While turbulence is primarily determined by daily weather patterns rather than a specific month, the winter and early spring are statistically often cited as the least turbulent times for broad regions, provided there are no major winter storms. This is because "thermal turbulence"—caused by the sun heating the Earth's surface and creating rising pockets of warm air—is much less prevalent during the colder months. In contrast, the summer months often see more "bumpy" air due to heat-induced updrafts and localized thunderstorms. For the smoothest possible experience, the time of day actually matters more than the time of year; early morning or overnight flights are typically the calmest because the atmosphere has had time to cool and stabilize. Additionally, flying in the "red-eye" window often helps you avoid the chaotic convective activity that tends to peak in the late afternoon and early evening hours.