During the height of Orlando's humid summer season, high temperatures are typically in the lower to mid 90s °F (32–36 °C), while low temperatures rarely fall below the mid 70s °F (23–26 °C). The average window for such temperatures is April 19 – October 11. The area's humidity acts as a buffer, usually preventing actual temperatures from exceeding , but also pushing the heat index to over . The city's highest recorded temperature is , set on September 8, 1921. During these months, strong afternoon thunderstorms occur almost daily. These storms are caused by air masses from the Gulf of Mexico and the Atlantic Ocean colliding over Central Florida. They are highlighted by spectacular lightning and can also bring heavy rain (sometimes several inches per hour) and powerful winds as well as rare damaging hail.