How lightning is made
Inside a tall thundercloud, strong currents of air toss water droplets, ice crystals and soft hail up and down. As they crash into each other, electric charge is rubbed off and separated, much as a balloon picks up charge when rubbed on a jumper. The top of the cloud becomes positively charged and the bottom negatively charged, until the difference is so great that a giant spark leaps between them, or down to the ground. That spark is LIGHTNING, and it heats the air around it to around 30,000°C, about five times hotter than the surface of the Sun.
The heated air expands so suddenly that it makes a shock wave, which we hear as THUNDER. Light arrives almost instantly, but sound travels about a kilometre every three seconds, so counting the seconds between the flash and the rumble tells you how far away the STORM is. An American park ranger, Roy Sullivan, was struck by lightning seven times and survived every one.
The man who invented the forecast
Robert FitzRoy, who had captained the ship that carried Charles Darwin around the world, became head of a new British weather office in 1854. After a great storm in 1859 wrecked the steamship Royal Charter and many other vessels, he collected reports by telegraph from around the coast and in 1861 began publishing daily predictions in The Times newspaper. He called them forecasts, a word he chose because he thought prophecy sounded unscientific. He also set up storm warnings for ports, which saved many sailors' lives.
Storms, snowflakes and extremes
A HURRICANE, a typhoon and a CYCLONE are the same kind of storm: a huge spinning system that forms over warm tropical seas. The name depends on the ocean: hurricane in the Atlantic, typhoon in the north-west Pacific and cyclone around India and Australia. The calm centre, the eye, can be tens of kilometres wide, surrounded by the fiercest winds. Storms are given names from lists that rotate every few years, and the names of especially deadly ones are retired so they are never used again.
A TORNADO is much smaller but can have even faster winds, spinning down from a thundercloud to the ground. The largest HAIL ever recorded in the United States, found in South Dakota in 2010, was twenty centimetres across.
In 1885 a farmer in Vermont called Wilson Bentley, nicknamed Snowflake Bentley, became the first person to photograph a single snowflake. He went on to photograph more than 5,000 of them and never found two alike, because each crystal grows along its own path through the cloud. The coldest temperature ever measured on Earth's surface was −89.2°C at a research station in Antarctica in 1983, and one of the hottest, 56.7°C, was recorded in Death Valley in California in 1913.
People like to say that CLIMATE is what you expect and weather is what you get: climate is the long-term pattern of a place, weather is the day. RAIN, SNOW, WIND and every CLOUD begin with water that has risen from the land and sea, as our water cycle page explains. A RAINBOW, FOG, MIST, FROST, SLEET, DRIZZLE, a BLIZZARD, a BREEZE, HUMIDITY, SUNSHINE and a SUNNY day complete the FORECAST.