According to the Köppen climate classification, Richmond has a humid subtropical climate , with hot, humid summers and moderately cold winters. The Trewartha classification defines Richmond as Temperate Oceanic Climate due to winter chill. 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 cool 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. Richmond’s Downtown and areas south and east of downtown are in USDA Hardiness zones 7b. Surrounding suburbs and areas to the north and west of Downtown are in Hardiness Zone 7a. Temperatures seldom fall below 0 °F (−18 °C), with the most recent subzero reading on January 7, 2018, when the temperature reached −3 °F (−19 °C). 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 a year; 100 °F (38 °C) temperatures are not uncommon but do not occur every year. Extremes in temperature have ranged from −12 °F (−24 °C) on January 19, 1940, up to 107 °F (42 °C) on August 6, 1918. The record cold maximum is 11 °F (−12 °C), set on February 11 and 12, 1899. The record warm minimum is 81 °F (27 °C), set on July 12, 2011.
Precipitation is rather uniformly distributed throughout the year. Dry periods lasting several weeks sometimes 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 12 months. Falls of 4 inches (10 cm) or more within 24 hours occur once a year on average. Annual snowfall is usually moderate, averaging 10.5 inches (27 cm) per season. Snow typically remains on the ground for only one or two days, but remained for 16 days in 2010 (January 30 to February 14). Ice storms (freezing rain or glaze) are not uncommon, but are seldom severe enough to do considerable damage.
The James River reaches tidewater at Richmond, where flooding may occur in any 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 were Hurricane Connie and Hurricane Diane, which brought heavy rains five days apart. In 2004, the downtown area suffered extensive flood damage after the remnants of Hurricane Gaston dumped up to 12 inches (300 mm) of rain.
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, rain, or any combination of these. Tornadoes are infrequent but some notable ones have been observed in the Richmond area.
Downtown Richmond averages 84 days of nighttime frost annually. Nighttime frost is more common in areas north and west of Downtown and less common south and east of downtown. From 1981 to 2010 the average first temperature at or below freezing was on October 30 and the average last one on April 10.