The day will start with sunny skies, but clouds will be increasing through the afternoon. Temperatures will be quite pleasant, with highs in the lower 60s. In the closing hours of the race, clouds will be covering the entire sky. During this time, rain will be spreading across central and northern France, moving toward the northeast. The expected arrival time of the rain at the track is between 9 pm and 11 pm. The race ends at 8:30 pm, so it's going to be very close.
A link to radar for Belgium can be found here.