Always better to go by actuals rather than forecasts when operating to Cork.
The flight crew get their MET briefing well before departure which may be 90 minutes or more before their scheduled arrival time at their destination airport.
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They are more interested on what weather is forecast for when they are scheduled to arrive.
Once they are getting close to their destination is the actual current weather of concern.
I think Ryanair acted too hastily in switching their morning departures to Shannon
They made a strategic decision to have their initial departures in a place where they were confident that they could leave on schedule.
This meant a slight hit initially to their operations but as the day progressed all other sectors could be carried out.