Climate Variability

Notice: This is the old website for the State Climate Office and is no longer updated. For our new site, please go to


2.1a  General Circulation of the Atmosphere

Winds circulate around the globe because of the rotation of the earth and the energy from the sun.


2.1b  Ocean Circulations

Much like the earth’s atmosphere, which circulates warm and cold air across the earth, the ocean also circulates warm and cold water across the world.


2.1c  Temperature Gradient

A temperature gradient is the change in temperature across a specified boundary or front.


2.1d  Sea and Land Breezes

Sea and Land Breezes describe the wind that blows onshore from sea to land during the day and blows offshore in the evening.


2.1e  Monsoon Systems

Monsoons are massive, seasonally changing sea breeze circulations that form due to temperature differences between land and ocean.


2.2  Semi-Permanent Highs and Lows

Semi-permanent highs and lows are persistent pressure systems that appear over an area during the year and affect how storms and weather systems enter the United States.


2.3  Mid-Latitude Cyclones

Mid-latitude cyclones are huge weather systems that form from a low pressure system and cover a wide area with precipitation.


2.4  Tropical Cyclones

Tropical Cyclones are powerful storms that develop over the ocean, mostly during the summer months.  The Southeast is affected by tropical storms that form in the Atlantic Ocean and the Gulf of Mexico.


2.5  North Atlantic Oscillation

The North Atlantic Oscillation is a weather phenomenon that affects the jet stream and can alter weather patterns in some parts of the world.


2.6  Pacific/North American Pattern

The Pacific/North American Pattern describes a change from normal in surface temperature and precipitation patterns across the United States.


2.7  El Niño

El Niño is a climate pattern representing an unusual warming of the eastern tropical Pacific Ocean which is linked to impacts on weather and climate patterns around the world.


2.8  La Niña

La Niña is a climate pattern representing the cooling of the eastern tropical Pacific Ocean which impacts weather and climate conditions all over the world.


Southeast Climate Patterns

2.9a  Southeast Temperature

The information below focuses on the changes of temperature the Southeast United States experiences.


2.9b  Southeast Precipitation

The Southeast (as defined here) includes NC, SC, AL, GA, FL, and VA.  The Southeast gets an average of around 50 inches of precipitation each year, including some frozen precipitation in all areas except most of Florida and southern Georgia.


2.9c  Southeast Frosts and Freezes

Frosts form when temperatures are near or below freezing and relative humidity values approach 100% near the ground.  A freeze occurs when the temperature is at or below 32oF throughout the area.  In a freeze, surface temperatures can drop to below 28 degrees, which is the threshold for killing damage for many plants.


Drought and Heat

2.10a  Drought

Drought occurs when sufficient water needed to sustain an area is not available, causing economic impacts on agriculture, society, and ecosystems.  It is most often caused by lack of rainfall over a long time period but can also be affected by unusually high temperatures and dry spells, particularly during summer months.


2.10b  Effects of Drought

Lessened amounts of precipitation over an area for an extended period of time has many effects on farmland and crops. Drought conditions result from a lack of precipitation and this has many effects on the surrounding land and weather conditions. Drought conditions can worsen after prolonged periods of no rainfall, especially in areas where the water supply is short.


2.10c  Heat Waves

Heat waves are extended periods of unusually hot weather that affect human and animal health as well as energy use. 


2.10d  Drought and Wildfires

Wildfires can occur during drought conditions when the land and vegetation have dried out.