Climate of Houston
|Climate chart (explanation)|
The Climate of Houston is classified as humid subtropical. Houston's warmest month (on average) is July at 94.4 °F (34.7 °C), and the coldest month being January at 53.1 °F (11.7 °C). The average yearly precipitation level is 49.8 inches (1,260 mm). Houston has occasional severe weather, mostly in the form of flooding. Spring supercell thunderstorms sometimes bring tornadoes to the area. Houston sometimes experiences 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 
|Climate data for Houston (Intercontinental Airport), 1981–2010 normals,|
|Record high °F (°C)||87
|Average high °F (°C)||62.9
|Average low °F (°C)||43.2
|Record low °F (°C)||5
|Precipitation inches (mm)||3.38
|Avg. precipitation days (≥ 0.01 in)||9.6||9.2||8.8||6.8||8.0||10.6||9.1||8.3||8.0||7.9||8.2||9.5||104.1|
|Percent possible sunshine||45||50||54||58||62||68||70||68||66||64||52||51||59|
|Source #1: NOAA (Average percent sunshine through 2009) |
|Source #2: ThreadEx (records, 1889–last full calendar year)|
June through August in Houston is very hot and humid, often with scattered afternoon showers and thunderstorms. The average daily high temperature peaks at 100 °F (38 °C) at the end of July, with an average of 99 days per year above 90 °F (32 °C). The average relative humidity ranges from over 90 percent in the morning to around 60 percent in the afternoon. 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. The values of relative humidity results in a heat index higher than the actual temperature. The hottest temperature ever recorded in Houston was 109 °F (43 °C) on September 4, 2000 and tied on August 27, 2011. Heat stroke can strike people who stay out of doors for long periods of time during the summer so hydration is essential for outdoor work and recreational activity. 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. Most workers are relatively unaffected by the heat since they spend the hottest part of the day indoors in air conditioning. Air conditioning is considered the stimulus for the growth of Houston in 1950 when it became the most air-conditioned city in the world.
On June 5, 2011, the temperature reached 105 in Houston, making it the highest temperature ever recorded in June. And in exactly the same year, the temperature reached 100 in Houston on June 2, 2011, making it the earliest day in the season to ever reach the century mark.
Autumn in Houston is warm, with temperatures averaging in the upper 60s to lower 80s °F (20-28 °C) during the day and in the 50s to lower 60s °F (10-17 °C) at night. Cool fronts that move through the region during the fall can bring rain. Hurricanes can move into the area from the Gulf of Mexico bringing heavy rains and high winds. However, most years see little or no significant hurricane activity. Flooding is most frequent in October and November. Since 1985, the latest a hurricane has impacted Texas was Hurricane Ike (2008).
Winters in Houston are very mild and temperate. While the average high in January, the coldest month, is 62.9 °F (17.2 °C) and the low 43.2 °F (6.2 °C), Houston sees an average of 18 days per year of freezing temperatures. Cold fronts during the winter drop nighttime lows into the 30s, averaging out at 36°F (2.2°C) but usually above freezing. There usually is a period of about three weeks with what would be considered "winter" weather—temperatures in the low 30s to mid-40s. 'Hard freezes' are uncommon. The coldest temperature ever recorded in Houston was 5 °F (−15 °C) on January 23, 1930.
In December, southward-moving cold fronts  can bring cold rain, low wind chills, freezing rain, and rarely frozen precipitation. Early January is the coldest time of the year, with temperatures moderating slightly by February.
Snow and ice 
Snow is extremely unusual in Houston. Light snow has fallen approximately 35 times since 1895, more recently on December 4, 2009 and February 23, 2010. Freezing rain, also known as ice storms, are slightly less rare. The most recent ice storms occurred in 1997 and 2007 as well as on February 4, 2011. These storms can be very disruptive since road crews are not equipped to handle such rare events (and motorists are entirely unfamiliar with ice except for half the population which are mostly from northern states). When ice occurs, road and schools are usually closed.
Spring comes with a gradual warm up from winter, lasting from March 20 through May. Temperatures are generally not hot yet, averaging from 75–82 °F (23.9–27.8 °C) in the day and 56–64 °F (13.3–17.8 °C) at night. Spring thunderstorms are common, often with spectacular lightning shows. This rainfall prompts Houston's 10-month long "growing season" to begin. April sees the return of many types of insects, including butterflies and mosquitoes, to return to Houston's warm climate.
Rainfall is the most common form of precipitation in Houston. The wettest month is June, with 5.93 inches (151 mm) of rain. On average, Houston sees 30–40 days of rain per year. The city receives 49.77 inches (1,264 mm) of rain in an average year. The most precipitation to fall in one year was 72.86 inches (1,850.6 mm) which occurred in 1900. Houston has received less than 20 inches (510 mm) of rain only once: 17.66 inches in 1917. 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 flooding. Hurricanes that have the potential to landfall bring severe damage to the area. There have been approximately 7 major hurricanes to hit the Galveston and Houston areas in the past 100 years. Four have done significant damage to Houston.
Hurricanes & tropical storms 
In 1837 the Racer's Storm passed just to the south of the town, raising water levels four feet. The Great Hurricane of 1900 destroyed the nearby (and then much bigger) city of Galveston, which is situated on a barrier island 50 miles southeast of downtown Houston. That hurricane weakened to a tropical storm by the time it reached Houston. The periphery of Hurricane Carla hit the city in 1961, causing major damage to Houston. At the time of landfall, Carla was the most powerful tropical system to hit the Texas coast in over 40 years,. In 1983, the city was struck squarely by Hurricane Alicia, causing one billion dollars damage to the city during a down period in the city's economy.
The most destructive and costly natural disaster in Houston history was Tropical Storm Allison of 2001, which dumped up to 37 inches (940 mm) of rain on parts of the city over a 5-day period. Area flooding was catastrophic and widespread. The storm completely overwhelmed the flood control system and caused 22 deaths in Houston and $6.05 billion (2006 USD) in damage. It is the only tropical storm in history to have its name retired.
Tropical Storm Erin made landfall in August 2007 with strong rains. A total of 9 inches (230 mm) of rain fell at George Bush Intercontinental Airport on August 16 and many roads and neighborhoods were flooded. METRO halted its light rail and bus services in view of the effects. Four deaths in the city were attributed to the storm. The Houston Fire Department reported 72 rescue operations.
Hurricane Ike made landfall near Galveston, Texas in September 2008. Although only a category 2 storm (out of 5), Ike brought moderate rain but high winds for an unusually long duration (upwards of nine hours). The roof of Reliant Stadium (home of the Houston Texans NFL team) was damaged and windows were blown out of several highrise buildings in downtown Houston. Storm surge affected areas around Galveston Bay, stripping some coastal islands of homes. Galveston Island was devastated, looking much like a war zone. Non-emergency access to the island was prohited for many weeks. Hurricane Ike left ninety percent of people in the Houston Area without power. Never before had the city experienced such widespread or long-term power outage: no air conditioning, no refrigeration, no lights, no phones. Day-to-day business slowed immensely. Area grocery stores were stripped bare and sold water and ice for cash by flashlight. Trucks from around the country brought in emergency supplies, especially water and ice. Most of the city was without power for a week—some for 2 to 3 weeks.
Flooding is a recurring problem in Houston. It is especially severe in low-lying areas on the far east end of town along the San Jacinto river. The flat wetlands and paved-over coastal prairie around Houston drains slowly and easily floods. The area is drained by a network of bayous (small, slow-moving rivers; often dredged and enlarged to increase volume) and man-made drainage ditches (usually dry most of the year). Due to the ubiquity of overdevelopment and the huge amounts of concrete, drainage is insufficient during times of especially heavy rainfall. In fall, cool fronts bring in rainstorms and flooding is not uncommon. This might flood certain low-lying intersections, but doesn't generally affect citizens or the business of the city. However, occasionally very heavy thunderstorms dump so much water on the city that widespread congestion and even property damage in low-lying areas results. Tropical Storm Allison in 2001 was the most recent bad flooding incident, and it was so severe that many parts of town that had never flooded before were flooded seriously. Interstate 10 near downtown, which is below grade, was covered by over 10 feet of water.
Unlike Dallas, Houston is not in Tornado Alley. Smaller tornadoes can occur during severe weather. They are most likely to be found along frontal boundaries of an air mass during the spring months. Tornadoes in Houston usually measure a weak 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.
Winter storms 
Due to its very mild winters, Houston has almost no ice, snow or freezes. There are usually a few days of freezing (<32F) temperatures each year. Ice, when it occurs on roads, is cause to shut the entire city down.
Snow is almost unheard of in Houston. When it does occur, it almost invariably melts immediately on the ground with light accumulation on roofs and raised surfaces. Since 1895, it has only snowed thirty five times in Houston, about twice every seven years on average. Such an average is misleading, however, since snow generally only falls once every 10 years. In recent years, snowfall has become much more frequent than normal and multiple snowfall records have been broken.
- December 10, 2008: Ties earliest snowfall record.
- December 4, 2009: Breaks earliest snowfall record. First time snow has fallen in two consecutive years.
- February 23, 2010: First time snow has fallen in three consecutive years.
The 2004 Christmas Eve snowstorm brought a never-before, White Christmas to the region. Average annual snowfall is very, very little above zero, being less than the measurable amount of 0.1 inches (2.5 mm). In descending order of frequency, the most snow has fallen in January, followed by February, December, and finally a single occurrence on March 10, 1932, which was also the lowest recorded temperature for that month, 22 °F (−6 °C).
Environmental issues 
Houston has had a troubled past with pollution of many types. This is due to the fact that Houston has been the home for the oil and gas industry since its inception in the early 1900s when there was little environmental regulation. Harris County, where the bulk of the City has been historically located, 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 hazardous to humans in various ways.
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, 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. Ground-level ozone, or smog, is Houston’s predominant air pollution problem. In 2011, Houston was ranked as the 17th most polluted city in the US according to the American Lung Association. A 2007 assessment found the following twelve air pollutants to be definite risks to health in Houston:
- ozone - respiratory and cardiovascular effects
- particulates less than 2.5 μm in diameter (PM2.5) - 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 neighborhood, in eastern Houston had the highest annual averages of 1,3-Butadiene of any area in Texas. Houston's air quality has often been compared to Los Angeles and Beijing.
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. To date it has had limited success and been a source of controversy and cost overruns.
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. The Port of Houston has not seen any major cleaning attempts.
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