The State of Georgia's Climate

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The State of Georgia's Climate
Georgia Air Quality and Climate Summit 2006

• 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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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

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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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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
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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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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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 monthly precipitation ranges
from 3.4 inches in November and April to 5.3
inches in July.
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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
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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Climate variability
Climate can vary in a variety of ways, including
periodic changes, abrupt steps, and changing
variability around a constant mean.
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Climate variability
What looks like a simple linear trend can
actually be one of a variety of different changes.
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Climate variability
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Climate variability
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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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Coming soon The Georgia Mesonet!
Goal To have automated weather observing
stations spaced across the state at intervals of
about 20 miles reporting real-time weather
information online. This is a cooperative network
which includes the National Weather Service,
USGS, Georgia Environmental Protection Division,
Georgia Forestry Commission, University of
Georgia and other groups. Variables measured
Temperature and precipitation at first, then
wind, soil temperature and possibly other
variables to be added later.
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Coming soon The Georgia Mesonet!
Current Status So far 224 sites have been
surveyed and about 60 chosen to recommend for
inclusion into the Mesonet. Communications have
been tested and are operating at 3 sites and are
about to be tested at about 10 additional sites.
Surveying will continue this summer in central
and northern Georgia.
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Thank You!
If you have questions or comments, please feel
free to contact us at Climate_at_engr.uga.edu Phone
number 706-542-6067 Or visit our web site
at http//climate.engr.uga.edu