Science / Weather Glossary

Hook Echo: A radar reflectivity pattern observed in a thunderstorm, appearing like a fish hook and indicating favorable conditions for tornadic development. However, hook echoes and tornadoes do not al . . . View Full Definition

Horizon: One of several lines or planes used as reference for observation and measurement relative to a given location on the surface of the earth. The geographic horizon, also called the apparent ho . . . View Full Definition

Horse Latitudes: Located between 30° North and 30° South in the vicinity of the equator, this area typically has calm or light and variable winds.

Hudson Bay Low: An area of low pressure over or near the Hudson Bay area of Canada that often introduces cold air to the north central and northeast United States.

Humboldt Current: Also known as the Peru Current, this ocean current flows northward along the western side of South America, offshore Chile and Peru. There is considerable upwelling of the colder subsurface . . . View Full Definition

Humidity: The amount of water vapor in the air. It is often confused with relative humidity or dew point.

Hurricane: The name for a tropical cyclone with sustained winds of 74 miles per hour (65 knots) or greater in the North Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in the eastern North Pacific O . . . View Full Definition

Hurricane Warning: A formal advisory issued by forecasters at the National Hurricane Center when they have determined that hurricane conditions are expected in a coastal area or group of islands within a 24 ho . . . View Full Definition

Hurricane Watch: A formal advisory issued by forecasters at the National Hurricane Center when they have determined that hurricane conditions are a potential threat to a coastal area or group of islands with . . . View Full Definition

Hydrologic Cycle: Often called the water cycle, it is the vertical and horizontal transport of water in all its states between the earth, the atmosphere, and the seas.

Hydrology: The study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water in streams, lakes, and on or below t . . . View Full Definition

Hydrometeor: Any any form of atmospheric water vapor, including those blown by the wind off the earth's surface. Liquid or solid water formation that is suspended in the air includes clouds, fog, ice fog . . . View Full Definition

Hydrosphere: Considered as the water portion of the earth's surface. Part of the geosphere.

Hygrograph: An instrument that records the hygrometer's measure of water vapor.

Hygrometer: An instrument that measures the water vapor content of the atmosphere.

Hypothermia: This situation occurs when the core temperature of one's body falls below normal. It is the failure of the body to maintain adequate production of heat under conditions of extreme cold.

Ice: The solid form of water. It can be found in the atmosphere in the form of ice crystals, snow, ice pellets, and hail for example.

Ice Crystals: Precipitation in the form of slowly falling, singular or unbranched ice needles, columns, or plates. They make up cirriform clouds, frost, and ice fog. Also, they produce optical phenomena s . . . View Full Definition

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