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.