Click images to enlarge
Rain is spreading across northern France early this morning as a low pressure system is sitting over the region. It will move very little through today, so there will be periods of showers on and off all day long. Thunderstorms may be possible at times as well. I don't think the rain will be heavy enough to stop the practice and qualifying sessions, with a quarter to a half inch of rain expected (7 to 13 mm). However, if there is thunder in the area, then there could be some stoppages. That chance is fairly low, maybe 20 to 30%.
The low will begin a northward drift on Wednesday night. As it does so, the chance of rain will begin to decrease. The system will be located over England on Thursday, so there could still be some showers across northern France that may affect Le Mans. I put the chance of that happening at 40%. If there is a shower on Thursday, I expect that it will be fairly light and brief, with little impact on the action.
Friday is looking better as the low is expected to be north of Ireland, with high pressure over the Alps building in. This should provide a dry day with warmer temperatures in the lower 70s F or lower 20s C.
On Saturday a trough rotating around the low pressure system to the northwest will pass across northern France. This could bring a few showers to the Le Mans area. The chance of one at the track is low, just 20%, and if it does happen it should be short-lived and light with little to no impact on the race.
I expect that Sunday will be dry, although there are some models that show some light showers popping up during the day. I'm not ready to go with that yet, so I'm keeping my forecast dry. Hopefully that holds up as we get closer to the weekend.