Airlines will escape having to pay flight delay compensation - the delay must be for at least three hours - if they can prove the delay was down to an extraordinary circumstance. If it was down to an air traffic management decision such as the suspension of flights due to thunderstorms, is that legally due to an extraordinary circumstance?
In Daniel Blanche v Easy Jet Airline Co Ltd  EWCA Civ 69, the airline maintained that thunderstorms did amount to an extraordinary circumstance. The passenger who was held up for five hours 42 minutes argued that it was not an extraordinary circumstance and that regard should be had to the underlying reason for the delay. There was nothing exceptional about thunderstorms!
Last Wednesday 06 February 2019, the Court of Appeal ruled that the airline was right and the passenger was wrong. The air traffic management decision amounted to an extraordinary circumstance so that the claim had to fail.
So whatever the underlying cause of the delay in your case, if air traffic control has prevented the flight from departing, I'm afraid you've had it.