Why is lightning more common during the summer?
Most of the world is lightning flashes from glowering thunderheads, But streaks of lightning also flash from certain regions of the howling hurricane and sometimes there is lightning in a furious little tornado. In the temperate land regions, we get most of our thunderstorms, hence most of our lightning, during the summer months.
An electric storm, complete with pealing thunder and flashing lightning, can build up when weather conditions are just right. There must be two distinct and contrasting layers of air above the ground. The lower layer of air, nearest the earth, must be light arid rising in an upward current. The layer of air above it must be very much cooler and heavier.
The weather conditions necessary for a thunderstorm must change in a line from the earth to several miles above the surface. The major variation is in temperature. An electric storm can build up only when there is a steep temperature gradient with the warmest air near the earth and very, very much cooler air above it.
On a summer day, the sun pours down on New England and haw York. The scorching ground warms the air above it to perhaps 90 degrees. But this warm layer of lower air does not pass its heat on to the air above it. It expands and rises and as it does this it tends to coo::. itself. The breezes blowing two or three miles above the ground may be below freezing point and the warm air below has no heat to give them.
This steep temperature gradient is just the right weather condition to start a thunderstorm. Electricity builds up in the turbulent winds of the thunderhead and from time to time this is discharged in flashes of lightning. Meantime, in the mid. western states, other weather conditions keep the cool breezes above at bay until after sunset.
Then the contrast of temperatures upstairs builds up to form a summer mid night thunderstorm.
Over the ocean, most of the thunderstorms occur during the winter nights. The ocean holds its summer heat much longer than the land, often far into the winter. The warmish water warms the layer of air above it. After sunset, the higher layers of air lose their heat fast. The lower air may be cold in terms of weather temperature, but the higher air is much, much colder. Here again we have the steep temperature gradient necessary for thunderstorms and lightning.
Around the world, about 44,000 thunderstorms occur every day. In some places, these storms occur most often on hot, summer afternoons. But other places expect them, during the summer nights and some places get most of their thunderstorms during winter nights. At any moment throughout the year, about 3,800 storms are occuring at various points around the world.