Many of Birmingham's television and radio broadcast towers are lined up along this prominent ridge. The "Over the Mountain" area, including Shades Valley, Shades Mountain and beyond, was largely shielded from the industrial smoke and rough streets of the industrial city. This is the setting for Birmingham's more affluent suburbs of Mountain Brook, Vestavia Hills, Homewood, Pelham, and Hoover. South of Shades Valley is the Cahaba River basin, one of the most diverse river ecosystems in the United States. Sand Mountain, a lower ridge, flanks the city to the north and divides Jones Valley from much more rugged land to the north. The Louisville and Nashville Railroad (now CSX Transportation) enters the valley through Boyles Gap, a prominent gap in the long low ridge. Ruffner Mountain, due east of the heart of the city, is home to Ruffner Mountain Nature Preserve, one of the largest urban nature reserves in the U.S.  Birmingham is west of Atlanta, north of Montgomery, northeast of Meridian, Mississippi, southeast of Memphis, south of Nashville, and southwest of Chattanooga, all via Interstate highways. According to the U.S. Census Bureau, the city has an area of , of which are land and , or 1.71%, are water. Birmingham has numerous suburbs. As with many major areas, most of the metropolitan population lives outside the city boundaries. In 2007, the metropolitan area was made up of 7 counties, 102 cities, and 21 school districts. Since then Alabaster and Pelham have broken away from the Shelby County School System to form their own school systems. Some analysts argue that the region suffers from having so many suburbs; companies play jurisdictions against each other to gain tax and other financial incentives for relocation, resulting in no net gain in the area's economy. Suburbs in the Birmingham–Hoover metropolitan area by order of population (2016 estimates):  Birmingham has a humid subtropical climate, characterized by hot summers, mild winters, and abundant rainfall. January has a daily mean temperature of , and there is an average of 47 days annually with a low at or below freezing, and 1.4 where the high does not surpass freezing. July has a daily mean temperature of ; highs reach or exceed on 55 days per year and on 2 or 3. Precipitation is relatively well-distributed throughout the year, with March the wettest month on average, and October the driest. Snow occasionally falls during winter, but many winters pass with no snow or only a trace.