Heat Advisories, Watches and Warnings
Another day, another heat advisory. As of Friday, it was the eighth day in a row a heat advisory was issued for most of Central Georgia. Also on Friday, an "Excessive Heat Watch" was issued for Southern parts of Central Georgia. We've been throwing these advisories and watches and warnings out for a while now, but I can't remember if we've ever explained the differences between the heat related ones. So here we go!
The most common one we've seen this summer is the "Heat Advisory" which is issued within 12 hours of the onset of the following conditions: heat index of at least 105°F but less than 115°F for less than 3 hours per day, or nighttime lows above 80°F for 2 consecutive days. Pretty simple.
The newest one is the "Excessive Heat Watch". It is issued by the National Weather Service when heat indices in excess of 105ºF (41ºC) during the day combined with nighttime low temperatures of 80ºF (27ºC) or higher are forecast to occur for two consecutive days. So it basically means that nighttime temperatures and dew points aren't going to drop enough to provide adequate cooling overnight to those of us without the luxury of an air-conditioner. This can create a dangerous situation because the body isn't able to recoup and recover before the heat of the day kicks in again.
Just like a Tornado Watch and Warning, a watch means it's possible for this type of weather to occur while a warning indicates that the event is already occurring or imminent.
The "Excessive Heat Warning" has one caveat... Even if nighttime temperatures dip below 80, the warning will be issued if the heat index goes over 115. This is because the guidance for an "Excessive Heat Warning" is: An Excessive Heat Warning is issued within 12 hours of the onset of the following criteria: heat index of at least 105°F for more than 3 hours per day for 2 consecutive days, or heat index more than 115°F for any period of time.
Hope this clears up a little confusion for you. Stay safe out there this summer!
Meteorologist Jason Disharoon