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you don't notice them or they are not there? it's pretty easy to track most planes and know where they are at any time
https://flightaware.com/live/
you could watch the skies above your area to see if there are really are any suspicious patterns. That's how they busted the FBI surveilling protestors illegally with aircraft because all the data of the locations of airplanes is public.

I would be very interested to check that website because it really does feel like there were planes everywhere yesterday and not a single one today. Thanks for the link!

I was looking at if for a while, it's sort of relaxing to watch them change position gradually. There are a whole lot of people who want to fly to a whole lot of places.

Geeze, you're not kidding. That is a load of planes... though according to this, none in our area, just as the sky is telling me. It will be very interesting to see what the map says next time the sky is covered in lines.

also check the barometric pressure and temperature to see if that is a factor. Some of the variation could be to other whether events, like if there is a big storm on the east coast of the US I would expect to see fewer flights going west from France.