Revival styles. Neighborhoods Evansville has thirteen neighborhoods that have qualified as historic districts and are listed on the National Register of Historic Places. Climate Evansville lies within the northern limits of the humid subtropical climate (Köppen Cfa), and straddles the border between USDA plant hardiness zones 6b and 7a. Summers are hot and humid, winters are cold to cool. Average temperatures range from in January to in July. Annual precipitation averages , including an average seasonal snowfall of . Evansville winters can range from just of snowfall in 2011–12, up to in 1969–70. On average, there are 41 days annually with a maximum temperature of or above and 17 days with a maximum at or below freezing; the mean first and last freeze dates are October 26 and April 7, resulting in a frost-free period of 201 days. Extreme temperatures range from on February 2, 1951 up to on July 28, 1930; the record cold maximum of was set on January 20, 1985 and December 22, 1989, while, conversely, the record warm minimum of was last reached July 8, 1980. Pollution In August 2018, the mayor of Evansville sent a letter to the Ohio River Valley Water Sanitation Commission (ORVWSO) opposing a proposal to eliminate pollution control standards for the Ohio River. Evansville is located downstream from the river's origin. Sources of pollution that affect water quality include agricultural runoff, raw sewage discharges from combined sewer overflows, and toxic chemicals released by companies with water pollution permits. The state of Indiana issues a fish consumption advisory for fish from the Ohio River based on PCB contamination. The recommended consumption limit for most fish, including carp, striped bass and flathead catfish is no more than 8 oz. per month, but for channel catfish, the recommendation is only 8oz every two months. Six very large coal-fired power plant complexes operate within 30 miles of Evansville: Indiana-Michigan Power's Rockport Generating Station, near Rockport, Indiana, AES Indiana's Petersburg Generating Station near Petersburg, and Duke Energy's Gibson Generating Station near Mount Carmel. Evansville-Based Vectren operates the other two; the A. B. Brown Generating Station, located just west of Evansville, and Warrick County Generating Station/F. B. Culley Generating Station complex, east of Newburgh, largely owned by Alcoa. In addition, another coal fired power plant complex, The R.D. Green Station, operated by Touchstone Energy's Big Rivers Electric, exists 20 miles south of Evansville, near Sebree, Kentucky. The