Weather Glossary - - Jackson, MS

Weather Glossary

Weather Glossary

Air Pressure - The force exerted on a surface by the weight of the air above it.  Meteorologists measure air pressure using a barometer. 


Atmosphere - The air surrounding and bound to the Earth.  The atmosphere is subdivided into four sections; they are:

  • Troposphere - From the ground to 7 miles in the air (Air planes can fly as high  6 or 7 miles in the air.)  This is also the section where our weather takes     place.
  • Stratosphere - From 7 miles to 25 miles in the air.
  • Mesosphere - From 25 miles to 50 miles in the air.
  • Thermosphere - More than 50 miles in the air.

Barometer - An instrument used to measure air pressure.


Climate - The average or typical weather conditions in an area observed over a long period of time.


Cloud – A visible cluster of tiny water droplets or ice crystals in the air.


Cold Front – The boundary that is the leading part of a cooler airmass.


Condensation – The process by which tiny water droplets, called water vapor (a gas), becomes a liquid.


Drizzle – Rain drops that have a diameter of 1/16th of an inch or less. 


Evaporation – The process by which a liquid (often water) turns into water vapor.


Fog – Droplets of water vapor suspended in the air at the ground. 


Front – The boundary between two different air masses.  Types of fronts include; cold, warm, stationary and occluded.  


Funnel Cloud – A cloud that extends from a thunderstorm cloud, called a Cumulonimbus cloud, that is associated with a rotating column of air that is NOT in contact with the ground. 


Hail – Occurs in thunderstorms.  Precipitation that falls as balls or clumps of ice.


High Pressure – In the Northern Hemisphere, an area of high atmospheric pressure with a clockwise movement of air.  The weather associated with a high pressure system is often quiet with only a few clouds.


Hurricane – A tropical low pressure system that forms over water.  Hurricanes have winds of 74 mph or greater and are measured using the Saffir-Simpson Scale.  Hurricanes can span several hundred miles in diameter, thus can affect a very large area.  Our hurricane season starts on June 1 and continues until November 30.


Low Pressure – In the Northern Hemisphere, an area of low atmospheric pressure with a counter-clockwise

movement of air.  The weather associated with a low pressure system is often cloudy and wet. 


Lightning – Generally, any and all of the various forms of visible electrical discharge produced by thunderstorms.


Meteorologist – A person who studies the weather.  There are many different paths within the field of meteorology.  For example, one could be a research meteorologist, radar meteorologist, climatologist or an operational meteorologist. 


Occluded Front – A boundary that separates a cold airmass from a cool airmass.


Precipitation – Moisture that falls from the air to the ground.  It includes rain, sleet, snow, hail, and drizzle.  Fog is NOT precipitation. 


Rain – Water droplets that fall from the air.


Severe Thunderstorm – A type of thunderstorm that has at least one of the following; 58 mph winds or greater, hail ¾” in diameter (the size of a nickel), and/or a tornado.


Severe Thunderstorm/Tornado WARNINGS – Issued by the National Weather Service for a specific weather hazard that is happening right now or is about to happen.  These warnings are issued for very specific areas, generally issued by county.  This is the time you need to act and take safety precautions from the weather.  Warnings usually last from 30 minutes to an hour.


Severe Thunderstorm/Tornado WATCHES – Issued by the Storm Prediction Center for a specific weather hazard that may happen.  Watches cover large areas.  When a watch is issued, you need to think about what you will do if the weather should turn bad.  Watches usually last for 3 to 6 hours.


Sleet – Frozen water droplets that have been frozen, thawed, and frozen again before they hit the ground.

Snow - Water droplets that fall through an atmosphere that is 32° F or below.


Stationary Front – A boundary between two airmasses that is not moving.


Temperature – The degree of hotness or coldness measured against some definite scale (For example, Fahrenheit, Celcius, or Kelvins) by a thermometer.


Thunderstorm – A cloud that produces rain, thunder and lightning.  Some thunderstorms have hail, wind and even tornadoes!


Tornado – A violent rotating column of air extending from a thunderstorm cloud to the ground.  Tornadoes can have winds over 300 mph and are measured using the Fujita Scale.  Tornadoes can vary in diameter from a couple hundred feet to a couple of miles.


Warm Front – A boundary that is the leading edge of a warmer airmass.


Weather – The changing of the atmosphere.


Wind – The movement of air.


Wind Chill – How cold it feels to your body when you combine the air temperature and the wind speed. 


Fujita Scale :  A scale of wind damage intensity in which wind speeds are inferred from an analysis of wind damage.

F0 - < 73 Light damage.  Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.


F1 - 73-112 Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads.


F2 - 113-157 Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.


F3 - 158-206 Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.


F4 - 207-260 Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.


F5 - 261-318 Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yards); trees debarked; incredible phenomena will occur.


Saffir-Simpson Scale :  A 1-5 rating based on the hurricane's present intensity.

Category One Hurricane :

Winds 74-95 mph.  Storm surge generally 4-5 ft above normal. No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Some damage to poorly constructed signs.

Category Two Hurricane :

Winds 96-110 mph.  Storm surge generally 6-8 feet above normal. Some roofing material, door, and window damage of buildings. Considerable damage to shrubbery and trees with some trees blown down. Considerable damage to mobile homes, poorly constructed signs, and piers.

Category Three Hurricane :

Winds 111-130 mph.  Storm surge generally 9-12 ft above normal. Some structural damage to small residences and utility buildings with a minor amount of storm shutter failures. Damage to shrubbery and trees with foliage blown off trees and large trees blown down. Mobile homes and poorly constructed signs are destroyed.

Category Four Hurricane :

Winds 131-155 mph.  Storm surge generally 13-18 ft above normal. More extensive storm shutter failures with some complete roof structure failures on small residences. Shrubs, trees, and all signs are blown down. Complete destruction of mobile homes. Extensive damage to doors and windows.  Major damage to lower floors of structures near the shore. Terrain lower than 10 ft above sea level may be flooded requiring massive evacuation of residential areas as far inland as 6 miles.

Category Five Hurricane :

Winds greater than 155 mph.  Storm surge generally greater than 18 ft above normal. Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. All shrubs, trees, and signs blown down. Complete destruction of mobile homes. Severe and extensive window and door damage.  Major damage to lower floors of all structures located less than 15 ft above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5-10 miles (8-16 km) of the shoreline may be required.


Tornado Safety Rules :  DUCK


Underneath Something

Center of Home/Building

Keep Away from Windows

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