As with all questions of this sort, the answer is,'it depends on the circumstances of the case'.
Generally, an airline is required to pay flight delay compensation to passengers who suffer a delay of 3 hours or more. The airline are able to refuse to pay the delay compensation where the reason for the flight delay was beyond their control. This may be due to a security alert or something more common such as bad weather.
However, a word of warning: do not simply accept the airline's excuse - make sure you check the excuse given with a company such as ours. Why?
Well, we have had situations where an airline has told us the plane was delayed due to bad weather but, when we have checked other flights from the departure and arrival airports, no other planes were delayed. If no other planes were delayed, how come 'the weather' affected this flight?
Quite often, we are also given the excuse that bad weather affected an earlier flight which had a knock on affect. This is a permitted excuse but only where it is the immediately preceding flight. If it was several flights previously or even several days previously then this is not an acceptable reason. We can check these details to make sure that any valid claim for flight delay compensation goes ahead and a passenger is not put off by a reason which is not permitted.
If your flight is delayed or cancelled due to snow on the ground or there is fog at the airport then you will have to accept it as just one of those things - an act of God. If however everything looks ok to you, there isn't any obvious bad weather, then make a claim for flight delay compensation, even if the airline says it is due to bad weather. We can check if this really is the case or not.