Lightning

Lightning is formed inside thunderstorms when electrical charges build up inside a large storm cloud called a cumulonimbus cloud. These clouds are tall and powerful, with strong updrafts (rising air) and downdrafts (sinking air) that help create the conditions needed for lightning.

Inside the cloud, different types of particles exist at different heights. Frozen particles, such as ice crystals and small hail, are found near the top of the cloud, where temperatures are very cold. As these frozen particles collide, they tend to lose electrons so they become positively charged. Near the bottom of the cloud, where temperatures are warmer, liquid water droplets and heavier particles tend to collect electrons, and become negatively charged.

This separation of charges creates a strong electrical imbalance within the cloud. As the difference in charge grows larger, the air between them can no longer block the flow of electricity. When the charge is released, a sudden electrical discharge occurs—this is lightning. Lightning can happen within the cloud (intracloud lightning), between clouds (cloud to cloud lightning), or between the cloud and the ground (cloud to ground lightning). 

Thunder

Thunder is the sound produced by lightning during a thunderstorm. Even though we see lightning first, thunder happens at the same time—the sound just takes longer to reach our ears.

When lightning strikes, it heats the surrounding air to extremely high temperatures in a fraction of a second. This sudden heating causes the air to expand rapidly. As the hot air quickly expands and then cools, it creates a powerful shock wave that moves outward through the atmosphere. We hear this shock wave as thunder.

The sound of thunder can vary. A sharp crack usually comes from nearby lightning, while a long rumble often means the lightning is farther away. This happens because sound travels much slower than light and because the sound waves bounce off clouds and the ground. 

When and Where Tornadoes Occur

Tornadoes can happen almost anywhere, but they are most common in the central United States, an area known as Tornado Alley. They occur most often in spring and early summer, when warm and cold air masses frequently collide. 

The Plainfield, IL Tornado (1990)

The Plainfield tornado was one of the deadliest tornadoes in Illinois history. It struck on August 28, 1990, impacting Plainfield, Crest Hill, Joliet, and surrounding areas.

What Made This Tornado Unusual

• It formed during the afternoon, not the typical late afternoon or evening peak.

• Weather conditions did not look especially severe to many forecasters at the time.

• The storm produced little lightning and rain, making it harder to recognize as dangerous.

Strength and Path

• Rated F5 on the Fujita Scale (the highest rating at the time)

• Winds were estimated to exceed 260 mph

• Traveled about 16 miles

• At times, it moved forward at over 50 mph

Why It Was So Deadly

• No tornado warning was issued before it struck

• Many people were at work or school and had little time to react

• The tornado hit populated areas directly, including neighborhoods, businesses, and schools—including Plainfield High School

Impact

• 29 people were killed

• Over 350 people were injured

• Hundreds of homes and buildings were destroyed or severely damaged

• Plainfield High School and several elementary schools were heavily damaged

Why There Was No Warning

At the time:

• Weather radar technology was less advanced

• Meteorologists relied mainly on visual reports

• The tornado formed quickly and was hard to detect on radar

The Plainfield tornado became a turning point in weather forecasting. After this event:

• Doppler radar use expanded

• Tornado warning procedures improved

• Meteorologists became better at recognizing dangerous but subtle storm signatures 

Click Here to Learn more about the Plainfield Tornado

How Hurricanes Form

Hurricanes begin as clusters of thunderstorms over warm ocean water (at least 80°F). Warm, moist air rises from the ocean surface, and cooler air sinks around it. As more warm air rises, the storm grows stronger and begins to rotate due to Earth’s rotation. 

Hurricanes start small and grow stronger over time. Scientists classify them in stages: tropical depression → tropical storm → hurricane.  A tropical depression has wind speeds less than 39 miles per hour.  If the winds reach speeds between 39-73 miles per hour, the tropical depression becomes a tropical storm.  If it strengthens further, and the winds increase to at least 74 miles per hour, it is considered to be a hurricane. 

Most people think that it is the high winds during a hurricane that is most damaging, but actually it is the storm surge. The ocean floor where the hurricane makes landfall plays a big role in the height of a storm surge. If the water near the coast is shallow, the hurricane pushes more water onto the shore. If the water drops off quickly into deep ocean, the surge is usually lower and less flooding occurs on land. 

When and Where Hurricanes Occur

Hurricanes form over tropical oceans, especially in the Atlantic Ocean, Gulf of America, and eastern Pacific. Hurricane season in the Atlantic runs from June 1 to November 30, with peak activity in late summer, when ocean water is at its warmest.

Even though the waters along the equator are usually the warmest on Earth, hurricanes will not form here.  This is because there is no Coriolis Effect along the equator, therefore, there can be no rotation to form a hurricane.  Hurricanes usually form between 5 and 20 degrees latitude north and south of the equator. 

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