US Intelligence agencies had advance warning of the Iranian Missile attack it appears.
Reports suggest intercepts of "chatter" inside Iraq and Iran gave notice of the coming attack.
That comes as no great surprise considering today's technology and capabilities it provides in certain forms of intel gathering.
Also....no doubt there are Humint Sources available to the various Western Powers that could also be providing useful information.
I wonder if they are reading the posts here at pprune.....to see what the strategic experts among us are saying?