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Weather?

Why the sky does what it does, and what the warnings actually mean. 30 questions and counting.

How do hurricanes form?Warm ocean water is the fuel. Hurricanes form over seas above about 80F, where rising warm moist air creates a spinning…
How do you tell how far away lightning is?Count the seconds between the flash and the thunder, then divide by five for miles (or three for kilometers). Sound travels…
What is the difference between a hurricane, a typhoon, and a cyclone?Nothing meteorological. They are the same storm with three regional names: hurricane in the Atlantic and eastern Pacific…
Is a car safe during a lightning storm?Yes, but not for the reason people think. It is not the rubber tires; it is the metal shell, which channels lightning around…
What causes a rainbow?Sunlight bending through raindrops. Each drop splits white light into its colors and reflects them back, so you need sun…
What does a 30 percent chance of rain actually mean?Not what most people think. It roughly combines the forecaster's confidence that it will rain with how much of the area will…
What is humidity, and why does it make heat feel worse?Humidity is water vapor in the air. It makes heat brutal because sweat cools you by evaporating, and humid air is already…
What is the difference between a tornado watch and a warning?A watch means conditions are right for a tornado, be ready. A warning means one has been spotted or shows on radar, take…
Why does it rain?Water evaporates, rises, and cools into clouds; when droplets grow heavy enough, gravity wins and they fall as rain. It is…
Why does it snow sometimes instead of rain?It comes down to the temperature the precipitation falls through. Snow forms in cold clouds and stays snow if the air below…
What causes wind?Wind is air moving from high pressure to low pressure, and that pressure difference comes from uneven heating by the sun…
Why is the sky blue but sunsets red?Both from the same cause: air scatters blue light most. Overhead, that scattered blue fills the sky. At sunset, light…
What do hurricane categories actually mean?Categories 1 through 5 on the Saffir-Simpson scale rate sustained wind speed only. They say nothing about storm surge…
What causes hail?Strong updrafts in a thunderstorm carry raindrops high enough to freeze, then hold them aloft while more ice layers on. The…
What causes thunder?Lightning heats the air along its channel to roughly five times the surface temperature of the sun in a fraction of a…
What is the difference between a weather watch and a warning?A watch means conditions are favorable and you should prepare. A warning means it is happening or imminent and you should…
How accurate are weather forecasts?Better than most people think. A five-day forecast today is about as accurate as a one-day forecast was in 1980. Accuracy is…
What causes fog?Fog is a cloud sitting on the ground. It forms when air cools to its dew point and water vapor condenses onto tiny…
What does the heat index actually measure?How hot it feels once humidity blocks your sweat from evaporating. High humidity means sweat sits on your skin instead of…
What is the polar vortex?A permanent ring of cold, fast winds high over the poles. It is always there. The extreme cold snaps happen when it weakens…
What is wind chill, and is it a real temperature?It is real as a measure of how fast you lose heat, not as an air temperature. Wind strips away the warm layer your body…
Why do deserts get so cold at night?Because dry air holds almost no heat and there is no water vapor to trap outgoing infrared radiation. Sand also sheds heat…
Why is it colder at the top of a mountain if it is closer to the sun?Because proximity to the sun is irrelevant at that scale, a mountain gets you a rounding error closer to a star 93 million…
What is lake-effect snow?Snow produced when cold air crosses a relatively warm lake, picks up moisture and heat, and dumps it as intense narrow bands…
Why is there sometimes lightning without thunder?There is not. Every lightning stroke makes thunder, but the sound rarely carries beyond about ten miles, so distant…
What is a bomb cyclone?A storm whose central pressure drops at least 24 millibars in 24 hours, a process called bombogenesis. The name is technical…
What is El Nino?A periodic warming of the central and eastern tropical Pacific that shifts weather patterns worldwide. It typically brings…
What actually counts as a drought?Less water than normal for that place over a sustained period, which means drought is defined relative to local expectations…
What is a microburst?A sudden downdraft from a thunderstorm that hits the ground and spreads out violently, producing winds that can exceed 100…
What is a derecho?A long-lived line of intense straight-line windstorms that travels hundreds of miles, causing damage comparable to a tornado…