Welcome to You Ask Andy

Larry Pungman, age 11, of Winnipeg, Manitoba, Canada for his question:

WHY IS THERE NO LIGHTNING IN THE WINTER?

Lightning comes with tornados and howling hurricanes. But most of it is created in ordinary thunderstorms. In coastal regions these storms tend to build up on sultry summer days. In other regions they occur on summer nights or on winter nights. Weather experts tell us that there are reasons why this is so.

During an average day, about 44,000 thunderstorms occur in various places around the globe. Right now, perhaps 1,800 flashes of lightning are piercing the clouds. All of these dramatic weather events are caused by similar conditions in the atmosphere.


These thunderstorm conditions tend to build up at different seasons in different parts of the world. The scene is set when the air aloft is quite a bit cooler than the air at ground level. Meteorologists call the special situation a steep temperature gradient. When it occurs, the temperature between ground and several miles aloft decreases  at a steady rate.

This particular weather pattern also creates certain variations in air pressure. But the temperature gradient plays the major role in building a thunderstorm. This may occur in winter or summer.

In summer, lofty sea breezes often cool the air high above the scorching ground. This creates the temperature gradient that builds up thunder and lightning on summer afternoons.

In the middle of our continent, there are no cool daytime breezes to cool the air high above the hot ground. However, after sunset, heat escapes from the upper air level, while the surface stays hot. A steep temperature gradient builds up  and stormy lightning occurs around midnight.

Over the oceans, most thunder and lightning storms occur on winter nights. This is because the seas warm up and cool off more slowly than the land. In winter, the water warms the lower air  but the upper air becomes very chilly, especially after dark. `

The difference between the lower and upper air temperatures may be 30 degrees or more. In summer, the ground level may be 90 and the upper level 40 degrees.  In winter over the sea, the lower level may be a coolish 50 and the upper level way below freezing. Either of these conditions can whip up a thunderhead.

 

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