The slow-moving low pressure trough that has brought clouds and rain the past few days will continue to linger across northern France through Friday. This will keep a good chance of showers in the forecast, particularly in the afternoon. A thunderstorm can't be entirely ruled out either. Rain amounts around a tenth of an inch are likely, but if a heavier shower or storm moves over the track, a quarter inch of rain may be possible.
By Friday night, the trough should be exiting the area to the east, and high pressure will start to build in from the west. A few light showers may be around Le Mans Saturday morning, but I'm still expecting that they will be gone by the time the race starts at 3 pm local time (9 am EDT). With high pressure continuing to build over France, I expect that the race will remain dry for all 24 hours of racing.