[FReepaholic]

...The contrails go wildly screwy in a zig-zag fashion all over the sky in just a few minutes after launch...

That's caused by wind shear. The wind blows in different directions and different speeds at different altitudes.

They will hold a launch if the upper level winds are out of spec for that particular vehicle.

[The KG9 Kid]

"... That's caused by wind shear. The wind blows in different directions and different speeds at different altitudes."

Exactly. Thank you.