Houston's climate is classified as humid subtropical (Cfa in Köppen climate classification system). Spring supercell thunderstorms sometimes bring tornadoes to the area. Prevailing winds are from the south and southwest during most of the year, bringing heat across the continent from the deserts of Mexico and moisture from the Gulf of Mexico.

During the summer months, it is common for the temperature to reach over 90 °F (34 °C), with an average of 99 days per year above 90 °F (32 °C). However, the humidity results in a heat index higher than the actual temperature. Summer mornings average over 90 percent relative humidity and approximately 60 percent in the afternoon. Winds are often light in the summer and offer little relief, except near the immediate coast, To cope with the heat, people use air conditioning in nearly every vehicle and building in the city; in fact, in 1980 Houston was described as the "most air-conditioned place on earth". Scattered afternoon thunderstorms are common in the summer. The hottest temperature ever recorded in Houston was 109 °F (43 °C) on September 4, 2000.

Winters in Houston are fairly temperate. The average high in January, the coldest month, is 63 °F (17 °C), while the average low is 45 °F (7 °C).Snowfall is generally rare. The last snowstorm to hit Houston was on December 24, 2004. The coldest temperature ever recorded in Houston was 5 °F (−15 °C) on January 23, 1940.

Houston has excessive ozone levels and is ranked among the most ozone-polluted cities in the United States. Ground-level ozone, or smog, is Houston’s predominate air pollution problem, with the American Lung Association rating the metropolitan area's ozone level as the 6th worst in the United States in 2006. The industries located along the ship channel are a major cause of the city's air pollution Downtown Houston is Houston's largest business district. In terms of office square footage, it is the seventh largest in the United States and has the fourth most concentrated skyline after New York City, Chicago, and Miami.

Downtown Houston contains the headquarters of many prominent companies. Many people do not know this, but there is an extensive network of pedestrian tunnels and skywalks connecting the buildings of the district. The tunnel system is home to many fast food restaurants, shops and services.

Most of the residential units in downtown are conversions of older buildings into modern and luxurious loft spaces. A number are located around the performance halls of the theatre district and near Main Street in the Historic District. Downtown will be adding another 600 plus units in the next couple of years with the developments of Marvey Finger's Park Tower (high rise) and the Houston Pavilions' two midrise loft towers.

A noticeable trend is that Houston is becoming more "downtown-centric". The baseball, basketball, and hockey teams have moved into downtown facilities. January 1, 2004 marked the opening of the "new" Main Street, a plaza with many eateries, bars and nightclubs, which brings many visitors to a newly renovated locale. To complete the scene, Main Street Square offers dancing fountains throughout the day and offers a dramatic scene. Along the Main Street corridor is the original Foley's department store which was transformed into Macy's on September 9.