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The operative language in the EU air passenger rights regulation is:
An operating air carrier shall not be obliged to pay compensation in accordance with Article 7, if it can prove that the cancellation is caused by extraordinary circumstances which could not have been avoided even if all reasonable measures had been taken.
So in order to get out of paying compensation, the cause does not only have to be outside the airline's control -- it also has to be "extraordinary circumstances".
The European Court of Justice has taken a quite limited view of what counts as "extraordinary". Major (EyafjallajΓΆkull-scale) disruptions probably will be, but ordinary weather conditions that don't make the news (except very locally where they occur) probably won't. Weather trouble is viewed as an ordinary risk of doing business for airlines.
Thus, go ahead and claim compensation. If the airline refuses, you will then have to decide whether to take them to court to enforce your rights. There are several specialized legal agencies that will generally take these cases on a "you win or it's free" basis, in exchange for a cut of the compensation you get.