Storms

Every survival game has its hazards: lightning, wild storms, nights you'd better be indoors for. Real Earth has those too, and some pack more energy than an atomic bomb. Understanding storms is how people stay alive through them.

A thunderstorm is a storm with lightning and thunder. At any moment, about 2,000 thunderstorms are happening around the world.

They need three ingredients: moisture, unstable air (warm air near the ground with cold air above), and something to lift the air, like a cold front, mountains, or a hot afternoon.

Thunderstorms go through three stages:

1. Cumulus (developing) stage: warm, moist air rises in an updraft, building a tall cumulus cloud.
2. Mature stage: the cloud becomes a towering cumulonimbus. Rain and hail fall, dragging cold air down in a downdraft. Updrafts and downdrafts side by side: this is the most intense stage, with heavy rain, lightning, and sometimes hail.
3. Dissipating stage: downdrafts take over, cutting off the warm air supply, and the storm fizzles out.

The whole life cycle of a single storm cell is usually less than an hour. The strongest, longest-lasting thunderstorms are rotating giants called supercells.

Inside a storm cloud, ice and water bump around and build up electrical charges, negative at the bottom and positive at the top. Lightning is a giant spark that releases that charge, between clouds or between a cloud and the ground.

A lightning bolt heats the air to about 30,000 °C, five times hotter than the surface of the Sun. The air expands so violently it makes a sonic boom: thunder.

Light travels almost instantly, but sound travels about 1 km every 3 seconds (or 1 mile every 5 seconds). Count the seconds between the flash and the boom, divide by 3, and you know about how many kilometers away the strike was.

Safety rule: "When thunder roars, go indoors." If you can hear thunder, you're close enough to be struck. Lightning also starts many of Idaho's wildfires, especially from "dry lightning" in summer storms where the rain evaporates before reaching the ground.

A tornado is a violently spinning column of air reaching from a thunderstorm down to the ground. It's the most violent storm on Earth for its size, with winds that can top 300 mph.

Most strong tornadoes come from supercells. Winds at different heights blowing at different speeds and directions (called wind shear) create a horizontal spinning tube of air. A strong updraft tilts it upright, forming a rotating mesocyclone. A funnel cloud may then drop down; once it touches ground, it's a tornado.

Tornadoes are rated on the Enhanced Fujita (EF) scale from EF0 (minor damage) to EF5 (total destruction), based on the damage they cause.

The U.S. gets more tornadoes than any other country, over 1,000 a year, mostly in Tornado Alley in the Great Plains. Idaho gets only a few small ones a year.

A hurricane is a huge, spinning tropical storm with winds of at least 74 mph. In the western Pacific it's called a typhoon, and in the Indian Ocean a cyclone. Same storm, different names.

Hurricanes form over warm ocean water (at least about 27 °C). Warm, moist air rises, condenses, and releases heat, which powers the storm like an engine. The Coriolis effect gets it spinning.

Parts of a hurricane:

• Eye: the calm, clear center. It can be eerily sunny.
• Eye wall: the ring of the strongest winds and heaviest rain around the eye.
• Rain bands: spiral arms of storms swirling outward.

Hurricanes are rated on the Saffir-Simpson scale from Category 1 (74 mph) to Category 5 (157+ mph). The deadliest danger usually isn't the wind. It's the storm surge, a wall of seawater pushed onshore by the storm. Hurricanes weaken once they move over land or cold water because they lose their fuel.

• Blizzards: heavy blowing snow with winds of at least 35 mph and visibility under a quarter mile for 3 hours or more. Idaho's open plains are famous for whiteout ground blizzards that close I-15.
• Ice storms: freezing rain coats everything in ice, snapping branches and power lines.
• Avalanches: in the mountains, heavy new snow on top of weak layers can break loose and slide downhill at high speed. Avalanches kill about 23 people across the U.S. in an average winter, and Idaho's backcountry is part of that risk. Check the avalanche forecast before heading out.

Storms can cause flash floods, fast floods that hit within minutes or hours of heavy rain, especially in canyons and burn scars. Never drive through floodwater: just 12 inches of moving water can float a car.

The opposite problem is drought, a long period with much less precipitation than normal. Droughts dry out farms, lower rivers and reservoirs, and set up dangerous wildfire seasons.

The National Weather Service issues two kinds of alerts:

• Watch: conditions are right for the hazard to form. Be ready.
• Warning: the hazard is happening or about to happen. Take action now.