No compensation. Weather is an extraordinary circumstance.
Check your flightBad weather is the clearest example of what the regulation calls an extraordinary circumstance. Fog, snow, storms, and lightning are outside the airline's control, so when weather genuinely causes your delay or cancellation, no compensation is due. This is the one excuse that reliably works.
What weather does not cancel is your right to care. From two hours of delay onwards the airline still owes you meals, drinks, two phone calls, and a hotel with transfers if you are stuck overnight. Airlines routinely fail to provide this during weather disruption, when they are busiest. Buy your own meal, keep the receipt, and claim it back.
The part worth checking is whether weather was really the cause. Airlines sometimes cite weather for a delay that was actually caused by the aircraft arriving late from a previous rotation, or by a crew running out of legal hours. If the weather was hours earlier, or other airlines were departing normally at the same time, ask the airline in writing to state the specific cause. They have to justify it.
Compensation is a flat amount set by distance, not by ticket price: €250 up to 1,500 km, €400 for longer flights inside the EU and for 1,500–3,500 km, and €600 beyond 3,500 km. The UK equivalents are £220, £350 and £520.
Distance is measured in a straight line from your original departure airport to your final destination, which on a connecting itinerary often lands you in a higher band than you would expect.
Duty of care is separate from compensation and does not depend on the cause. Once you are delayed two hours or more the airline owes you meals and drinks, two phone calls, and a hotel plus transfers if you are stuck overnight. This applies in bad weather, during ATC strikes, and in every other situation where no compensation is payable.
Airlines frequently provide none of this during major disruption. Buy your own, keep every receipt, and claim the cost back afterwards.
Work out what you are owed