Is the flight to Portugal turbulent?
Usually only lightly. Portugal's southern great-circle route rides the calmer edge of the North Atlantic jet stream, so it often sees less clear-air turbulence than the northern routes to the UK and Ireland. Winter can still bring bumpy stretches near the jet.
When is the smoothest time to fly to Portugal?
May through September has the weakest jet stream and the calmest transatlantic air. Winter brings a stronger jet and occasional Atlantic storm systems near the Iberian coast, which can make the approach into Lisbon or Porto gusty.
Why is there turbulence over the Atlantic?
The North Atlantic jet stream — a fast river of air at cruise altitude — creates wind shear at its edges that can jolt an aircraft without warning (clear-air turbulence, or CAT). It is strongest in winter and on the eastbound US→Europe leg, which rides the jet. Pilots change altitude to find smoother air, but CAT is invisible on radar, so it is the main reason to keep your belt on.
Where should I sit on a flight to Portugal?
Over the wing, near the aircraft's center of gravity, gives the steadiest ride. Keep your seatbelt fastened even when the sign is off — clear-air turbulence over the Atlantic can appear suddenly. Overnight eastbound flights often cross the jet stream while you are sleeping, so belt over the blanket.