The climate is humid subtropical (Köppen: Cfa), but all around Greater St. Louis has a humid continental climate (Dfa) through the USA isoterm, with a winter that sustains in the coldest month temperatures below 0 ° C more easily, clear evidence of an island of urban heat, which in the future may cover an even larger area and agglutinate cities and villages to the south.^[3] It straddles the border between USDA Plant Hardiness Zones 6B and 7A,^[4] indicating the coldest temperature of the year is typically around {{convert|0|°F|0}}. With neither large mountains nor large bodies of water to moderate its temperature, it is subject to both cold Arctic air and hot, humid tropical air from the Gulf of Mexico. The city has four distinct seasons. Spring is the wettest season and produces severe weather ranging from tornadoes to winter storms. Summers are hot and humid; temperatures of {{convert|90|°F|0}} or higher occur 43 days a year.^[5] The average window for such temperatures is May 19 thru September 14.

Fall is mild with lower humidity and can produce intermittent bouts of heavy rainfall with the first freeze of the season on average falling on November 2 (the last on average falls on April 3); the first measurable ({{convert|0.1|in|cm|sigfig=2}}) snow, often not counting flurries, on average occurs on December 4 (the last on average falls on March 17). Winters can be cold and snowy with temperatures frequently below freezing. Winter storm systems, such as Alberta clippers and Panhandle hooks, can bring days of heavy freezing rain, ice pellets, and snowfall.

The average annual temperature recorded at nearby Lambert–St. Louis International Airport, is {{convert|57.1|°F|1}}, and average precipitation is about {{convert|41.0|in|sigfig=3}}. The daily average temperature in July is {{convert|80.0|°F|1}}, while in January it is {{convert|31.8|°F|1}}, although this varies from year to year. Both {{convert|100|°F|1}} and {{convert|0|°F|1}} temperatures can be seen on an average 2 or 3 days per year. The official record low is {{convert|−22|°F|0}} on January 5, 1884, although there were unofficial readings of {{convert|-23|°F|0}} on January 29, 1873; and the record high is {{convert|115|°F|0}} on July 14, 1954;^[6] the coldest high on record was {{convert|−5|°F|0}} on December 24, 1983, while, conversely, the warmest low on record was {{convert|86|°F|0}} on July 25, 2012 and July 24, 1901. July 2012 was the hottest month in the 138-year recorded weather temperatures in St. Louis history starting in 1874, with an average daily temperature of {{convert|88.1|°F|1}}.^[6]

Winter (December through February) is the driest season, with an average {{convert|7.5|in|0|abbr=on}} of precipitation. The average seasonal snowfall is {{convert|18.2|in|cm|0}}, typically falling from December to March. The heaviest one-day snowfall total was {{convert|12.8|in|cm|1|abbr=on}} on February 26, 1906. Spring (March through May), is typically the wettest season, with {{convert|11.7|in|0|abbr=on}} of precipitation; however, the heaviest 24-hour rainfall total was {{convert|6.85|in|1|abbr=on}} on August 20, 1915. Dry spells lasting one to two weeks are common during the growing seasons.

St. Louis experiences thunderstorms 48 days a year on average.^[7] Especially in the spring, these storms can often be severe, with high winds, large hail and tornadoes. Lying within the hotbed of Tornado Alley, St. Louis reigns as one of the most frequently tornadic metropolitan areas, and has an extensive history of particularly damaging tornadoes. Severe flooding, such as the Great Flood of 1993, may occur in spring and summer; the (often rapid) melting of thick snow cover upstream either the Missouri or Mississippi Rivers can contribute to springtime flooding.

Some late autumns feature the warm weather known as Indian summer; some years see roses in bloom as late as early December.

Flora and fauna

Before the founding of the city, the area was prairie and open forest maintained by burning by Native Americans. Trees are mainly oak, maple, and hickory, similar to the forests of the nearby Ozarks; common understory trees include eastern redbud, serviceberry, and flowering dogwood. Riparian areas are forested with mainly American sycamore. Most of the residential area of the city is planted with large native shade trees. The largest native forest area is found in Forest Park. In autumn, the changing color of the trees is notable. Most species here are typical of the Eastern Woodland, although numerous decorative non-native species are found; the most notable invasive species is Japanese honeysuckle, which is actively removed from some parks.

Large mammals found in the city include urbanized coyotes and occasionally a stray whitetail deer. eastern gray squirrel, cottontail rabbit, and other rodents are abundant, as well as the nocturnal and rarely seen opossum. Large bird species are abundant in parks and include Canada goose, mallard duck, as well as shorebirds, including the great egret and great blue heron. Gulls are common along the Mississippi River; these species typically follow barge traffic. Winter populations of bald eagles are found by the Mississippi River around the Chain of Rocks Bridge. The city is on the Mississippi Flyway, used by migrating birds, and has a large variety of small bird species, common to the eastern U.S. The Eurasian tree sparrow, an introduced species, is limited in North America to the counties surrounding St. Louis. Tower Grove Park is a well-known birdwatching area in the city.

Frogs are commonly found in the springtime, especially after extensive wet periods. Common species include the American toad and species of chorus frogs, commonly called "spring peepers" that are found in nearly every pond. Some years have outbreaks of cicadas or ladybugs. Mosquitos and houseflies are common insect nuisances; because of this, windows are nearly universally fitted with screens, and "screened-in" porches are common in homes of the area. Populations of honey bees have sharply declined in recent years, and numerous species of pollinator insects have filled their ecological niche.

Adjacent communities

The following communities border the city of St. Louis directly:

In addition to the above named places, there are unincorporated parts of Madison County, Illinois; St. Clair County, Illinois; and St. Louis County, Missouri which border St. Louis. The Illinois communities of Brooklyn and Venice lie across the Mississippi River, but do not border St. Louis because the river itself is not part of their territory.

See also

• Climate of Missouri

References