I seen something like this near the state line of Michigan and Indiana about 2 – 2 1/2 years ago while I was working one day (I was a delivery driver) and seen a small white plane fly across the sky a good while ahead of me. Behind it was this small thin white line (which is why I noticed it). I thought nothing of it until literally minutes later the thin line grew and grew and ultimately became these large white clouds, but they were in a straight line and followed the plane I saw. I grabbed my phone and took I believe 4-5 photos while I was driving and strangely the clouds got bigger and bigger in each shot I took until they became storm clouds. I drove right under them and they produced some of the heaviest rain fall I have ever seen. It took a matter of maybe 15-20 minutes for it all to happen until I passed under them. I still have the photos on my phone.