Weather Averages in Houston
Houston’s climate is classified as humid subtropical (Cfa in the Köppen climate classification system), typical of the Southern United States. The city experiences hot, long, and humid summers, and mild winters. While not located in Tornado Alley, like much of northern Texas, spring supercell thunderstorms sometimes bring tornadoes to the area.
Prevailing winds are from the south and southeast during most of the year, which bring heat and moisture from the nearby Gulf of Mexico and Galveston Bay.
During the summer, temperatures in Houston commonly reach over 90 °F (32 °C). The city reaches or surpasses this temperature on an average of 106.5 days per year, including a majority of days from June to September; additionally, an average of 4.6 days per year exceed 100 °F (38 °C). Houston’s characteristic subtropical humidity often results in a higher apparent temperature, and summer mornings average over 90% relative humidity. Air conditioning is ubiquitous in Houston; in 1981, annual spending on electricity for interior cooling exceeded $600 million (equivalent to $1.65 billion in 2018), and by the late 1990s, approximately 90% of Houston homes featured air conditioning systems. The record highest temperature recorded in Houston is 109 °F (43 °C) at Bush Intercontinental Airport, during September 4, 2000, and again on August 28, 2011.
Houston has mild winters. In January, the normal mean temperature at George Bush Intercontinental Airport is 53.1 °F (12 °C), with an average of 13 days per year with a low at or below 32 °F (0 °C). Twenty-first-century snow events in Houston include a storm on December 24, 2004, which saw 1 inch (3 cm) of snow accumulate in parts of the metro area, and an event on December 7, 2017, which precipitated 0.7 inches (2 cm) of snowfall. Snowfalls of at least 1.0 inch (2.5 cm) on both December 10, 2008, and December 4, 2009, marked the first time measurable snowfall had occurred in two consecutive years in the city’s recorded history. Overall, Houston has seen measurable snowfall 38 times between 1895 and 2018. On February 14 and 15, 1895, Houston received 20 inches (51 cm) of snow, its largest snowfall from one storm on record. The coldest temperature officially recorded in Houston was 5 °F (−15 °C) on January 18, 1930.
Houston generally receives ample rainfall, averaging about 49.8 in (1,260 mm) annually based on records between 1981 and 2010. Many parts of the city have a high risk of localized flooding due to flat topography, ubiquitous low-permeability clay-silt prairie soils, and inadequate infrastructure. During the mid-2010s, Greater Houston experienced consecutive major flood events in 2015 (“Memorial Day”), 2016 (“Tax Day”), and 2017 (Hurricane Harvey). Overall, there have been more casualties and property loss from floods in Houston than in any other locality in the United States.
Houston has excessive ozone levels and is routinely ranked among the most ozone-polluted cities in the United States. Ground-level ozone, or smog, is Houston’s predominant air pollution problem, with the American Lung Association rating the metropolitan area’s ozone level twelfth on the “Most Polluted Cities by Ozone” in 2017, after major cities such as Los Angeles, Phoenix, New York City and Denver. The industries located along the ship channel are a major cause of the city’s air pollution. The rankings are in terms of peak-based standards, focusing strictly on the worst days of the year; the average ozone levels in Houston are lower than what is seen in most other areas of the country, as dominant winds ensure clean, marine air from the Gulf.