by David Murphy
The short answer: late July or early August. This might not make sense to some people. After all, shouldn't the hottest time of year be in late June during the Summer Solstice, when the sun is at its highest angle above the horizon and the hours of sunlight per day are the longest? In fact, it's true that the earth's surface absorbs more and more solar energy as we move toward the Solstice through April, May and June. It's also true that by late June, after the Solstice is over, the daylight hours begin to shorten and less energy from the sun is being sent earthward. But here's the problem: the earth is still holding on to most of that solar energy it received earlier in the summer as the Solstice passes and cannot radiate or lose all of it at once. It takes solid surfaces like rock, dirt and sand, several weeks to get rid of the excess heat stored up over the previous months. As a result, there's what's known as a lag time between the Solstice and the days when we usually see the hottest average air temperatures.
In most years, these hottest highs occur toward the end of July and the very beginning of August, as that extra stored-up heat is gradually released.