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The Climate of Houston is classified as humid subtropical. Houston's warmest month (on average) is July at 84.5 °F (29.2 °C), and the coldest month being January at 54.0 °F (12.2 °C). The average yearly precipitation level is 54.0 inches (1,370 mm). Houston has occasional severe weather, mostly in the form of flooding. Spring supercell thunderstorms sometimes bring tornadoes to the area. Houston may sometime experience tropical cyclones during the hurricane season, which can bring significant damage to the city. The last to hit was Hurricane Ike in 2008.

Seasonal observation

Summer

The summer months in Houston are hot and humid, with occasional afternoon thunderstorms. The average daily high temperature peaks at 94 °F (34 °C) at the end of July,^[2] with an average of 99 days per year above 90 °F (32 °C).^[3] The average relative humidity ranges from over 90 percent in the morning to around 60 percent in the afternoon.^[4] The temperatures in the summer in Houston are very similar to average temperatures seen in tropical climates, such as in the Philippines and Central America.^[5] These values of relative humidity results in a heat index higher than the actual temperature.^[6] The hottest temperature ever recorded in Houston was 109 °F (43 °C) on September 4, 2000.^[7] Heat stroke can strike people who stay out of doors for long periods of time during the summer.^[8] Houston's heat and humidity made air-conditioning an essential element in Houston's early survival, and it continues to be important in day-to-day life.^[9] Air conditioning is considered the stimulus for the growth of Houston in 1950 when it became the most air-conditioned city in the world.^[10] Tropical cyclones can move into the area anytime during the summer months, bringing heavy rainfall.^[11]

Autumn

Autumn in Houston is fairly mild, with temperatures averaging near 79 °F (26 °C) during the day and 52 °F (11 °C) at night. ^[12] Cold fronts which move through the region during the fall can bring heavy, flooding rains, with floods most frequent throughout October and November.^[13] Tropical hurricanes move into the area from both the Gulf of Mexico and the eastern Pacific ocean through October. Since 1851, the latest a tropical hurricane has impacted Texas from the Gulf of Mexico, was Hurricane Juan (1985), on October 28 of that year.^[14]

Winter

Winters in Houston are mild and fairly temperate. While the average high in January, the coldest month, is 61 °F (16 °C), Houston sees an average of 18 days per year of 32 °F (0 °C) temperatures or less.^[15] The coldest temperature ever recorded in Houston was 5 °F (−15 °C) on January 23, 1930.

Throughout December, strong southward-moving cold fronts, called "blue northers," ^[16] batter the city with cold rain, low wind chills, freezing rain, and sometimes frozen precipitation. Early January is the coldest time of the year, with temperatures moderating by February.

Snow and ice

December 24th Snowstorm, shown on satellite.

Snow is unusual in Houston, with an event occurring nearly every 4 years. Snow has fallen approximately 30 times since 1895,^[17] more recently on December 4, 2009.^[18] Freezing rain events, also known as ice storms, can be detrimental to local traffic, and can close schools and businesses. The most recent ice storms occurred in 1997 and 2007.

Spring

Spring comes with a very mild warm up from winter, lasting from March 20 through May. Temperatures stay fairly low, not usually warming up above 77 °F (25 °C). Often during spring, supercell thunderstorms can occur, ^[19] prompting Houston's 10-month long "growing season" to begin. Spring also sees the return of many types of insects, including butterflies and mosquitoes, to return to Houston's infamous warm climate.

Spring slowly diminishes the colder winter temperatures, yet freezing weather can still occur on some nights in late March.

Precipitation

Rainfall is the most common form of precipitation in Houston. The wettest month is May, with 5.6 inches (140 mm) of rain. The city receives 47.9 inches (1,220 mm) of rain in an average year. The most precipitation to fall in one year was 72.86 inches (1,851 mm) which occurred in 1900. Houston has received less than 20 inches (510 mm) of rain only once: 17.66 inches in 1917.^[20] Flash flood warnings are common all year, and due to the flat landscape, heavy rains can be a threat to the city.

Sleet, snow and ice are unusual, and sometimes never occur at all during the winter. Hail can accumulate, yet only in small quantities. Frozen precipitation does not survive the warmer temperatures.

Extreme weather

Houston has occasional severe weather, mostly in the form of flooding. The effects of tropical cyclone landfall can bring severe damage to the city and region.

Hurricanes & tropical storms

Because of Houston's close proximity to the Gulf of Mexico, the city has a significant chance of receiving hurricanes and tropical storms every hurricane season.

Houston's history of hurricanes stretches back to 1837, when the Racer's Storm passed just to the south of the town, raising water levels four feet.^[21] The Great Hurricane of 1900, which razed nearby Galveston, also passed over Houston, but the hurricane weakened to a tropical storm by the time it reached Houston.^[22] The periphery of Hurricane Carla affected the city in 1961, causing major damage to Houston. At the time of landfall, Carla was the most powerful tropical system to affect the Texas coast in over 40 years,^[23] and many would follow its destructive path. In 1983, the city experienced a direct hit in the form of Hurricane Alicia, causing one billion dollars damage to the city and striking during a down period in the city's economy.

The most destructive and costly natural disaster in city history was Tropical Storm Allison of 2001, ^[24] which dumped up to 37 inches (940 mm) of rain on parts of the city over a 5-day period. The storm completely overwhelmed the area's flood control system and caused $6.05 billion (2006 USD) damage. It is the only tropical storm in history to have its name retired.

Tropical Storm Erin made landfall on the Texas coast in August 2007, and struck Houston with strong rains. A total of 9 inches (230 mm) of rain fell at George Bush Intercontinental Airport on August 16, 2007, and many roads and neighborhoods were flooded. METRO halted its light rail and bus services in view of the effects. The storm did fatal damage to a Randall's grocery store in Clear Lake, where its roof collapsed, killing one and injuring another. Another three deaths were reported throughout the city, and the Houston Fire Department reported 72 rescue operations. A total of 4 deaths were caused by the storm.

Hurricane Ike made landfall near Galveston, Texas in September 2008. The roof of Reliant Stadium was damaged and several buildings in Downtown Houston had their windows blown out. Storm surge also affected areas around Galveston Bay. Hurricane Ike has left ninety percent of people in the Houston Area without power. ^[25]

Flooding

Flooding is a major threat all year in Houston, particularly in fall and winter. The marshland around Houston easily floods, due to its low elevation. In fall, strong cold fronts batter the city, and flooding regularly happens. Many bayous in the city are adjacent to low-lying sections of the city, posing a threat of overflow and flood damage to many homes and businesses. Additionally, many of the city's older suburbs have outdated sewer systems, which can't drain water in the event of flash flooding.

Tornadoes

Unlike much of Texas, Houston is not considered a part of Tornado Alley, but smaller tornadoes are common during severe weather. They are most likely to be found along frontal boundaries of an air mass during the spring months. The most common tornadoes in Houston measure F1 on the old Fujita scale, and cause light to moderate damage to well-constructed buildings. The strongest recorded tornado in Houston history was an F4 on November 21, 1992, part of a large outbreak of tornadoes. ^[26]

Winter storms

Since 1895, it has only snowed 33 times in Houston, about once every 3½ years on average. Until 2008 and 2009, it has never snowed two years in a row. In 2008, it snowed on December 10 and 24, in itself a rarity, with the first one setting a record for the earliest ever. This was quickly broken the following year by a major storm on December 4.^[27] The 2004 Christmas Eve snowstorm brought a never-before white Christmas to the region. (Despite these, most snow falls in January, the coldest month.) Average annual snowfall is nearly zero however, being less than the measurable amount of 0.1 inches (2.5 mm).

Environmental issues

Houston is well-known for its polluted environment. Harris County alone is home to 15 Environmental Protection Agency Superfund sites, more than any other area in Texas. The list contains numerous companies, streets and waterways that have been considered dangerous to humans.^[28]

Air pollution

Houston is well known for its oil and petrochemical industries, which are leading contributors to the city's economy. The industries located along the ship channel, ^[29] coupled with a growing population, has caused a considerable increase in air pollution for the city each year. Houston has excessive ozone levels and is ranked among the most ozone-polluted cities in the United States.^[30] Ground-level ozone, or smog, is Houston’s predominant air pollution problem. In 2000, Houston earned the title of "most polluted city in America" by its standards and was ordered by the federal government to clean up pollution by 2007. ^[31][32] A 2007 assessment found the following twelve air pollutants to be definite risks to health in Houston:^[33]

• ozone - respiratory and cardiovascular effects
• particulates less than 2.5 μm in diameter (PM_2.5) - respiratory and cardiopulmonary effects
• diesel particulate matter (DPM) - cancer
• 1,3-butadiene - cancer and reproductive effects
• hexavalent chromium - cancer
• benzene - cancer
• ethylene dibromide - cancer
• acrylonitrile - cancer
• formaldehyde - cancer and respiratory effects
• acrolein - respiratory effects
• chlorine - respiratory effects
• hexamethylene diisocyanate - pulmonary and respiratory effects

The State of Texas concluded that, since 2000, the Manchester area in eastern Houston had the highest annual averages of 1,3-Butadiene of any area in Texas.^[34]

Houston has introduced many programs since the 2000 federal order to reduce air pollution in the city. The most notable project was the METRORail light rail system constructed in 2004. The light rail system was designed to encourage Houstonians to utilize public transportation instead of their automobiles.

Water pollution

Houston has also seen recent improvements to the city's waterways. The banks of Buffalo Bayou have been cleaned of garbage and have been turned into jogging trails and parks. Since the mid-1990s, Houston has seen a great increase in wildlife along the bayou due to many successful cleaning attempts.^[35] The Port of Houston has not seen any major cleaning attempts and continues to be polluted from the local refineries and industries.

Notes

External links

• Weather Averages for Houston
• Comparison with month average and actual temps