What you describe is very similar to wake turbulence in cruise. Aeroplanes criss cross paths all the time, with the required separation, but it takes time for these vortexes to lose their kinetic energy. And since they are, well, swirly, they can also travel around. So you might hit one without even seeing the aeroplane that made it.
TheRealGabossa t1_j6hs3x5 wrote
Reply to ELI5 what causes those random spots of turbulence on airplanes? by alekseyweyman
What you describe is very similar to wake turbulence in cruise. Aeroplanes criss cross paths all the time, with the required separation, but it takes time for these vortexes to lose their kinetic energy. And since they are, well, swirly, they can also travel around. So you might hit one without even seeing the aeroplane that made it.