Climate

Further information: Geography of St. Louis § Climate

The Captains' Return statue inundated by the Mississippi River, 2010.

St. Louis lies in the transitional zone between the humid continental climate type and the humid subtropical climate type (Köppen Dfa and Cfa, respectively), with neither large mountains nor large bodies of water to moderate its temperature. The city experiences hot, humid summers, and chilly to cold winters. It is subject to both cold Arctic air and hot, humid tropical air from the Gulf of Mexico. The average annual temperature recorded at nearby Lambert–St. Louis International Airport, is 57.1 °F (13.9 °C). Both 100 and 0 °F (38 and −18 °C) temperatures can be seen on an average 2 or 3 days per year.^[30] Average annual precipitation is about 41.0 inches (1,040 mm),^[30] but annual precipitation has ranged from 20.59 in (523 mm) in 1953 to 61.24 in (1,555 mm) in 2015.^[31]
St. Louis experiences thunderstorms 48 days a year on average.^[32] 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.

[show]Climate data for St. Louis, Missouri (Lambert–St. Louis Int'l), 1981−2010 normals,[a] extremes 1874−present[b]

Flora and fauna

Tower Grove Park in spring

The Missouri Botanical Garden

Before the founding of the city, the area was mostly prairie and open forest. Native Americans maintained this environment, good for hunting, by burning underbrush. 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 areas of the city are 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 officials are trying to manage because of its damage to native trees. It is removed from some parks.
Large mammals found in the city include urbanized coyotes and white-tailed deer. Eastern gray squirrel, cottontail rabbit, and other rodents are abundant, as well as the nocturnal Virginia 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 along 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 US. The Eurasian tree sparrow, an introduced species, is limited in North America to the counties surrounding St. Louis. The city has special sites for birdwatching of migratory species, including Tower Grove Park.
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, which are found in nearly every pond. Some years have outbreaks of cicadas or ladybugs. Mosquitoes, no-see-ums, and houseflies are common insect nuisances, especially in July and August; because of this, windows are nearly universally fitted with screens. Invasive populations of honeybees have sharply declined in recent years. Numerous native species of pollinator insects have recovered to fill their ecological niche, and armadillos have been regularly seen throughout the St. Louis area, especially since 2005.^[36]