The Tropic of Cancer effectively divides the country into temperate and tropical zones. Land north of the twenty-fourth parallel experiences cooler temperatures during the winter months. South of the twenty-fourth parallel, temperatures are fairly constant year round and vary solely as a function of elevation. This gives Mexico one of the world's most diverse weather systems.
Areas south of the twenty-fourth parallel with elevations up to 1,000 m (3,281 ft) (the southern parts of both coastal plains as well as the Yucatán Peninsula), have a yearly median temperature between 24 to 28 °C (75.2 to 82.4 °F). Temperatures here remain high throughout the year, with only a 5 °C (9 °F) difference between winter and summer median temperatures. Both Mexican coasts, except for the south coast of the Bay of Campeche and northern Baja, are also vulnerable to serious hurricanes during the summer and fall. Although low-lying areas north of the twentieth-fourth parallel are hot and humid during the summer, they generally have lower yearly temperature averages (from 20 to 24 °C or 68 to 75.2 °F) because of more moderate conditions during the winter.
Many large cities in Mexico are located in the Valley of Mexico or in adjacent valleys with altitudes generally above 2,000 m (6,562 ft). This gives them a year-round temperate climate with yearly temperature averages (from 16 to 18 °C or 60.8 to 64.4 °F) and cool nighttime temperatures throughout the year.
Many parts of Mexico, particularly the north, have a dry climate with sporadic rainfall while parts of the tropical lowlands in the south average more than 2,000 mm (78.7 in) of annual precipitation. For example, many cities in the north like Monterrey, Hermosillo, and Mexicali experience temperatures of 40 °C (104 °F) or more in summer. In the Sonoran Desert temperatures reach 50 °C (122 °F) or more