Weather + Climate

 

Last Update: 15 May 2018

Monthly weather and climate data can be found here for the State of Georgia and the City of Atlanta. Quick data points and rankings are posted on the right side of the homepage (below posts for mobile users). All data is pulled from the National Oceanic and Atmospheric Administration (NOAA) websites and is updated on a daily and monthly basis. Georgia temperature data and drought data for the previous month is released by NOAA several days into the new month (ex: January data is released around Feb 7th).

 

Current Conditions

Below is the same chart that appears to the right (desktop) or below the article (mobile). All data is updated on an hourly basis. The average temperature is simply the high for the day minus the low for the day, divided by two. The furthest data point from the left is the month-to-date average temperature deviation. This is the difference between the average temperature so far this month and the normal average temperature up to this point in the month. That number is then compared to its corresponding number for all years going back to 1930 to determine how warm or cold it has been up to this point in the month compared to previous years. Since our graph updates on an hourly basis, the temperature deviation will change throughout the day, which means the ranking could change throughout the day. Slide 2 on the right (desktop) or below (mobile) shows the final average temperature deviation and ranking for the previous month. Slides 3 and 4 show the same information for Georgia and the continental U.S.

The chart with the blue temperature values on the right (desktop) or below (mobile) shows the minimum average temperature needed today for the current month to be the 1st warmest on record. It also shows the maximum average temperature needed today for the current month to be the 1st coldest on record. This provides some perspective into how warm or cool temperatures have been up to this point in the month – for instance, in order to undo the warmth we’ve seen between May 1 and May 20, the average temperature on May 21 would have to be -193°F to make May 1- May 21 the coldest such period on record, but would only have to be 69°F to make it the warmest such period on record.


State of Georgia Average Temperature

The figure below shows the average temperature up to that point in the year for the State of Georgia versus the historical 20th Century Average for that time period. Average daily temperatures are calculated by adding the high temperature to the low temperature and dividing by two. All the daily average temperatures are then used to determine the monthly average temperature.

NOAA has provided a ranking tool to put the data into historical context. Using 123 years of recorded data, the tool shows you how data for a particular time period compares to historical data for that time period.

The chart below uses the Year-to-Date feature to show how warm or cool the year has been up to that point compared to previous years up to that point. For example, the average temperature in Georgia from January 1, 2017 to February 28, 2017 was 54.8ºF (orange bar). Historically, the average temperature during that period is 47.4 °F (black line). This is a departure from the historical average of +7.4 °F. In 123 years of record keeping, January 1, 2017 to February 28, 2017 was the 3rd warmest such time period of any year.

 

April Analysis

April temperatures throughout Georgia were 2.4°F below the 20th Century average. This pushed the year-to-date temperature to 0.9°F above average, which makes Jan 1, 2018 to April 31, 2018 the 79th warmest such period on record. So far 2018 has been the opposite of 2017: the beginning of last year was very warm while January, March, and April of 2018 all saw temperatures below average. Despite temperatures in three of the four months this year being below average, our 2018 year-to-date temperature is 0.9°F above average because February’s temperatures were about 10°F above average.


City of Atlanta Average Temperature

The figure below shows the actual average monthly temperatures at Atlanta Hartsfield International Airport versus the normal average monthly temperatures. The numbers above each bar represent the difference between the actual average monthly temperature the normal average monthly temperature. For example, in April 2017 the actual average monthly temperature was 67.8 °F and the normal average monthly temperature was 62.0°F. The average temperature was therefore 5.8°F above normal. The Year-to-Date is the average of the actual and normal monthly temperatures from January 1st to the end of the previous month. All data is from the National Weather Service Forecast Office in Peachtree City, GA.


April Analysis

April temperatures in Atlanta were 2.3°F below average. Temperatures were consistently below average throughout the month, though we saw no records (April 17th came within 1°F of tying the record low, see below). Due to February’s temperatures being 10°F above average, the year-to-date average temperature in Atlanta is still about 1°F above normal.


 Atlanta Average Precipitation

The chart below shows the actual monthly precipitation recorded at Atlanta Hartsfield International Airport (blue bar) versus the average monthly precipitation (blue line).  All data is from the National Weather Service Forecast Office in Peachtree City, GA.

April Analysis

Prior to April 23rd we were on our way to a dry month. However, on April 23rd we saw record rainfall with Atlanta recording over 4 inches of rain. Thanks to that very wet day, Atlanta saw a surplus of 3 inches of rain in April. So far, we are about 4 inches above normal rainfall level for 2018.


Drought Conditions

The Palmer Drought Severity Index (PDSI) is a widely used model designed to predict drought conditions. The PDSI has its advantages and disadvantages, but NOAA and state and local governments use it to assess drought conditions over time. Negative numbers correspond to drier conditions while positive numbers correspond to wetter conditions. A PDSI value of -4.0 or below corresponds to extreme drought conditions.

Each state is divided into climate divisions with Georgia having nine division. They are numbered from northwest to southeast; metro Atlanta is in District 2 (second from top left) as is Lake Lanier, one of the state’s most important reservoirs. Drought conditions both upstream and downstream of Lake Lanier will influence the reservoir’s water levels. Drier conditions in District 2 and 3 will result in less water flowing into Lake Lanier while wetter conditions in south Georgia and Florida can result in less water being released from Lake Lanier. Tensions in the water wars between Georgia, Florida, and Alabama escalate as drier conditions increase in the southeast region. Below is a GIF of PDSI values for every climate division the country.

April Analysis

Thanks to a wetter-than-normal April, drought conditions in District 3 (NE corner of GA) have subsided. Moderate drought conditions remain in Districts 6 and 9. Out in the west, the recurring summer drought conditions are re-appearing in California, Arizona, and New Mexico.

 


 

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