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Weather terms
- Observation
- A measurement taken by a weather station at a specific time.
- Forecast estimate
- A value from a forecast model for the current time, not a measurement.
- Chance of precipitation
- The probability that measurable precipitation falls during a period. 40% means rain in 4 out of 10 similar situations, not rain for 40% of the time.
- Wind chill
- How cold it feels on exposed skin when wind combines with low temperatures.
- Heat index / Humidex
- How hot it feels when humidity combines with high temperatures (heat index in the U.S., humidex in Canada).
- Gust
- A brief increase in wind speed, usually lasting seconds.
- Sea-level pressure
- Air pressure adjusted to sea level so stations at different heights can be compared.
- UV index (clear-sky)
- Expected UV strength if there were no clouds; actual UV is often lower.
- Polar day / night
- Days when the sun does not set, or does not rise, at high latitudes.
