By: Stephen McCoy

There have been a few changes to the temperatures for the weekend, but overall the forecast for Indianapolis Motor Speedway is still fairly consistent to the initial forecast from Monday. There is a slight chance for isolated showers on Friday, however rainfall rate for the day is expected in the hundredths of an inch, if any occurs.

The synoptic setup for the rest of the forecast period remains the same: a cold front passed through today, which will bring west to northwesterly winds to the region for tomorrow, resulting in cooler overall temperatures. A low pressure surface trough will approach central Indiana on Thursday from the north, bringing a chance for scattered showers in the afternoon. Rainfall totals are expected under a tenth of an inch, but still could disrupt some of the scheduled on track sessions. Behind the trough, high pressure will build in, causing surface winds largely from the north to northwest, continuing to cool temperatures with a morning low in the mid 40's °F and a high in the mid 50's °F.

The area of high pressure is anticipated to move over or close to the Indianapolis region, resulting in calm and variable winds during Saturday morning, with winds then shifting to the south to southwest in the afternoon as the system continues eastward. Saturday night, a warm front extending from a low pressure system to the west will pass through the area, causing Sunday's low temperatures to remain relatively unchanged from the previous day's high. Southwesterly winds behind the warm front and ahead of the pairing cold front will allow temperatures to warm a few degrees before cooling again as the cold front passes through. Both mentioned fronts could bring a chance for precipitation on Sunday, especially in the morning, however rainfall totals will be largely determined by the location of the surface low's center.

By: Stephen McCoy

Cool, early-fall conditions are expected for this weekend's races at Indianapolis Motor Speedway, with chances for precipitation present at the beginning and end of the forecast period.

On Wednesday, a surface low pressure system will pass north of the Great Lakes as it tracks eastward towards the Atlantic Ocean. A trailing cold front will move through Indiana during this time period, setting up cooler temperatures for the region in the following days. West to northwesterly winds overnight Wednesday and into Thursday will result in morning low temperatures in the upper 40's °F and a high in the low 60's °F as the winds continue through the day. Behind the front, there is the possibility of a surface trough extending westward through the Great Lakes region from the aforementioned surface low and moving southward into Indiana during the day. The movement of the trough could bring a chance for scattered showers to the Indianapolis region, especially during the afternoon and may impact the various on-track sessions during this time.

As the surface low continues towards the east coast, high pressure is expected to slowly build into the region over the first part of the weekend. With the center of the surface high to the west, winds on Friday will be largely from the north to northwest, accompanied by partly to mostly cloudy conditions in the low to mid levels for much of the day. The cooler temperatures will continue with a low similar to Thursday and a high in the mid 50's °F. The surface high is anticipated to move over the central Midwest Friday night into Saturday, resulting in calm and variable winds for most of the early part of the day before shifting to the south as the high moves eastward. The lack of wind movement will extend to the low levels of the atmosphere, causing mostly cloudy to overcast conditions; temperatures will be similar to Friday.

Leading up to Sunday, an upper level shortwave trough will allow a low pressure system to develop at the surface over the northern Plains late Friday evening. Due to the trough's orientation, the surface low is expected to track southeastward, centering itself over Illinois on Sunday. Current model output disputes the exact location of the low, but general consensus indicates the center of the system will be either to the west or southwest of Indiana. As a result, a warm front will likely extend from the low somewhere over central Indiana; model output shows a disparity in the low temperature for Sunday as a result of the front, with a range of 10 °F in the most recent runs. In any case, the system is expected to bring a chance for precipitation and overcast skies through much of the day.

By Doug Schneider

Rain showers will start to spread into the Le Mans area beginning tonight. Periods of showers are likely to continue through Saturday as a low pressure system sits over the Bay of Biscay. The most likely period for showers on Saturday will be in the afternoon and evening, during the opening hours of the race. There could be around a quarter of an inch (around 6 mm) of rain that falls on Saturday. 

Saturday night should have a lower chance of showers in the area. Coverage will be more scattered, and showers will be lighter. The threat of thunderstorms will also diminish. Scattered showers will continue around northern France through Sunday, and there may be some breaks in the clouds that allow some sun to briefly shine through. 

I will be travelling on vacation with family tomorrow, so I won't be able to post radar updates as I usually do. I recommend this site to monitor radar - https://www.meteo60.fr/radars-precipitations-pluie-france.php

By Doug Schneider

Quite a bit of rain has fallen today at COTA, with just over a half inch of rain recorded at the Austin airport a few miles northwest of the track as of 4 pm CDT. The good news is that the rest of the event should be rain-free, with comfortable temperatures and plenty of sunshine.

The upper level low pressure system that brought rain to the area today will be tracking to the east, pushing rain off the Texas coast on Friday. With dry air expected to build in through the day, clouds will be decreasing from mostly cloudy in the morning to mostly sunny in the afternoon. 

The weekend weather continues to look great, with sunny skies Saturday and Sunday, with a northeast wind providing comfortable temperatures and humidity levels.

​There is one thing to note that I don't think will impact the racing, but could be a factor for Sunday night and Monday - A tropical system is expected to develop off the Texas coast over the weekend, and may start to drift to the west late Sunday. Rain may begin to spread back into COTA on Sunday night, but well after the racing has been completed.

By Doug Schneider

Not much has changed in the forecast for Le Mans with the latest data. Some things have come into better focus, such as the timing of the best chance of rain and potential rainfall amounts. 

High pressure over the British Isles will keep conditions dry and mild at Le Mans on Thursday, with mostly sunny skies. Clouds will start to increase a little on Friday as the high pressure system moves east and a low pressure system off the northwest coast of Spain approaches. As this low moves into the Bay of Biscay, it will start to bring a chance of rain into northern France, beginning Friday night. There is good agreement between the models that the center of the low will be just off the west coast of France on Saturday, sitting nearly stationary through the day. Shower and thunderstorms will be numerous across eastern and northern France all day, but the most likely time for showers to occur at the track will be in the late afternoon and evening - near the start time of the race. The rain could be briefly heavy if a storm moves directly over the track, with a quarter to a half inch of rain possible (6-12 mm). There could be a possibility of a caution period or a stoppage if the heavy rain and lightning occurs. 

The threat of showers will drop Saturday night, but it won't completely go away. There may be some scattered showers lingering around overnight and into Sunday morning. The chance of rain on Sunday looks lower than Saturday as the low pressure system is expected to weaken and drift southeast. Any showers on Sunday should be lighter as well, so the impact on the racing is expected to be less.