Louisville is located at (38.228870, -85.749534). According to the U.S. Census Bureau, Louisville Metro (in 2000 measurements for Jefferson County) has a total area of 1,032 km² (399 mi²). 997 km² (385 mi²) of it is land and 35 km² (13 mi²) of it (3.38%) is water.
Although the soils and underlying rocks officially put Louisville in the Bluegrass region, the city's landscape is better described as being in a very wide part of the Ohio River flood plain. Louisville's part of the valley is located between two plateaus, the karst plateau of Southern Indiana and the Bluegrass plateau of Kentucky, both with an elevation of around 900 feet. Elevations drop off the Indiana plateau very sharply via the Muldraugh Escarpment, whereas the rise in elevation up to the Bluegrass plateau is done more gradually.
The flood plain is much longer north to south than it is east to west. For example, within several miles of downtown, the Highlands sitting at 540 feet is out of the thousand year flood plain, whereas areas 10 miles from downtown such as Fairdale and Okolona (both between seven and 11 miles from the river) have the same elevation as downtown Louisville. Most areas in the east end have an elevation from 600 to 700 feet, which, with the typically east bound winds, trap in heat and pollutants.
Areas along and west of the south fork of Beargrass Creek (and more generally, I-65) are located where the Ohio River once ran, so the land here is very flat and is composed of harder rocks. Prior to urbanization much of this area was composed of wetlands — early roads through it were laid over wooden planks. This history is occasionally still readily evident in street names, for example the spoke road Poplar Level, whose name describes its original construction on planks of poplar. 3rd Street was formerly called Central Plank Road for the same reason. As industry, namely Standiford Field airport, moved into the area in the 1950s most creeks through the area were rerouted into ditches to alleviate the area's poor drainage and constant flooding.
Areas east of I-65 were generally not in the flood plain and thus are mostly gentle rollings hills composed of soft loess soils, hence the reason roads here (such as Eastern Parkway) are very prone to potholes. The southern quarter of Jefferson County is in the scenic and rugged Knobs region. This is the only part of Jefferson County to not have experienced any urbanization and is today almost entirely parkland for the Jefferson Memorial Forest. The eastern third is in the Eden Shale Hills section of the Bluegrass region and has also experienced less urbanization than the flood plain, although that is starting to change.
The Louisville-Jefferson County, KY-IN Metropolitan Statistical Area (MSA), the 42nd largest in the United States, includes the Kentucky counties of Jefferson (contiguous with Louisville Metro), Bullitt, Henry, Meade, Nelson, Oldham, Shelby, Spencer and Trimble. The southern Indiana counties Clark, Floyd, Harrison and Washington are also included in the Louisville MSA. This MSA is included in the Louisville-Elizabethtown-Scottsburg, KY-IN Combined Statistical Area (CSA), which also includes the Elizabethtown, KY MSA (composed of Hardin and Larue Counties) as well as the Scottsburg, IN Micropolitan Statistical Area. The Louisville CSA ranks 31st in the USA in population.
Louisville's Metro Area was expanded more than any other in the country during a March 2003 overhaul of U.S. Metropolitan Area statistics by the federal government. In the 2000 census, even very fast growing counties such as Spencer County weren't included. The Metro Area's ranking rose from 49th to 42nd, and the added Combined Statistical Area measured the area as the nation's 31st largest. The total Metro area population also increased dramatically from just over 1 million to nearly 1.4 for the CSA.
17% of the state's population lives in Jefferson County and 25% live in counties in the Louisville CSA, and also Jefferson County has 2.5 times more people than Kentucky's second most populous county, Fayette County. 12 of the 15 buildings in Kentucky over 300 feet are located in Downtown Louisville. Almost 40% of the population growth in Kentucky are in Louisville's CSA counties.
Louisville is located on the northern limit of the humid subtropical climate. Summers are hot and humid with mildly warm evenings. The mean annual temperature is 56 °F (13 °C), with an average annual snowfall of 16.4 inches (41 cm) and an average annual rainfall of 44.53 inches (1131 mm). The wettest seasons are the spring and summer, although rainfall is fairly constant all year round. During the winter, particularly in January and February, several days of snow can be expected, allowing for winter sports. January is the coldest month with average highs of 41 °F and average lows of 25 °F (5 to −4 °C) and July the hottest month with average high and low temperatures from 87 to 69.8 °F (31 and 21 °C). The highest recorded temperature was 105 °F (41 °C) on July 14, 1954, and the lowest recorded temperature was −22 °F (−30 °C) on January 19, 1994. However, in any season, temperatures can vary widely day by day, because of Louisville's location where many fronts often converge. Severe weather is not uncommon; the area is prone to almost all types of non-tropical weather extremes, including tornadoes, severe thunderstorms, ice storms and extreme heat and cold.
Much like the San Fernando Valley in Los Angeles, Louisville's Ohio River Valley location traps air pollution. The city is ranked by Environmental Defense as America's 38th worst city for air quality. Louisville also often exemplifies the heat island effect. Temperatures in commercial areas and in the industrialized areas along interstates are often higher than in the suburbs, particularly the shaded areas, like Anchorage, where temperatures are often five degrees cooler.
Louisville's lowest solar noon is 28.4 degrees with the shortest daylength being 9 hours and 30 seconds, both occurring from December 17-26. The city's highest solar noon is 75.2 degrees with the longest daylength being 14 hours and 39 seconds, both occurring from June 17-25. The city's March and September equinox occurs at 50.5 degrees.