**HEAT INDEX 105 TO 110**
Over the next 24 hours, the ridge of high pressure over the SE US will begin to move westward. The problem is, with the high pressure to our west, the flow will come out of the NW, bringing drier air aloft back into Alabama, reducing afternoon storms and clouds by the weekend.
The atmosphere is in balance over the whole earth between incoming solar radiation heating it up and outgoing longwave radiation cooling it down. However, in the summer, especially in the south, the sun is at a high angle and the nights are short, so the net radiation is almost always positive. So, if air just moves around the central and southern United States, without any cooling influences like clouds, rain, or cooler air moving in, it will slowly get hotter. The 24 hour loop below shows the net radiative flux (incoming solar minus outgoing thermal).
If you add it up over a 24 hour period for Alabama, there is a net energy gain of 125 Watts per square meter this time of year.
So, once the clouds and scattered storms move out by Friday and Saturday, it will start heating up. The scattered thunderstorms lately have added some moisture to the ground, so some of the incoming sun energy will be used to evaporate the water. However, that will increase the humidity and cause the heat index to be higher for a given temperature.
It looks like the hottest weather will stay just SW of us, with highs over 105 possible by Monday in southern Mississippi and Louisiana. However, temperatures will reach the mid to upper 90s Saturday through Monday in Alabama, with some locations likely reaching 100 or 101. Add that to higher humidity than we saw in the last hot summer we had (2007), and heat index readings may approach 110 degrees in many spots.
In any event, if you have outdoor activities planned for the weekend or next week, take precautions for extreme heat. Drink plenty of water (even if you’re not thirsty), limit time outdoors and especially in the sun, and try to schedule outdoor activities (yard work, football practices, band practices, etc.) to early morning before 11 am or evening after 7 pm. Use common sense. Heat-related illnesses start to become a problem when the heat index gets this high. The only relief will be isolated afternoon showers, and by early next week those may be limited.
Remember, also, that summer forecasting of temperatures is difficult around here, so this could change. I want everyone to have a heads up about the possibility.
