Severe Weather Glossary - - Columbia, South Carolina

Severe Weather Glossary

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Here are some of the terms you'll likely hear during the threat of tropical weather.

Barometric Pressure: The weight of the column of air that extends from the ground (or water's surface) to the top of the atmosphere. It is also called air pressure. Barometric pressure is very low in a hurricane.

Convective Organization: The patterns of wind flow that work together to create conditions in which severe weather can form.

Cyclone: A closed, rotating wind. Cyclones rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Doppler Radar: A radar that compares in frequency, up or down from the original signal, echoes returned from weather systems to create highly-accurate measurements of the weather system's velocity.

Extratropical Cyclone: A storm that forms outside the tropics, sometimes as a tropical storm or hurricane changes.

Eye: The low pressure center of a hurricane. Winds are normally calm and sometimes the sky clears.

Eye Wall: The ring of thunderstorms that surrounds a storm's eye. The heaviest rain, strongest winds and worst turbulence are normally in the eye wall.

Flash Flood Watch: Flash flooding conditions could pose a threat. You should decide which valuables you may need to move and how your family can escape the area

Flash Flood Warning: Flash flooding conditions are imminent. Immediate action should be taken to protect your family and property.

Gale Warning: Sustained surface winds between 39 mph and 54 mph are reported or predicted.

High Wind Warning: Surface winds of 40 mph or greater, lasting for an hour or longer, or winds gusting up to 58 mph or greater regardless of duration are expected or are already reported over land.

Hurricane: A tropical cyclone with winds of 74 mph or more.

Hurricane Watch: Hurricane conditions are possible within 48 hours.

Hurricane Warning: Hurricane conditions are expected within 36 hours.

Knot: Measure of speed. It is one nautical mile per hour.

Landfall: The intersection of the surface center of a tropical cyclone with a coastline.

Low-Pressure Trough: An extended area of relatively-lower atmospheric pressure that can be the extension of a cyclone and is generally associated with severe weather.

Major Hurricane: A hurricane that is classified as Category Three or higher.

Millibar: A measurement of air pressure.

Remnant Low: Used for systems no longer having the sufficient convective organization required of a tropical cyclone.

Small Craft Advisory: A warning of sustained surface winds between roughly 25 mph and 38 mph, predicted or occurring not directly associated with tropical cyclones.

Squall Line: A line of severe thunderstorms that can form along or ahead of a cold front. The line contains heavy precipitation, and often hail, frequent lightning, strong straight-line winds and possibly tornadoes and waterspouts.

Storm Surge: The dome of water that builds as a hurricane moves over water.

Storm Tide: A combination of storm surge and the normal tide.

Sustained Winds: The wind speed defined by the average wind measurement recorded over a one-minute period.

Tornado Watch: Conditions are favorable for a tornado to develop, though a tornado has not currently been spotted. Be prepared to move to a safer location in a hurry if necessary.

Tornado Warning: A tornado has been reported or detected by Doppler radar. Take action immediately to protect yourself and your family. Do not delay!

Tropical Cyclone: A low-pressure weather system in which the center of the storm is warmer than the surrounding atmosphere.

Tropical Depression: A tropical cyclone with maximum sustained winds of less than 39 mph.

Tropical Disturbance: The earliest stages of a tropical cyclone, with winds less than 30 mph.

Tropical Storm Watch: Tropical storm conditions are possible within 48 hours.

Tropical Storm Warning: Tropical storm conditions are expected within 36 hours.

Tropical Wave: A bend in the normally straight flow of surface air in the tropics which forms a low pressure trough and showers and thunderstorms. This can develop into a tropical cyclone.

Typhoon: A hurricane in the north Pacific-west of the International Date Line.

Upper Level Low: An area of cold air aloft that is rotating counter-clockwise.

Waterspout: A waterspout is a tornado that passes over water. It is a funnel-shaped formation of wind, water and ocean spray.

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