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. Political geography and population The Louisville-Jefferson County, KY-IN Metropolitan Statistical Area (MSA), the 43rd-largest in the United States, includes the Kentucky counties of Jefferson (coterminous 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. 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. Seventeen percent of the state's population lives in Jefferson County and 25% live in counties in the Louisville CSA, and also Jefferson County has two-and-a-half times more people than Kentucky's second-most populous county, Fayette County. Twelve 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. Climate Louisville has a humid subtropical climate (Köppen Cfa), typical of the Upper South, with four distinct seasons and is located in USDA hardiness zones 6b and 7a. Spring-like conditions typically begin in mid-to-late March, summer from mid-to-late-May to late September, with fall in the October–November period. Seasonal extremes in both temperature and precipitation are not uncommon during early spring and late fall; severe weather is not uncommon, with occasional tornado outbreaks in the region. Winter typically brings a mix of rain, sleet, and snow, with occasional heavy snowfall and icing. Louisville averages 5.8 days with low temperatures