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FOUR SEASONS BREEZE | JULY 2020 9 By Mel Zeldin As they say, "the good ol' dog days of summer" are here. July and August bring the most continuous hot weather of the year to the inland areas of Southern California. Toward the end of July and into August, the possibility of late afternoon thunderstorms increases. So, let's take a step back and delve into the reasons why we have summer thunderstorms in the first place. Above 10,000 feet, winds generally flow from west to east, and are strongest in the winter months. During the summer, these winds are quite light, allowing for heated air at the ground to rise upward. If moisture is added into the air, the rising air cools and eventually reaches a point where it condenses into cloud droplets, and a cloud begins to form. As long as the air in the cloud remains warmer than the surrounding clear air, the cloud will continue to expand and rise vertically. As the air moves upward, the cloud droplets bump into each other and form a larger droplet. After a while these become big enough to form raindrops. As long as the upward drafts (called "updrafts") are greater than the gravitational downward pull of the raindrops, the raindrops will continue to grow in size. Eventually, the drops reach a larger size where gravity overcomes the updrafts, and the drops begin to fall downward, and this causes downward air movement, called "downdrafts." So, within one part of the cloud, there are updrafts, and in another part of the cloud there are downdrafts. Upward cloud droplets and downward large raindrops bump into each other, creating both positively and negatively charged particles. Positively charged particles are lighter than negative particles, so they accumulate at the top of the cloud, while the negatively charged particles accumulate at the bottom of the cloud. Now, if you've ever shuffled across a carpet and then touched something metal, you might get a slight spark of static electricity. That's because your movement across the carpet created an accumulation of negative electrons which moved through your body and discharged into the metal. There are many other common situations which cause this. I'm sure most of you at some time in your life have experienced that static electricity zap. What happens in the cloud is very similar, but on a hugely larger scale. Eventually, the negative particles at the bottom of the cloud discharge within the cloud to the positives at the top, and we have in-cloud lightning. Sometimes, there are accumulations of positive particles at the ground which now tend to move upward toward the negative charge at the bottom of the cloud. In these circumstances, the cloud discharges toward the ground and eventually connects with a positive accumulation moving upward from the ground. When they connect, we have a cloud-to-ground lightning bolt. The lightning bolt is incredibly hot, as much as five times hotter than the surface of the sun. The air around the bolt is heated tremendously and creates a shockwave as the air expands and compresses the surrounding air. This action creates the cracking sound associated with the lightning bolt. The air then cools rapidly and vibrates as it moves back into place creating the rumbling sound following the lightning flash. Since light moves much faster than sound, we see the lightning flash before we hear the thunder. The farther away the storm is, the longer the lag time between lightning and thunder. So why do we occasionally have summer thunderstorms here in Beaumont? The key is moisture. The air is typically too dry to cause thunderstorm clouds to form. But occasionally we do get some moisture. You might think it comes from the vast Pacific Ocean to our west, since we're so close to such a large moisture source. But in fact, the moisture typically comes from Mexico to the southeast which draws much of its moisture from the Gulf of Mexico and the subtropical Pacific Ocean. Atmospheric wind patterns in the summer move that moisture into Arizona and New Mexico, and is typically called their "monsoon season." Sometimes the moisture is farther west into the Coachella Valley. Because updrafts are enhanced by flowing up the nearby mountain slopes, the clouds often form initially over the mountain tops. Once the clouds build enough height to cause thunderstorms, the air flow can move these thunderstorm "cells" off the mountain tops and into the San Gorgonio Pass area. Thunderstorms are enjoyable to watch. Late afternoon activity with the sun setting to the west can produce beautiful rainbows and cloud colorations. If you do go outside during one of these events, just be careful about the lightning. If the thunder is heard less than five seconds after you see a lightning flash, the cell is less than a mile from you. Stay inside if that is the case. If you have a question about any weather topic, please feel free to e-mail me at mzeldin45@gmail.com. Periodically, I will devote a column to answer your questions. Why We Have Thunderstorms

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