By Doug Schneider

An area of thunderstorms is over the Chicago area early this morning, tracking toward the south. While the storms with this system will be dissipating before reaching Indianapolis, a residual boundary from it may become a focus for additional thunderstorm development in central Indiana late this afternoon. There is not good model agreement about the risk of thunderstorms at the Speedway, but there is enough of a risk that the forecast update has added a 20% chance of thunderstorms. If thunderstorms do form, they are likely to hold off until after 4 pm. This could affect the TA3/TA4 qualifying. 

​Hot temperatures are still expected for Sunday, reaching into the mid 90s under mostly sunny skies. 

By: Stephen McCoy

Lots of clouds for raceday at the 24 Hours of Le Mans. Temperatures for the start of the race will be consistent with previous forecasts, being in the upper 60s F, or around 20 C. A surface low pressure system is expected north of the British Isles and will move eastward through the forecast period. A cold front extending into northern France will move through the region during this time, and is the reason for some stronger winds at the start of the race. The front will move out of the region around midnight weakening winds through the night and morning on Sunday. Temperatures at the end of the race will be similar to those at the start.

Below is the astronomical information for the race from timeanddate.com

By Doug Schneider

I've made a few changes to the forecast for Trans Am at IMS with today's update, but the general weather pattern isn't significantly different from what I was seeing on Monday. A large high pressure ridge building over the region is expected to provide dry and hot conditions through the weekend.

The slight chance of rain that was forecast on Friday is now gone, as it looks like any thunderstorm activity on Friday will stay to the west and north of the Speedway during the day. 

Low level moisture will be increasing on Saturday, which means more instability, but the building high pressure ridge in the mid and upper levels will suppress convection over central Indiana. There will probably be some thunderstorms in northern Indiana that will track into western Ohio, but it is not expected to reach the Speedway. There is a little uncertainty about this, but I feel confident enough to keep showers out of the forecast for Saturday. With the ridge getting stronger, temperatures will be getting warmer, with a high in the lower 90s. 

Heat and humidity will continue to slowly rise for Sunday as the ridge aloft will continue to strengthen. Sunscreen and plenty of water will be needed if you're going to be at the Speedway this weekend. 

By: Stephen McCoy

As I mentioned in the previous forecast discussion, a strong surface low pressure system is expected to move through northern Europe, between Scotland and Iceland. As the system tracks eastward, a cold front will extend south from the system, bringing rain and strong winds to Ireland and the United Kingdom Thursday morning. As it progresses during the day, the front will extend to northern France causing some breezy conditions with some stronger wind gusts possible. Once the front exits the region, westerly winds are expected in the lower and upper levels of the atmosphere, in addition to the surface. These winds will bring moisture off the north Atlantic and bring a chance of precipitation into the area during the evening and into Thursday night; there is a possibility that passing showers could impact the qualifying sessions on Thursday.

As a result of showers overnight, some fog is possible in the early morning until sunrise on Friday. Overcast conditions are likely to start the day, but as the day progresses expect much of the cloud cover to break up. With little motion at the surface and lower levels, look for light winds out of the north and northwest.

For Saturday, a low pressure system will move towards Ireland and the United Kingdom from the North Atlantic Ocean during the morning hours. An upper level shortwave trough located over the surface low will help contribute to some slightly stronger winds at the surface during the day. However, as the day progresses, the shortwave trough will propagate east and winds in the upper level will shift towards the north. The surface low will likely weaken as it moves over the British Isles and as a result wind speed will likely weaken as well. With the combination of upper levels winds from the north to northwest, and lighter winds at the surface and lower levels, look for mostly cloudy skies for the majority of the day. Similar conditions are expected on Sunday, as upper level winds are likely to weaken from the shortwave trough continuing its track eastward.

By: Stephen McCoy

For Wednesday, winds in the upper and lower levels of the atmosphere and at the surface are expected out of the north. As the winds are vertically stacked through the atmosphere, some moderate wind gusts are likely. Partly cloudy skies should persist through the day as the winds will bring moisture off the North Atlantic Ocean and the English Channel.

A strong surface low pressure system located between Scotland and Iceland is expected to move towards the northeast past Scandinavia. A strong cold front will be associated with this system and will track over the United Kingdom and could extend into northern France in the early afternoon on Thursday. This will cause winds to shift from the north to the west to southwest, with some stronger gusts likely. With winds primarily out of the west from the North Atlantic Ocean in the upper and lower levels of the atmosphere, and lifting from the cold front, there is a chance of showers into the evening hours and overnight, likely impacting the 2nd and 3rd qualifying sessions for the 24 Hours.

Winds in the atmosphere will continue out of the west, though not as strong as on Thursday; surface winds will be variable through the day. A slight chance of showers is expected in the morning, as the mainly westerly flow will continue to bring moisture off the North Atlantic. As the day progresses, winds in the lower levels will shift towards the southwest. With the addition of daytime heating, precipitation chances will decrease and mostly cloudy skies will be expected for the remainder of the day.

For Saturday, conditions will start partly cloudy with variable winds at the surface and light winds from the west and southwest in the remainder of the atmosphere. As the day progresses, a shortwave trough in the upper atmosphere is expected to move through northern France; this will bring warmer, moist air into the area from the Bay of Biscay. With the addition of low level winds from the west to southwest, a slight chance of showers is expected in the afternoon to evening hours of the race. However, as the trough passes through the region overnight, winds in the upper levels will shift towards the north to northwest and as a result, precipitation chances will decrease into the morning on Sunday; mostly cloudy skies and light winds will persist throughout the remainder of the day.