Climate

Richmond has a Warm Temperate Climate and a humid subtropical climate (Köppen Cfa), with hot and humid summers and generally cool winters. The mountains to the west act as a partial barrier to outbreaks of cold, continental air in winter; Arctic air is delayed long enough to be modified, then further warmed as it subsides in its approach to Richmond. The open waters of the Chesapeake Bay and Atlantic Ocean contribute to the humid summers and mild winters. The coldest weather normally occurs from late December to early February, and the January daily mean temperature is 37.9 °F (3.3 °C), with an average of 6.0 days with highs at or below the freezing mark.^[43] Downtown areas and suburbs to the east of Richmond are situated in USDA Hardiness zones 7b while surrounding suburban and rural areas to the west are in the 7a Hardiness Zone.^[44] and temperatures seldom lower to 0 °F (−18 °C), with the most recent subzero (°F) reading occurring on January 28, 2000, when the temperature reached −1 °F (−18 °C).^[45] The July daily mean temperature is 79.3 °F (26.3 °C), and high temperatures reach or exceed 90 °F (32 °C) approximately 43 days out of the year; while 100 °F (38 °C) temperatures are not uncommon, they do not occur every year.^[46] Extremes in temperature have ranged from −12 °F (−24 °C) on January 19, 1940 up to 107 °F (42 °C) on August 6, 1918.^[a]
Precipitation is rather uniformly distributed throughout the year. However, dry periods lasting several weeks do occur, especially in autumn when long periods of pleasant, mild weather are most common. There is considerable variability in total monthly amounts from year to year so that no one month can be depended upon to be normal. Snow has been recorded during seven of the twelve months. Falls of 3 inches (7.6 cm) or more within 24 hours occur an average once per year.^[43] Annual snowfall, however, is usually light, averaging 10.5 inches (27 cm) per season.^[43] Snow typically remains on the ground only one or two days at a time, but remained for 16 days in 2010 (January 30 to February 14). Ice storms (freezing rain or glaze) are not uncommon, but they are seldom severe enough to do any considerable damage.
The James River reaches tidewater at Richmond where flooding may occur in every month of the year, most frequently in March and least in July. Hurricanes and tropical storms have been responsible for most of the flooding during the summer and early fall months. Hurricanes passing near Richmond have produced record rainfalls. In 1955, three hurricanes brought record rainfall to Richmond within a six-week period. The most noteworthy of these were Hurricane Connie and Hurricane Diane that brought heavy rains five days apart. And in 2004, the downtown area suffered extensive flood damage after the remnants of Hurricane Gaston dumped up to 12 inches (300 mm) of rainfall.^[48]
Damaging storms occur mainly from snow and freezing rain in winter and from hurricanes, tornadoes, and severe thunderstorms in other seasons. Damage may be from wind, flooding, or rain, or from any combination of these. Tornadoes are infrequent but some notable occurrences have been observed within the Richmond area.
Based on the 1981–2010 period, the average first occurrence of at or below freezing temperatures in the fall is November 4 and the average last occurrence in the spring is April