb pressure level, so the ridge of orange colors over western Europe indicate a high pressure ridge through the midlevels of the atmosphere. The black lines are surface pressure, and we see the center of a high pressure area near Netherlands. This pattern will favor dry conditions and warm temperatures for Le Mans late in the week and the race weekend. Keep in mind that this is a forecast for 240 hours away, so things are likely to change somewhat as we get closer to the race. But so far, all signs point toward nice weather at Le Mans. 

I'll have a forecast graphic for Wednesday through Sunday posted on Sunday, so be sure to check back then.

By Doug Schneider

The weather still looks good overall for IndyCar's visit to Texas Motor Speedway this weekend, but I have added just a slight chance of a storm on Friday with today's forecast update.

In my post on Monday, I mentioned some uncertainty about the rain chances on Friday. That chance looks slightly higher today, due to a little more moisture and instability that could be present, and a weak upper level disturbance. But I still think that it is highly likely (around an 80% chance) that all racing activities will be held without any weather issues on Friday. Saturday continues to look dry, with temperatures during the race from the mid 80s at the start to lower 80s by the finish. There will be a south wind at 10 to 15 mph with gusts near 20 mph, which could create a tricky crosswind in turns 3 and 4.

By Doug Schneider

A fairly typical weather pattern for north Texas is expected this weekend as IndyCar moves to Texas Motor Speedway, which should mean dry conditions with warm temperatures for the end of the week.

On Friday there will be a southerly flow in the low levels, which will bring some moisture off the Gulf of Mexico. However, there will be a ridge in the mid and upper levels of the atmosphere, which should provide stable conditions over north Texas that will suppress thunderstorms. There will be a dryline developing over west Texas in the afternoon, but it does not appear that there will be a lot of storms developing along it, and if they do, they will stay well to the west of TMS. I'm not 100% confident that there won't be an isolated storm on Friday evening, but the chances of rain at the track appear too low to mention right now.

I'm more confident that Saturday will be dry, as the atmosphere looks like it will be drier and more stable than Friday. A dry northwesterly flow in the mid and upper levels will continue, and if storms are able to form on the dryline, they will stay well to the west. 

By Doug Schneider - @Race4caster

The forecast for Detroit this week has been a moving target, but the pattern is starting to come into better focus as we get closer to the weekend. There are still some uncertainties about the timing of rain chances at Belle Isle, but the latest data point toward a better weekend for racing than previously indicated.

Friday looks like a nice day at the track, with mostly sunny skies and highs in the mid 70s. A cold front will be pushing south toward Belle Isle on Friday, but it isn't expected to move across the area until Friday night. The front will have very little moisture to work with, so there may not be any rain with it when it moves through. 

High pressure will be building over the area on Saturday, and the front will be to the south of Detroit, across northern Ohio. Most of the day will be very nice, with mostly sunny skies and highs in the mid 70s. However, as a low pressure system approaches from the west, a southerly flow will develop, spreading greater moisture into the area and pushing the front back to the north. While I think the majority of the rain with this will come after Saturday's racing ends, there is some uncertainty about timing, so I have just a 20% chance of rain late in the day, but with very low impact on the IndyCar race at 3:30 pm. No impact is expected for the Trans Am and IMSA races that will be held earlier in the day.

Showers and thunderstorms are likely on Saturday night into Sunday morning as low pressure track east across Michigan, but the big question is, when will it end? There is a lot of uncertainty about this, but what I can say is that conditions should be improving through the day. The most likely sessions to be impacted by rain will be IndyCar qualifying and Trans Am Race 2. It is possible that there could be enough rain to cause some delays to these sessions, depending on how well water drains off the track.There will still be a chance of rain through the afternoon, but the chance will be lower than in the morning. I'd put the chance of rain in the morning at 60%, but closer to 40% in the afternoon. The Stadium Super Trucks and IndyCar Race 2 will probably have a wet track to deal with, but I don't think the conditions at that time will be bad enough to cause major delays or cancellations.

We'll have our live radar feed going through the weekend - just use the Radar link at the top of the website. I'm going on a beach vacation with my family this weekend, so my weather updates on Twitter will be limited, but Scott (@RaceWx4You) will help to keep you informed of the latest weather conditions at Belle Isle.

The forecast graphics for IMSA and Trans Am (Impact level differs based on the timing of races and expected rainfall):