I'll just throw this out there for you. My first Le Mans was 2012, since then I missed 2013, 2016, and will be missing this year.
Every year I have been the weather has been fantastic. If anything the weather has been too good (HOT) when I've visited (2014 and 2017 come to mind).
So, if you want a guarantee of good weather in the future just take up a collection for me to visit. This way if I tell my wife that my trip is paid for she can't say no!