20% Chance of Afternoon Storms
I hope this finds you staying cool through this historic heatwave. How rare is this event? Yesterday, Athens hit a high of 109°F, making it the hottest day in Athens since climate records began. As of 5pm today, Atlanta and Columbus both hit 106°F, both breaking their all-time record highs. Macon sits with a high of 108°F, tying it's all-time record high.
Your Forecast:Tonight: mostly clear skies with a low around 74°F.
Sunday: sunny and hot! High near 106°F. Higher humidities mean heat index values near 109°F.
The Week Ahead: For Sunday afternoon through the rest of the week, we'll introduce a little moisture into the forecast. This means for most of the week, we'll have a slight (20%) chance of isolated thunderstorms in the afternoon. With higher dewpoints, the heat indexes will also be high. It may not be 109°F, but it will still feel hot. The heat wave is not yet over, but we've hit its peak. Temps will slowly begin to lower during the week. By Independence Day, we'll have highs in the upper 90s/lower 100s and drop back down to the mid 90s by next weekend. With heat like this, I wouldn't be surprised if some of the isolated storms reach severe limits.
The Heat Wave: Answers to your questions
What's causing the heat wave? The cause of all the heat is a strong mid-level and upper-level ridge along with surface high pressure. When these ridges of high pressure are stacked as they currently are, surface temperatures can soar. In a high pressure system, air sinks and spreads outward. The sinking and compression of the air causes even warmer temperatures and also keeps the air from rising. No rising air means no convection. That's why we've had no clouds Friday or Saturday to provide some much needed shade.
Why has Athens been hotter than Atlanta? Athens hit 109°F yesterday while Atlanta only made it to 104°F. Why? The current drought conditions have a lot to do with it. During a drought, soil moisture is very low. Typically, some of the Sun's radiant energy is used to evaporate part of this moisture. Scientists call this latent heat. The Sun's energy is stored as latent heat through the phase change to water vapor. You can't feel this latent heat. With little soil moisture during a drought, less of the Sun's energy gets stored as latent heat. Instead this energy heats the ground and the lower atmosphere, causing temperatures to rise. Take a look at the current drought conditions for Georgia. The Atlanta area is in severe drought, while Athens is in extreme drought:
Why was it cooler today than yesterday? Early this morning, the outflow from the remnants of a Mesoscale Convective System moved south from the Carolinas and brought cooler (relatively that is) low level temperatures and winds from the northeast. Places to our south in Central Georgia were warmer than yesterday. Milledgeville sits at 109°F and likely made it to 110°F today.
Safety: Be sure to check on you older friends and relatives. Older age and medications can make the body less capable of cooling properly. Research shows that day 3 and later of high temperatures are very deadly for the elderly and confined animals because high temperatures day after day can take an increased toll on the body. Keep your pets and children inside during the hot daytime hours and NEVER leave them in a hot car. Athens is in an excessive heat warning until 9pm Sunday for heat indexes of 110°F to 113°F. For more information on heat safety, visit: http://www.noaa.gov/features/earthobs_0508/heat.html
Last Night's Derecho
Yesterday afternoon and evening, an incredibly strong derecho moved from the Midwest to the East Coast through Illinois all the way to Virginia, Maryland, and DC. There were over 800 reports of wind damage from the storm and it also knocked out power for millions of people. Many people still have no power (and thus no air conditioning) today as the area experienced sweltering heat. DC issued a state of emergency after the storm due to the numerous trees down. For more information on derechos, visit Matt's recent Earthsky post: http://earthsky.org/earth/what-you-need-to-know-about-derechos
|A composite image from SPC of yesterday's derecho|
Weather Video of the Day:
Today's video is footage of the strong winds from the derecho in Charleston, WV: