Customers who have booked to fly to and from parts of the UK today could face disruptions due to poor weather conditions.
This will affect passengers at London Gatwick airport and the airline apologised for the delays that are outside its control.
Ryanair said there are "potential disruptions" because of fog and customers will be contacted if this affects their flights.
It said today: "Affected passengers will be notified and any passengers travelling to/from London Gatwick on Friday 17 May should check their Ryanair app for the latest updates on their flight.
Holidaymakers should check if travelling today
PA
"We regret any inconvenience caused to passengers by the weather conditions that are outside of Ryanair's control and affect all airlines operating to/from London Gatwick on Friday 17 May."
The airline advised customers to regularly check the app for updates and it said it would minimise disruptions where possible.
Passengers can sometimes be entitled to compensation when travel is disrupted or cancelled. This depends on the length and reason of the delays.
What to do if your Ryanair flight is delayed?
Passengers could receive vouchers, accommodation or compensation depending on the nature of their delay.
The airline states: "If your flight is expected to be delayed for two hours or more (for flights up to 1,500km) or three hours or more (for intra-EU flights over 1,500km and other flights between 1,500km and 3,500km) you will receive assistance at the airport, including meal coupons.
"Flights can be cancelled for reasons beyond our control, for example, ATC strike, adverse weather conditions, medical emergencies, etc.
"If your delay extends to the next day, we will oftentimes provide hotel accommodation and transportation between the airport and the accommodation."
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This affects Britons travelling to and from London Gatwick
PAHolidaymakers can also request to be rerouted, take the original flight at the new departure time or change to another flight.
For longer delays, you can also request a refund although the airline warned many of these applications are not successful.
It added: "For delays of five hours or more, if you choose not to travel, you can request a refund here, however, please bear in mind that most refund applications are unsuccessful due to situations that are outside of Ryanair’s control meaning we are not obliged to pay you a refund."