Georgia's Climate

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Georgia's Climate
Past, Present and Future

• Produced by Pam Knox, Georgia Assistant State
  Climatologist

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What is climate?

• A measure of the general environmental conditions
  and their variability over time and space
• Commonly described by temperature, precipitation,
  wind, humidity and other weather-related factors
• Includes averages, extremes and variability

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What controls Georgias climates?

• Where we are on the globe
• Where we are on the continent
• Landforms and water
• Local conditions

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Georgias position on earth

• Latitude 30-35 N

Our position means that we experience winter in
December, January and February, and summer in
June, July and August, with transitional seasons
in between, due to the suns position in the sky
relative to earth.
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Earth and sun positions at different seasons
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Where we are on the continent

• In mid-latitudes, prevailing wind is from the
  west
• Climate is directly affected by what is upwind
• In Georgia, prevailing wind varies with the
  season, so influences of climate also change

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Georgia is in the southeastern US
Winds in winter tend to be from the NW from over
the continent
Winds in summer tend to be from the SW from the
Gulf of Mexico
Local conditions can affect the prevailing wind
at any location!
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Landforms and water

• Variations in elevation cause variability in both
  temperature and precipitation
• The presence of water or mountains can create
  local circulations which affect local climate

Ground fog in low-lying area
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Landforms of Georgia
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Local conditions

• Vegetation type and land cover can also affect
  climate
• The presence of cities, irrigated land, or other
  human-induced changes can affect local
  conditions, too

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This false-color LANDSAT image shows the
variation of land uses across the state. Dark
greenmountain forests Whitecropland Redcoastal
forests Bright green coastal estuaries
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What does Georgias climate look like?

• Temperature
• Growing season
• Precipitation
• Wind
• Hazards

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Temperature
Annual mean temperature ranges from about 54 F
in the northeast to 68º F in the south.
55
60
65
70
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Temperature
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January mean temperature ranges from about 36º F
in the north to 53º F in the south.
40
50
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Temperature
July mean temperature ranges from about 70º F
along the NC border to 84º F in the south.
70
80
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Temperature
Statewide monthly temperatures vary smoothly from
January (44.7º F) to July (79.5º F) and lag the
seasonal solar radiation by about a month.
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Temperature
Mean extreme high temperatures range from below
90º F in the northeast mountains to over 100º F
in the coastal plain away from the coast.
90
95
100
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Temperature
Mean extreme low temperatures range from below 0º
F in the northeast mountains to over 20º F near
the ocean.
0
x
10
20
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Temperature
The average number of days with temperatures
above 90º F ranges from less than 15 in the
northeast to over 90 in the south.
lt1
15
30
45
x
60
90
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Temperature
The average number of days with temperatures
below 32º F ranges from less than 30 along the
coast to over 120 in a few isolated areas in the
northeast mountains.
120
90
x
60
30
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Temperature Records
Highest temperature was 112º F Louisville 7/24/1
952 Greenville 8/20/1983 Lowest temperature was
17º F CCC Camp F-16 1/27/1940 (in northwest
Georgia)
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Growing season
The median length of the growing season (based on
32º F) ranges from over 270 days along the
southern coast to less than 180 days in the
mountains.
180
x
240
270
300
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Growing season
The average date of last spring frost ranges from
late February along the coast to early May for
the mountains.
May 1
Apr 15
x
Apr 1
Mar 1
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Growing season
The average date of first fall frost ranges from
early October in the northeast to early December
along the southern coast.
Oct 1
Oct 15
Nov 1
x
Nov 15
Dec 1
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Precipitation
The average annual rainfall in Georgia ranges
from a low of about 45 inches near Mt. Vernon in
Montgomery County (X) to a high of over 80 inches
in isolated mountainous areas in the northeast.
70
50
X
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Precipitation
The average annual snowfall for most of the state
is less than 3 inches (green area). The far
south does not usually experience snow. A few
mountaintops in the northeast have more than a
foot of snow each year.
12
3
x
0
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Precipitation
The average monthly precipitation ranges
from 3.4 inches in November and April to 5.3
inches in July.
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Precipitation Records
24 hour rainfall 21.10 inches Americus 7/5-6/199
4 (Tropical Storm Alberto) Calendar year
precipitation 122.16 inches Flat Top 1959 24
hour snowfall 19.3 inches Cedartown 3/2-3/1942
Seasonal snowfall 39.0 inches Diamond 1894-95
.
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Wind
Prevailing winds change across the state from
season to season. Average monthly wind speeds
range from 5 to 9 mph.
Jan
Apr
White 5 mph Light gray 6 mph Dark gray 7
mph Violet8 mph Turquoise 9 mph
Jul
Oct
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Natural Hazards
In the period from 1950-1995, Georgia
experienced an average of 20 tornadoes per year,
of which 6 were strong or violent
tornadoes. Note that tornado reports are
strongly biased by population, so cities tend to
be over-reported compared to rural areas.
x
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Natural Hazards
The Gainesville tornado of April 6, 1936, was
one of the countrys deadliest, with 203 killed
and about 1600 injured.
Photo from Carl Vinson Institute of Government
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Natural Hazards
In the period from 1980-1995, Georgia
experienced an average of 65 hail reports per
year for hail larger than ¾ inch. Hail reports,
like tornado reports, are strongly biased by
population, so cities tend to be over-reported
compared to rural areas.
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Natural Hazards
The number of days with thunder ranges from over
70 per year in the far southwest to about 40
near the northeast border with South Carolina.
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40
50
60
70
3
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Natural Hazards
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The number of days with heavy fog (visibility of
less than ¼ mile) ranges from about 20 in west
central Georgia to over 35 in the NE mountains.
35
30
25
20
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Natural Hazards
Hurricanes occasionally move across Georgia,
although they are usually downgraded to a
tropical storm by the time they enter the state.
This map only shows storms that reached
hurricane force at some point.
Dark RedStrong Huricane. Red Weak
Hurricane YellowTropical Storm GreenTropical
Depression BlackTropical Low
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Climate variability
Georgias climate varies on many different time
scales, from seasonal to multi-decadal. These
variations are due to a number of factors,
including ocean temperatures, land use
changes, and weather and climate events happening
elsewhere in the US and the world.
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Climate variability
One factor that can cause climate to vary is El
Niño. El Niño is one phase of an oscillation in
ocean temperatures and atmospheric pressure in
the eastern Pacific Ocean that can steer weather
systems in the southeastern US and elsewhere. El
Niño is considered the warm phase of the
oscillation. However, El Niño tends to affect
Southern Georgia in winter more than any other
part of Georgia or any other season. La Niña
(sometimes known as El Viejo) is the opposite
atmospheric pattern from El Niño.
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Climate variability
In an El Niño winter, the average precipitation
in the southern half of Georgia is about 2 inches
above the precipitation expected in a neutral
year. In a La Niña year, precipitation is about
2 inches lower than in a neutral year. Northern
Georgia does not show this statistical
relationship. However, there is quite a bit of
variability from one event to the next.
GreenSouth Central RedNorth Central
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Georgias past climate
During the last Ice Age, Georgia probably
experienced a climate somewhat wetter and cooler
than we have today. Models indicate that the
average annual rainfall was about 63 inches and
the annual average temperature was 56.3º F,
compared with modern values of 51 inches and
63.5º F.
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Georgia climate trends
Since 1895, Georgias climate has cooled
slightly (black line on chart). This may be due
to reforestation of Georgia over the last
century or for other reasons. However, the
current trend (since 1965) is toward warmer
temperatures.
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Georgia climate trends
Since 1895, Georgias rainfall has varied from
one year to the next, but there is only a very
slight trend towards higher precipitation over
the last century.
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Thank You!
We hope that you have enjoyed this look at
Georgias climate. If you have questions or
comments, please feel free to contact us
at Climate_at_engr.uga.edu Or visit our web site
at http//climate.engr.uga.edu
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Credits
Many of the charts in this presentation were
obtained from the Climate Atlas of the United
States, published by the National Climatic Data
Center, NOAA, in September 2000 on CD-ROM. You
can access their web site at www.ncdc.noaa.gov