The Geography of Atlanta encompasses , of which is land and is water. The city is situated among the foothills of the Appalachian Mountains, and at above mean sea level, Atlanta has the highest elevation among major cities east of the Mississippi River. Atlanta straddles the Eastern Continental Divide, such that rainwater that falls on the south and east side of the divide flows into the Atlantic Ocean, while rainwater on the north and west side of the divide flows into the Gulf of Mexico. Atlanta sits atop a ridge south of the Chattahoochee River, which is part of the ACF River Basin. Located at the far northwestern edge of the city, much of the river's natural habitat is preserved, in part by the Chattahoochee River National Recreation Area.
Climate
The climate of Atlanta and its metropolitan area is humid subtropical (Cfa) according to the Köppen classification, with four seasons including hot, humid summers and cool winters that are occasionally cold by the standards of the southern United States; the city and its immediate suburbs are located in USDA Plant Hardiness Zone 8a, although the far northern suburbs begin to transition to Zone 7b.
Summers are long and consistently hot and humid. The daily average temperature in July is , with temperatures occasionally exceeding , and slight breezes, and typically a 20–40% chance of afternoon thunderstorms. During the summer afternoon thunderstorms, temperatures may suddenly drop below with locally heavy rainfall.
January averages , with temperatures in the suburbs slightly cooler. Warm, maritime air can bring springlike conditions while strong Arctic air masses can push lows to between . Snow may not occur in every season in the city and inner suburbs but does every season in the northern metro. When snow falls it is almost always during the period of December through March: there have occurred only three measurable falls outside these months in the past ninety years, the largest being on November 11, 1968.
Typical of the southeastern U.S., Atlanta receives abundant rainfall, which is relatively evenly distributed throughout the year, though spring and early fall are markedly drier. Average annual rainfall is about , with late winter and early spring (as well as July) being the wettest and fall (especially October) being the driest. Despite having far fewer rainy days, average yearly rainfall is higher here than in the Seattle area, especially due to heavy thunderstorms and occasional tropical depressions.
Extremes Temperatures at or above now occur on 44 days per year (up from 37 previously); though there have been as many as 91 days in 2019, and as few as 2 days in 1967. Overnight freezes can be expected on 40 days, but the high temperature rarely fails to climb above the freezing mark. In very cold winter months with high-latitude blocking, averages can occasionally fall below freezing: the coldest month was January 1977 which averaged and which amazingly saw Atlanta average colder than Anchorage, Alaska, almost 30 degrees latitude further north. The only other month with a subfreezing mean has been January 1940 with an average of and a record cold mean maximum of .
Snowfall averages per season. The heaviest single storm brought on January 23, 1940, the most snow in one calendar day, and the most in a calendar month; the most snowfall in a season (July 1 through June 30 of the next year) is in 1935–36. True blizzards are rare but possible; the Storm of the Century, which affected the region on March 12–14, 1993, is one such example, bringing snowdrifts up to high in some parts of north Georgia. Ice storms usually cause more trouble than does snowfall; the most severe such storms may have occurred on January 7, 1973, and January 9, 2011. In 2010, Atlanta had its first White Christmas since 1882 and 1883. Later that same winter (the third-coldest ever), a major snow-and-ice storm almost prevented the inauguration of the new governor of Georgia, and crippled the region for two days, with snow still left more than a week later in some places.
Official weather recordkeeping began in Atlanta in 1878, on the morning of October 3. Since then, the highest recorded temperatures at Atlanta were on June 30, 2012; the hottest month on record is August 2007, with a mean temperature of . The lowest recorded temperatures were and on January 20 and 21 of 1985, and on February 13, 1899. There was also an official recording of in 1985 in Marietta. The coldest high temperature was , again on February 13, 1899, while, conversely, the hottest low temperature was on August 8, 2007.
The rainiest month ever was July 1994, when Tropical Storm Alberto dumped massive amounts of rain on parts of the state and the south metro area, bringing at Atlanta, over three times a normal July. Flooding was a major problem in those areas, and further down-state it was a major disaster. The driest months were October 1963 and October 2024, when in both situations record dry spells occurred over the entire eastern and southern United States (except Florida peninsula), leaving Atlanta with only a trace of precipitation for the entire month.
Data
Effect on vegetation Some palm trees like palmetto and cacti like prickly pear can withstand the cold nights, complementing numerous flowering pansies and a few camellias, and other mild-winter-friendly plants of the region. The growing season in the area lasts several months, hardy plants being as early as mid February, and others from mid March to late October, when the last and first cold snaps usually occur. Spring weather is pleasant but variable, as cold fronts often bring strong or severe thunderstorms to almost all of the eastern and central U.S. Pollen counts tend to be extraordinarily high in the spring, regularly exceeding 2000 particles per cubic meter in April and causing hay fever, sometimes even in people not normally prone to it. Pine pollen leaves a fine yellow-green film on everything for much of that month. The rain helps wash out Atlanta's abundant oak, pine, and grass pollens, and fuels beautiful blooms from native flowering dogwood trees, as well as azaleas, forsythias, magnolias, and peach trees (both flowering-only and fruiting). The citywide floral display runs during March and April, and inspires the Atlanta Dogwood Festival, one of Atlanta's largest. Fall is also pleasant, with less rain and fewer storms, and leaves changing color from late October to mid-November, especially during drier years. A secondary peak in severe storms also occurs around the second week of November.
Effect of geography The area's geography affects the weather as well. An anticyclone over the Northeastern U.S. will blow cold air over the warmer Atlantic Ocean, forming a wedge or marine layer up against the mountains. This east or northeast wind will often blow down into the metro area in winter or even spring (sometimes fall and very rarely summer), dramatically lowering the temperature and bringing clouds and often fog or mist, along with a swift breeze. The temperature gradient across the sprawling metro Atlanta can be as much as 20 °F or 10 °C, occasionally even more. In winter this can be a curse, bringing freezing rain to exposed objects on the north and/or east sides of town, and occasionally very dangerously to the ground and roads. Later in the spring however, it can be a great blessing, as it often protects the area from severe thunderstorms and tornadoes, with the cool air acting like a fire extinguisher to the storms. The wedge may occasionally go the entire way through central Georgia and even into Alabama in the strongest conditions, while still leaving areas of northwest Georgia much warmer than the metro area. Conversely, shallow and heavy cold air from the northwest may be blocked by the mountains, preventing snow.
The local geography also plays a role in the day-to-day weather, with the shallow valleys to the southwest (rather than the mountains to the northeast) cooling rapidly on clear and calm nights, particularly when the humidity is low. Peachtree City and especially Newnan often report dramatically lower temperatures (by as much as ) on the 10 pm and 11 pm news, and will not drop much further, while the city (built on a ridge) will continue falling slowly but never reach that low. This type of dramatic difference in microclimate is somewhat unusual for a place not near large mountains or bodies of water.
Extreme weather Tropical cyclones Hurricane Opal brought sustained tropical storm conditions to the area one night in early October 1995, uprooting hundreds of trees (mainly oaks) and causing widespread power outages, after soaking the area with rain for two days prior. The western metro area caught the worst of the storm, gusting to nearly officially at Marietta.
Such events are very rare so far inland, some inland from the Gulf of Mexico where most of the storms come from; however some areas particularly east and south of the city received similar damage from the wide wind field of Hurricane Irma in September 2017, with a gust to at Atlanta's airport and sustained winds up to there. Record-cool high temperatures of caused by cold-air damming against the Appalachians served to eliminate the normal tornado risk in north Georgia and to weaken the storm faster than expected, reducing the anticipated damage to the area. Less than a month later in early October 2017, the much smaller Hurricane Nate was forecast to pass rapidly through northwest Georgia as a weak tropical storm, expected to cause far fewer issues to the metro area than Irma. These two storms caused the first tropical storm watches (and for Irma, warnings) for the area since these were allowed to be issued for inland locations instead of just coastal ones.
Tornadoes Since 1950, some metro counties have been hit more than 20 times by tornadoes, with Cobb (26) and Fulton (22) being two of the highest in the state. (Note that some tornadoes may have occurred at the same time, or in two different counties.) Another struck the Georgia Governor's Mansion in 1975. The Dunwoody tornado in early April 1998 was the worst tornado to have struck the suburban area. Since then, many counties have reinstalled civil defense sirens removed after the Cold War.
On March 14, 2008, an EF2 tornado hit downtown Atlanta with winds up to . The tornado caused damage to Philips Arena, the Westin Peachtree Plaza Hotel, the Georgia Dome, Centennial Olympic Park, the CNN Center, and the Georgia World Congress Center. It also damaged the nearby neighborhoods of Vine City to the west and Cabbagetown, and Fulton Bag and Cotton Mills to the east. While there were dozens of injuries, only one fatality was reported. City officials warned it could take months to clear the devastation left by the tornado.
Winter storms The area experiences a winter storm with significant snowfall about once each year, however this can be extremely irregular. During the 2000s, only four major snows occurred (December 2000, January 2002, January 2008, and March 2009), while three occurred in early 2010 (an El Niño year) alone, making it the snowiest winter since the 1970s. Despite predictions of a warm and dry winter due to La Niña developing the following summer, additional fell on December 25, giving the city (and its northern and western suburbs) its first true white Christmas in over a century. The only other measurable snows on that date were in 1881, and in 1882. A trace last fell on Christmas in 1993, and a dozen other years before that.