Geography of Atlanta

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Atlanta's Piedmont Park with a blanket of winter snow

The Geography of Atlanta encompasses 132.4 square miles (342.9 km2), of which 131.7 square miles (341.1 km2) is land and 0.7 square miles (1.8 km2) is water. The city is situated among the foothills of the Appalachian Mountains, and at 1,050 feet (320 m) above mean sea level, Atlanta has the highest elevation among major cities east of the Mississippi River.[1][2] 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.[3] 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.[4]

Climate

Atlanta
Climate chart (explanation)
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F
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█ Average max. and min. temperatures in °F
█ Precipitation totals in inches
Metric conversion
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█ Average max. and min. temperatures in °C
█ Precipitation totals in mm

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.[5]

Summers are long and consistently hot and humid. The daily average temperature in July is 80.2 °F (26.8 °C), with temperatures occasionally exceeding 100 °F or 37.8 °C, and slight breezes, and typically a 20–40% chance of afternoon thunderstorms. During the summer afternoon thunderstorms, temperatures may suddenly drop below 85 °F or 29.4 °C with locally heavy rainfall.

January averages 43.3 °F or 6.3 °C, with temperatures in the suburbs slightly cooler. Warm, maritime air can bring springlike conditions while strong Arctic air masses can push lows to between 20 and 10 °F (−6.7 and −12.2 °C). 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 1.0 inch or 2.5 centimetres on November 11, 1968.[6]

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 49.7 inches (1,260 mm), 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

tropical depressions
.

Extremes

Temperatures at or above 90 °F (32.2 °C) 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.[6] 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 29.3 °F (−1.5 °C) and which amazingly saw Atlanta average 2.7 °F (1.5 °C) colder than Anchorage, Alaska, almost 30 degrees latitude further north.[7] The only other month with a subfreezing mean has been January 1940 with an average of 29.6 °F (−1.3 °C) and a record cold mean maximum of 38.0 °F (3.3 °C).[6]

Snowfall averages 2.9 inches (7.4 cm) per season.[6] The heaviest single storm brought 8.3 in (21 cm) 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 10.9 in (28 cm) in 1935–36.[6] 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 6 ft (1.8 m) high in some parts of north Georgia.[8] 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.[9] 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

January 20 and 21 of 1985, and −9 °F (−22.8 °C) on February 13, 1899. There was also an official recording of −10 °F (−23.3 °C) in 1985 in Marietta. The coldest high temperature was 7 °F (−13.9 °C), again on February 13, 1899, while, conversely, the hottest low temperature was 82 °F (27.8 °C) on August 8, 2007.[6]

The rainiest month ever was July 1994, when

Flooding was a major problem in those areas, and further down-state it was a major disaster. The driest month was October 1963 when a record dry spell occurred over the entire eastern and southern United States, leaving Atlanta with only a trace of precipitation for the entire month.[10]

Data

Climate data for Atlanta (Hartsfield–Jackson Int'l), 1991–2020 normals,[a] extremes 1878–present[b]
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Record high °F (°C) 79
(26) 		81
(27) 		89
(32) 		93
(34) 		97
(36) 		106
(41) 		105
(41) 		104
(40) 		102
(39) 		98
(37) 		84
(29) 		79
(26) 		106
(41)
Mean maximum °F (°C) 70.3
(21.3) 		73.5
(23.1) 		80.8
(27.1) 		84.7
(29.3) 		89.6
(32.0) 		94.3
(34.6) 		95.8
(35.4) 		95.9
(35.5) 		91.9
(33.3) 		85.0
(29.4) 		77.5
(25.3) 		71.5
(21.9) 		97.3
(36.3)
Mean daily maximum °F (°C) 54.0
(12.2) 		58.2
(14.6) 		65.9
(18.8) 		73.8
(23.2) 		81.1
(27.3) 		87.1
(30.6) 		90.1
(32.3) 		89.0
(31.7) 		83.9
(28.8) 		74.4
(23.6) 		64.1
(17.8) 		56.2
(13.4) 		73.2
(22.9)
Daily mean °F (°C) 44.8
(7.1) 		48.5
(9.2) 		55.6
(13.1) 		63.2
(17.3) 		71.2
(21.8) 		77.9
(25.5) 		80.9
(27.2) 		80.2
(26.8) 		74.9
(23.8) 		64.7
(18.2) 		54.2
(12.3) 		47.3
(8.5) 		63.6
(17.6)
Mean daily minimum °F (°C) 35.6
(2.0) 		38.9
(3.8) 		45.3
(7.4) 		52.5
(11.4) 		61.3
(16.3) 		68.6
(20.3) 		71.8
(22.1) 		71.3
(21.8) 		65.9
(18.8) 		54.9
(12.7) 		44.2
(6.8) 		38.4
(3.6) 		54.1
(12.3)
Mean minimum °F (°C) 17.3
(−8.2) 		23.2
(−4.9) 		28.1
(−2.2) 		36.9
(2.7) 		47.6
(8.7) 		59.9
(15.5) 		65.6
(18.7) 		64.5
(18.1) 		53.4
(11.9) 		38.7
(3.7) 		29.2
(−1.6) 		23.8
(−4.6) 		15.2
(−9.3)
Record low °F (°C) −8
(−22) 		−9
(−23) 		10
(−12) 		25
(−4) 		37
(3) 		39
(4) 		53
(12) 		55
(13) 		36
(2) 		28
(−2) 		3
(−16) 		0
(−18) 		−9
(−23)
Average precipitation inches (mm) 4.59
(117) 		4.55
(116) 		4.68
(119) 		3.81
(97) 		3.56
(90) 		4.54
(115) 		4.75
(121) 		4.30
(109) 		3.82
(97) 		3.28
(83) 		3.98
(101) 		4.57
(116) 		50.43
(1,281)
Average snowfall inches (cm) 1.0
(2.5) 		0.4
(1.0) 		0.4
(1.0) 		0.0
(0.0) 		0.0
(0.0) 		0.0
(0.0) 		0.0
(0.0) 		0.0
(0.0) 		0.0
(0.0) 		0.0
(0.0) 		0.0
(0.0) 		0.4
(1.0) 		2.2
(5.6)
Average precipitation days (≥ 0.01 in) 11.1 10.4 10.5 8.9 9.4 11.1 12.0 10.2 7.3 6.8 7.9 10.7 116.3
Average snowy days (≥ 0.01 in) 0.7 0.3 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4 1.5
Average
relative humidity
(%) 		67.6 63.4 62.4 61.0 67.2 69.8 74.4 74.8 73.9 68.5 68.1 68.4 68.3
Average dew point °F (°C) 29.3
(−1.5) 		30.9
(−0.6) 		38.5
(3.6) 		45.7
(7.6) 		56.1
(13.4) 		63.7
(17.6) 		67.8
(19.9) 		67.5
(19.7) 		62.1
(16.7) 		49.6
(9.8) 		41.0
(5.0) 		33.1
(0.6) 		48.8
(9.3)
Mean monthly sunshine hours 164.0 171.7 220.5 261.2 288.6 284.8 273.8 258.6 227.5 238.5 185.1 164.0 2,738.3
Percent possible sunshine 52 56 59 67 67 66 63 62 61 68 59 53 62
Average ultraviolet index 2.8 4.1 6.1 7.9 9.1 9.7 9.9 9.2 7.4 5.2 3.3 2.5 6.4
Source 1:
NOAA (relative humidity, dew point and sun 1961–1990)[12][6][13]
Source 2: UV Index Today (1995 to 2022)[14]

See or edit raw graph data.

Effect on vegetation

Some palm trees like

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

severe thunderstorms and tornadoes, with the cool air acting like a fire extinguisher to the storms.[citation needed] 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

clear and calm nights, particularly when the humidity is low. Peachtree City and especially Newnan often report dramatically lower temperatures (by as much as 4 °C or 7.2 °F) 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

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 70 miles per hour (113 km/h; 31 m/s) officially at Marietta.[15]

Such events are very rare so far inland, some 250 miles (400 km) inland from the

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

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

Cabbagetown, and Fulton Bag and Cotton Mills to the east. While there were dozens of injuries, only one fatality was reported.[17] City officials warned it could take months to clear the devastation left by the tornado.[18]

Winter storms

The area experiences a

La Niña developing the following summer, additional 1.2 inches (3.0 cm) 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 1.6 inches (4.1 cm) in 1881, and 0.3 inches (0.8 cm) in 1882. A trace last fell on Christmas
in 1993, and a dozen other years before that.

A blizzard (see: 1993 Storm of the Century) caught much of the Southeast off-guard in 1993, dumping 4.5 inches (11.4 cm) at the Atlanta airport on March 13, and much more than that in the suburbs to the north and west, as well as in the mountains. Dallas, a suburb about 30 miles or 48 kilometres to the west-northwest, received 17.5 inches (44.5 cm) from the storm. Some people were awakened by thunder and lightning in a very rare thundersnow event. Several areas of northern Cobb County recorded over 15 inches (38 cm) in snowdrifts. It is widely regarded as the snow event of the century for Atlanta, and is referred to as the "Storm of the Century", placing fifth in the city's snowfall records. The only other recorded winter storm of comparable severity was the Great Blizzard of 1899, which struck in February. A blizzard hit on January 9–15 crippling the city and leaving schools out for the whole week. Ice-covered roads and over eight inches of snow fell in some places with over a foot in the far northern metropolitan area.

The heaviest snow, however, was on January 23, 1940, when 8.3 inches (21.1 cm) buried the city during its second-coldest month on record.

Thanksgiving
on record.

Prior to March 2009, the most recent major snow occurred at the beginning of 2002, when up to 3 inches (7.6 cm) fell on January 2–3. As of 2007, the stretch of five nearly or entirely snowless winters made for an extremely long period compared to average. This streak was ended in January 2008 when 0.4 inches (1.0 cm) fell on January 16 and 1 inch (2.5 cm) fell three days later. The following year, the first widespread

upper-level low from the Great Plains, while most major storms in the area occur with a typical surface low-pressure area traveling along the Gulf
coast. The 2009 snow tied with the 1993 blizzard and another storm for fifth-heaviest official daily snow in the city's recorded weather history.

Areas to the due east and west often receive more snow than metro Atlanta, because the energy begins to transfer to a coastal low in the Atlantic, on its way to becoming a nor'easter. Also the mountains to the northwest entrap shallow cold air. Average annual snowfall from 1971 to 2000 in Atlanta is 2.9 inches (7.4 cm) – the snowiest month is January with 0.9 inches (2.3 cm). Due to two record-breaking heavy storms during the averaged period, it is actually March that is statistically second with 0.5 inches (1.3 cm) – cut in half if the heaviest storm is removed. This is followed by February with 0.4 inches (1.0 cm) and December with 0.3 inches (0.8 cm), then November, April, and October averaging a trace each. The latest was April 25, when 1.5 inches (3.8 cm) fell in 1910, also the heaviest for the month, and the latest-ever freeze. Four other April snows have been recorded since 1879, the most recent significant one being April 3, 1987. Flurries occurred in 1993 on the afternoon of Halloween, marking only the third recorded October snow (all of which were an unmeasurable trace).

Although December is just as cold as February and has more days, it receives the least snow of any winter month (roughly once per decade), due to less overall precipitation in the later months of the year compared to the rainier mid and late winter. However, the lowest sun and shortest days of the year mean that what does fall can stay around for days. A mid-December 2000 snow (a record 2.5 inches (6.4 cm) for the month) was followed by very cold weather that left spots of it on the ground in shady areas until

power lines
, leaving some without electricity for days. This was the earliest in the season that the metro area is known to have received so much snow, though long-term official records are only kept at Atlanta proper.

freeway and booking hotels
to capacity, unable to get home to the suburbs.

Despite this well-known experience, the same thing happened in January 2014, when snow expected to hit mainly

school systems needed to decide on whether to cancel school for the day, and even the prior winter weather advisory
should have been enough to cause these cancellations.

Drought

The driest year in Atlanta history was 1954 (31 inches of rain), with 2007 being a close second. The Southeastern U.S. drought of 2006–2008 began with dry weather in 2006, and left area

water systems had already taken such measures.) It was the first time the state had enacted such a ban. Throughout the 3-year drought the Atlanta area occasionally experienced smoke from the wildfires in south Georgia, causing the local air to become dangerous for everyone. The severe record drought
which affected the region starting in late 2006 finally began to abate significantly after heavy fall rains in 2009.

Flooding

The historic drought ended with historic flooding in 2009. The

500-year flood; the National Weather Service stated that chances of that much rain anywhere in the region are 1 in 10,000 years.) Some freeways closed temporarily, and several small bridges and culverts
were ruined and will take months to replace. Many homes in the area were completely destroyed. Occasional heavy rains and flood advisories continued through early February 2010.

Flood events are localized from nearly stationary thunderstorms, or more broadly impacting from slow-moving tropical storm remnants, or sometimes from unusually heavy and persistent winter rains during

El Niño
years. Other droughts have also ended in lesser floods, including in 1989. The flooding has also ended as of 2010.

Environmental issues

carbon-neutral
zone, the first in the United States

In 2007, the American Lung Association ranked Atlanta as having the 13th highest level of particle pollution in the United States.[20] The combination of pollution and pollen levels, and uninsured citizens caused the Asthma and Allergy Foundation of America to name Atlanta as the worst American city for asthma sufferers to live in.[21] However in 2010, all counties in the Atlanta metro area began requiring yearly emissions testing for all motor vehicles, with the exception of antique cars and the three most recent model years.[citation needed]

Bright spots include projects that encourage

carbon-neutral zone in the United States. There, neighborhood merchants, through the Chicago Climate Exchange, directly fund the Valley Wood Carbon Sequestration Project (thousands of acres of forest in rural Georgia).[23][24]

Notes

  1. ^ Mean monthly maxima and minima (i.e. the highest and lowest temperature readings during an entire month or year) calculated based on data at said location from 1991 to 2020.
  2. ^ Official records for Atlanta were kept at the Weather Bureau in downtown from October 1878 to August 1928, and at Hartsfield–Jackson Int'l since September 1928.[11]

References

  1. ^ Champlin, Eric (2016-05-25). "Get high in Atlanta: great high-elevation destinations". The Atlanta Journal-Constitution. Retrieved 2022-08-30.
  2. ^ "Altitudes of Major US Cities". Red Oaks Trading, Ltd. Archived from the original on 11 December 2013. Retrieved 16 October 2017.
  3. ^ Yeazel, Jack (March 23, 2007). "Eastern Continental Divide in Georgia". Archived from the original on 2007-05-29. Retrieved July 5, 2007.
  4. ^ "Florida, Alabama, Georgia water sharing". WaterWebster. Archived from the original (news archive) on 2007-07-20. Retrieved July 5, 2007.
  5. ^ "What is my arborday.org Hardiness Zone?". Arbor Day Foundation. Archived from the original on 2017-12-01.
  6. ^ a b c d e f g h "NowData – NOAA Online Weather Data". National Oceanic and Atmospheric Administration. Retrieved May 4, 2021.
  7. doi:10.1175/1520-0493(1977)105<0553:WACOJ>2.0.CO;2
    .
  8. ^ "Storm of the Century". Our Georgia History. Archived from the original on 2020-07-19. Retrieved 2020-07-18.
  9. Weather.com. Archived from the original
    on August 5, 2007. Retrieved April 2, 2006.
  10. ^ "Climate at a Glance -". National Centers for Environmental Information (NCEI). Retrieved 2022-08-30.
  11. ^ ThreadEx
  12. ^ "Summary of Monthly Normals 1991–2020". National Oceanic and Atmospheric Administration. Archived from the original on May 4, 2021. Retrieved May 4, 2021.
  13. ^ "WMO Climatological Normals of Atlanta/Hartsfield INTL AP, GA". National Oceanic and Atmospheric Administration. Retrieved July 18, 2020.
  14. ^ "Historical UV Index Data - Atlanta, GA". UV Index Today. Retrieved April 20, 2023.
  15. ^ "Weather History for Marietta, GA". Weather Underground. Retrieved 2022-08-30.
  16. ^ "Weather History for Atlanta, GA". Weather Underground. Retrieved 2022-08-30.
  17. Atlanta Journal and Constitution. Archived from the original
    on 2009-03-21.
  18. ^ "Police to Atlantans: If you can, 'stay out of the city'". CNN. March 17, 2008. Retrieved 2022-08-30.
  19. ^ "Atlantans Rub Eyes And See City's Biggest Snow: Populace Paralyzed by White Coat". Atlanta Daily World. January 24, 1940. p. 1.
  20. ^ American Lung Association (2011-05-02). "Half of Americans still affected by dangerous pollution levels". City Mayors. Retrieved 2022-08-30.
  21. ^ DeNoon, Daniel (2007-01-18). "Atlanta Named "Asthma Capital" For 2007". CBS Metro. Retrieved 2022-08-30.
  22. ^ Carl, Terry (November 18, 2005). "EPA Congratulations Atlanta on Smart Growth Success". Environmental Protection Agency. Retrieved April 15, 2008.
  23. ^ Jay, Kate (November 14, 2008), "First Carbon Neutral Zone Created in the United States", Reuters, archived from the original on September 7, 2009
  24. ^ Auchmutey, Jim (January 26, 2009). "Trying on carbon-neutral trend". Atlanta Journal-Constitution. Archived from the original on 2009-03-06.

External links

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