How Do Thunderstorms Cause Hail and Flash Floods?
Strong updrafts carry ice seeds high into a storm, where supercooled water freezes onto them until they fall as hail. Flash floods happen when heavy rain falls faster than the ground can absorb it, often from storms that stall or repeatedly cross the same spot. Both can turn deadly fast.
This unit covers two storm hazards that get less hype than tornadoes and deserve more respect. Hail can wreck a car in minutes. Flooding kills more Americans than tornadoes in most years. You'll learn how each one happens and how to read the warning signs on radar.
What You’ll Learn
- The three ingredients every hailstone needs.
- Why hailstones have clear and milky layers.
- How updraft strength limits hail size, and the official hail size chart.
- The difference between flash floods and river floods.
- How training and backbuilding storms pile up rain.
- Why 12 inches of moving water can carry away most cars.
Lessons In This Unit
- 9.1How Hail GrowsHail forms inside strong thunderstorms. Updrafts carry a small seed, usually graupel or a frozen raindrop, high into the storm where supercooled water droplets freeze onto it...Intermediate · 9 min
- 9.2Flash Floods And River FloodsA flash flood is a rapid rise of water, usually within six hours of heavy rain and often within minutes. It hits small streams, dry washes, city streets and underpasses. River...Intermediate · 9 min
Questions People Ask
What size hail is severe?
Hail 1 inch (quarter size) or larger meets the US severe thunderstorm criterion.
Why are flash floods so dangerous?
Water rises within minutes to hours, and more than half of US flood deaths happen in vehicles driven into flooded roads.
Can it hail in summer?
Yes. Hail forms high in thunderstorms where it is below freezing, even on hot days.
Stay inside for the hail, and turn around for the water. — Jen
