Indeed I can't see you getting anywhere with compensation given the fairly obviously poor weather conditions at the time (and at both airports). However to answer the specific question, once you choose one option such as "Expenses incurred" and go a little further down with the questions, there should then be a new option to select another claim for the same flight, and there you can select "The compensation..." And just to add complexity, there is some logic in claiming expenses straight up since they can be paid quite quickly, and leaving compensation for a separate claim a few hours later - that will take longer to process.