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Currently at Atlanta’s Hartsfield (ATL) |
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The summertime heat in the Southeast can be oppressive, despite the fact that actual air temperatures are relatively mild compared to those of the Great Plains and Midwest. For example, the average high temperature in Atlanta at the climatological peak of summer (i.e., when the average high temperature reaches its annual maximum before gradually dropping toward autumn) is 89º from June 30 through August 13 (based on the current 30-year average using data from 1981 through 2010). On no day during the year does Atlanta’s 30-year averaged high temperature exceed 89ºF. By comparison, DFW’s 30-year averaged daytime high temperature surpasses 90ºF by June 7th and stays above 90º until September 13. Furthermore, the peak summertime temperature at Dallas/Fort Worth is 97º each day from July 25 through August 17 (24 days) — eight degrees warmer than Atlanta’s average annual peak and lasts about two weeks longer.
As of the date of this post (June 21, 2016), Atlanta’s all-time hottest temperature has been 106ºF set on June 30, 2012 (Records began: 10/4/1878). Furthermore, in 136 years of weather records, Atlanta has reached 100 degrees on just 81 days. By comparison, the all-time record high at Dallas/Fort Worth is 113ºF (tied on two consecutive days in 1980: June 26 and June 27). The high temperature at DFW has reached or exceeded 100º on 1,990 days since records at DFW began (20 years later than Atlanta, in 1898).
The following are the criteria used by the NWS in Atlanta, Georgia (FFC) and apply to the entire State of Georgia. Generally, these same criteria apply for most surrounding NWS offices, with only slight variations.
When is a Heat Advisory Issued by the NWS in Atlanta/Peachtree City?
A Heat Advisory may be issued when there is an 80% chance or greater that the following will occur:
- Daytime heat index expected to meet or exceed 105ºF -or-
- Daytime air temperature expected to exceed 103ºF
- Typically issued 12 to 24 hours in advance
When is an Excessive Heat Warning Issued?
An Excessive Heat Warning may be issued when there is an 80% chance or greater that the following will occur::
- Daytime heat index expected to meet or exceed 110ºF -or-
- Daytime air temperature expected to meet or exceed 105ºF
- Typically issued 12 to 24 hours in advance
What is an Excessive Heat Watch?
An Excessive Heat Watch is a precursory product issued when conditions are coming together for dangerous heat in the coming days. For example, let’s suppose dangerous heat may develop 2 days from today, but forecaster confidence isn’t high enough just yet to issue a Warning. As with Winter Storm Watches, an Excessive Heat Watch could be issued to raise awareness to the possibility of dangerous heat that may eventually warrant an upgrade to a Warning.
An Excessive Heat Watch may be issued when there is an 50% or greater chance that the following will occur during the forecast period, up to 3 days in advance:
- Daytime heat index expected to meet or exceed 110ºF -or-
- Daytime air temperature expected to meet or exceed 105ºF
- Typically issued 36 to 72 hours in advance
Recent Changes in Heat Advisory & Heat Warning Criteria
In the past, the criteria also required overnight low temperatures of 75ºF or warmer for two consecutive nights (in addition to the daytime temperature criteria) before an advisory or a warning would be issued. However, the nighttime temperature requirement was eliminated. Also, the duration requirement (i.e., 2 consecutive days) was also eliminated. Therefore, if the conditions above are predicted to occur for just one day, a heat advisory or an excessive heat warning may be issued.
Heat Index Chart, Calculator, and other Tools
Calculator: Check out our heat index calculator and charts.
✏️ Read More: What is the heat index and how is it calculated?
When did Weather Records Begin for Atlanta?
Weather record-keeping began in Atlanta in 1878. The official period of record is 146 years, 2 months and 18 days (10-4-1878 to Present). You can search the weather records for Atlanta and dozens of other Georgia locations using our free database search tool.