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Weather Glossary

  • Anemometer - An instrument used to measure the speed of the wind.
  • Atmospheric pressure - The pressure exerted by the atmosphere at a given point. This is also called barometric pressure. Atmospheric pressure is measured with a barometer in units of millibars or inches of mercury.
  • Barometer - An instrument used to measure the pressure of the atmosphere.
  • Blizzard - A severe winter storm, defined as winds over 35 mph and visibility of ¼ mile or less due to falling or blowing snow, occurring for at least three hours.
  • Climate - The typical weather conditions of any place or region including not only the averages but also the variability and extremes of temperature, precipitation, wind, humidity, and sunshine. Several decades of information are used to derive a description of the climate.
  • Deforestation - The widespread removal of trees by natural or human forces.
  • Drought - A prolonged dry period that reduces water supplies for plants, streams, or human use, such as water wells. The 'Palmer Drought Severity Index' is a common measure of drought in the United States.
  • Flash flood - A flood that develops rapidly, often within a few minutes or hours, and gives little time for warning or escape from the floodwaters.
  • Flood - An overflow of a stream or river out of its banks due to heavy rains or snowmelt.
  • Flood plain - The relatively flat area adjacent to a stream that is covered by water when the stream overflows its banks during a flood. The 100-year flood plain is defined as those areas near a stream that have a 1% chance of being flooded in any given year.
  • Flood stage - A locally defined height of water in a stream, above which the water causes damage or interferes with local travel or other activities. It is specified as the height in feet above some baseline elevation.
  • Freezing rain - Precipitation that falls to the ground as liquid water, but freezes as ice upon contact with roads or sidewalks, or objects such as trees or wires. It occurs when warm air with temperatures above freezing overlies cold air at the surface with temperatures below freezing. Freezing rain is also called glaze or an ice storm.
  • Gale - A strong wind of 32 to 63 mph on the international Beaufort Wind Scale. The National Weather Service issues a gale warning on Lake Erie if sustained winds of 40-58 mph are expected.
  • Gust - A sudden, brief increase in wind speed.
  • Hail - A type of precipitation formed in thunderstorms. Repeated updrafts and downdrafts cause layers of ice to develop on ice pellets until the ball of ice is large enough to fall through the updrafts to the ground. Hail as large as baseballs has been recorded in Ohio.
  • High pressure - An area of a relative atmospheric pressure maximum that has diverging winds and rotation clockwise in the northern hemisphere. It is also called an anticyclone.
  • Humidity - A measure of the amount of moisture in the air as water vapor.
  • Hurricane - The name used in the Atlantic Ocean and eastern Pacific Ocean for a tropical cyclone with sustained winds of 74 mph or greater. These are known as typhoons in the western Pacific Ocean and cyclones in the Indian Ocean. They are an area of extreme low pressure with winds that rotate counter-clockwise in the northern hemisphere. Although they form over tropical oceans, they can bring heavy rains hundreds of miles inland.
  • Ice age - A period in the Earth's history during which a colder and wetter climate led to growth of glaciers and extensive ice sheets over northern North America and Europe. There have been several ice ages. The most recent occurred about 18,000 years ago when an ice sheet extended from northern Canada across much of Ohio.
  • Landform - A natural feature of a land surface.
  • Lightning - A sudden, powerful discharge of electricity produced in response to a build-up of electrical potential between a cloud and the ground, between clouds, or within a cloud. Lightning occurs during thunderstorms and poses a significant risk of injury to persons outdoors. The rapid expansion of air due to the extreme heat of lightning causes a sound wave called thunder.
  • Low pressure - An area of a relative atmospheric pressure minimum that has converging winds and rotatation counter-clockwise in the northern hemisphere. It is also called a cyclone.
  • Mesoscale convective system (MCS) - A large organized convective weather system comprised of a number of individual thunderstorms. It persists for several hours and may be rounded or linear in shape. Severe weather, including tornadoes, floods and high winds, may occur with an MCS.
  • Microburst - A severe, localized wind from a thunderstorm. It covers an area of 3 miles or less and usually lasts less than 5 minutes. Damage may resemble that from a tornado. Because the microburst does not rotate like a tornado, it is sometimes called a straight-line wind. A general term for this feature is a downburst.
  • Mystery wave - A wave of water that is larger than prevailing waves and that occurs without an obvious cause. They may be caused by a localized, but distant, strong wind, a shift in underwater surfaces due to an earthquake, or a large object striking the water surface.
  • National Weather Service - A branch of the United States government that collects and analyzes weather information and issues weather forecasts and warnings.
  • Outflow boundary - The outward flow of air at the surface from a thunderstorm. It is caused by downdrafts in the thunderstorm and may instigate additional thunderstorms.
  • Precipitation - The fall of water from the atmosphere in the form of rain, drizzle, sleet, snow, or hail.
  • Snow - Frozen precipitation in the form of branched, six-sided ice crystals. Snow usually appears clustered into snowflakes.
  • Snowbelt - A region downwind of a large lake that is prone to frequent, heavy winter snowfalls. Cold air passing over the warmer lake waters causes excessive evaporation and instability, leading to 'lake-effect' clouds and snowfall. In Ohio, the region east of Cleveland in Lake, Geauga, and Ashtabula counties is the snowbelt. Average annual snowfall is 80 to 100 inches in the snowbelt.
  • Stationary front - A boundary between two different air masses that moves little over the course of several hours or a day.
  • Storm - The occurrence of destructive or unpleasant weather, often with a strong wind and heavy precipitation.
  • Storm system - A low pressure area and its associated contrasting air masses, fronts, clouds, and precipitation, that cover an area of several states and bring various changes of weather. They last several days and generally travel west-to-east across the United States.
  • Straight-line winds - Any surface wind that is not associated with rotation or a tornado. Usually associated with damaging winds from a thunderstorm, such as a microburst.
  • Temperature - A measure of the degree of heat in a substance.
  • Thermometer - An instrument used to measure the temperature of a substance.
  • Thunderstorm - A cumulonimbus cloud with lightning and thunder. A thunderstorm may also contain hail, high winds, rain, strong vertical winds, or tornadoes.
  • Tornado - A violently rotating column of air in contact with the ground. It typically forms from a thunderstorm. Tornadoes are ranked F0 to F5 on the Fujita Tornado Intensity Scale based on their intensity and damage. A typical tornado lasts a few minutes, is a few hundred yards wide, and has winds of about 100 mph.
  • Tornado family - A series of tornadoes that develops over an hour or more from the same thunderstorm or thunderstorm complex. A tornado family may cause a sporadic damage path over 100 miles long.
  • Violent tornado - A tornado that is rated F-4 or F-5 on the Fujita Tornado Intensity Scale. Maximum winds in a violent tornado exceed 200 mph. A violent tornado can destroy a well-built house.
  • Weather - The condition of the atmosphere at a specific time and the variations of the atmosphere over several days. Elements such as temperature, wind speed, wind direction, cloud cover, humidity, and precipitation are used to describe the weather.
  • Wind chill - A temperature value that takes into account the effects of air temperature and wind speed on exposed human skin. It is not the actual temperature, but describes the average loss of heat from the body and how the combination of temperature and wind feels on skin.