Weather types Types of Weather Weather type 1 - Clouds There are four basic types of clouds. High clouds, middle clouds, low clouds, and clouds with vertical developement. There are also clouds that don't fall into any of these groups. Low clouds are from the surface to about 6,500 feet and are usually composed of water droplets unless temperatures are several degrees below freezing. Clouds on the ground are called fog. Middle clouds range from about 6,500 feet to about 20,0000 feet. They are also mostly composted of water droplets unless temperatures are cold. High clouds are above 20,000 feet and are composed of ice crystals. Click the link to get the whole story on clouds . Weather type 2 - Dust Storm Dust storms are created by winds moving across an arid region. Many times a strong dry cold front is the mechanism that creates the dust or sand storm. As strong winds move across an arid landscape, sand or dirt is picked up from the ground. Sometimes the lighter dust particles can be lifted up to 20,000 feet high into the atmosphere.

A classic example of this is a sand and dust storm that develops over the Sahara desert. Easterly winds may carry the dust particles across the Atlantic ocean to the Caribbean Islands or Florida. Severe sand and dust storms can obscure visibility to zero and last for days. Picture courtesy of NOAA, George E. Marsh. Weather type 3 - Fog Fog is a stratus cloud on the ground. There are several types of fog. Advection fog is produced by a hortizontal motion of warm moist air over colder ground. An example of this would be a warm front moving across land with a recent snow or cold weather. Radiation fog is produced as heat from the earth surface is radiated back to space at night. A moist layer and nearly calm winds need to be present. Wind can mix in dryer air aloft, keeping the air below the saturation point. Steam fog forms when cold air moves over relatively warm water. This can be observed as wisps of "steam" rising from lakes, rivers or oceans when a cold air mass moves in. Upslope fog occurs as air is pushed up a mountainside and becomes saturated so that condensation occurs.

Fog photographs courtesy of Rich Johnson and NOAA Weather type 4 - Freezing Rain / Ice Freezing rain - known as "ice" occurs when a thin layer of freezing or below freezing air exists near the earth's surface. Typically this occurs when snow falls into warmer air changing the precipitation into rain. If a very thin layer of freezing air is present near the ground the rain will freeze on objects such as power lines, trees, and cars. Ice accumulations begin to cause serious problems when the ice is 1/2" or greater on objects. Freezing rain pictures courtesy of Nick Stefano. Weather type 5 - Hail The exact processes that creates hail are still being studied. Traditionally, textbooks showed hailstones being formed as a water droplet was carried aloft with an updaft into subfreezing air and freezing. As the ice moved into a downdraft, more water coated the hailstone. The cycle continued with the hailstone continuing to grow with each ride up and down the updraft and downdraft. More recent studies suggest that super cooled water droplets are carried aloft by strong updrafts in thunderstorms.

A small ice particle forms and grows as "waves" of supercooled water droplets continue to bump into the ice particle. A new coat of ice grows with each cycle. The hailstone is kept aloft by the strong updraft. The stronger the updraft the greater the force to keep the heavier hailstones aloft. The hailstone eventually falls to the grown when the the weight is too great for it to remain aloft or when it gets pushed out of the updraft. Sometimes hailstones bump into each other while being bombarded with supercooler water droplets and stick together giving the hailstone a spiked appearance. The largest known hailstone fell on Vivian, South Dakota on July 23, 2010. The hail stone weighed 1.9 pounds and was eight inches in diameter. The previous record was from a storm on June 23, 2003 in Aurora, Nebraska and had a diameter of seven inches and weighed almost one pound. Another heavy hailstone fell in Coffeeville, Kansas on September 3, 1970. It weighed 1.7 pounds. Hail is considered severe when the diameter reaches one inch or quarter size.

Hail photographs courtesy of NOAA and Jim Reed - jimreedphoto.com Weather type 6 - Hurricane Check out our complete library on hurricanes on our hurricane school page. We also have hurricane tracking charts so that you can follow the path of hurricanes. Check out just about anything you want to know about hurricanes on the hurricane library tab at the top menu. Hurricane pictures courtesy of NOAA. Weather type 7 - Lightning Lightning is simply a discharge of electricity in the atmosphere. For a complete look at this interesting phenomenon, check the facts about lightning page. Lightning photographs courtesy of Jim Reed - jimreedphoto.com Weather type 8 - Rain Rain is precipitation in liquid form. Liquid precipitation can occur as mist, drizzle, or rain. Droplet size differentiates the type that it is classified. Mist is generally 50-500 microns in size. Drizzle is .5 to 2 millimeters in size and rain is 2 millimeters to 1 centimenter in size. Rain is formed when condensation of water vapor occurs condenses into water droplets. Precipitation in the form of rain can be created in a number of different ways. First, two types of processes cause minute droplets to form rain drops.

Collision coalescence is a process where tiny droplets gradually grow in size by bumping into each other and growing. This is mostly a warm cloud process where temperatures are above freezing. The second process is a cold cloud process where super cooled water droplets freeze on ice nuclei. These ice nuclei grow into ice crystals. The snowflakes fall and turn into rain drops as the temperatures rise above freezing closer to the ground. This is the primary process that produces rainfall. Lifting to produce rainfall occurs in a number of differnt ways. 1. A low pressure system and associated fronts 2. Mountains or higher terrain 3. Atmospheric convection Weather type 9 - Sleet Sleet is transparent frozen raindrops. Sleet or ice pellets are created when snow falls into air above freezing and melts into rain drops. If another below freezing layer below the warm air is of sufficient depth, the rain drops freeze into balls of ice or ice pellets. Any significant amount of sleet is farily rare. This is due to the fact that there needs to be just the right conditons to get a perfect layer of warm air in between the layers of cold air. There have been cases of storms producing several inches of sleet.

A mix of snow and sleet and sleet and rain is more common. Sleet pictures courtesy of NOAA. Weather type 10 - Snow Snow is the accumulation of crystal snowflakes. Snowflakes are made as water ice crystalizes. The crystals may form in many different shapes dictated by the water content and temperature in the cloud as the snowflakes are forming. Snowflakes can take the shape of columns, dendrites, plates, needles and other six sided shapes. It is possible for it to snow several degrees above freezing if the air aloft is very cold and the above freezing layer is shallow near the ground. The greatest 24 hour snowfall in North America was 76" Silver Lake, Colo. April 14–15, 1921. The greatest amount of snow for one storm in North America was 189" at Mt. Shasta Ski Bowl, California, Feb. 13–19, 1959. The one season snowfall record for North America was 1,140" at Mount Baker, Wash. 1998–1999. Snow pictures courtesy of winter weather expert Paul Kocin.

Weather type 11 - Sun Sunny weather or clear skies is defined as less than 1/8 sky cloud cover. Mostly sunny skies is characterized by 1/8 - 2/8 sky cloud cover. Sunny skies many times are observed when a high pressure area is dominating the weather pattern. High pressure signifies a region of sinking air which tends to dry out the atmosphere resulting in less mositure to form clouds. Deserts are locations with sunny or mostly sunny skies due to high pressure systems influencing the weather pattern much of the year. Weather type 12 - Thunderstorm Thunderstorms are cumulonimbus clouds that produce thunder and lightning. Discover more about thunderstorms here. Thunderstorm photographs courtesy of NOAA / NSSL and Rich Johnson. Weather type 13 - Tornado A tornado is a violently rotating column of air usually produced by severe thunderstorms. For much more about tornadoes, check out our tornadoes page. Tornado photographs courtesy of Jim Reed. jimreedphoto.com Weather type 14 - Wind Wind is air in motion in the atmosphere. Windy weather is caused by an imbalance of heating in the atmosphere. It can be caused from an imbalance from solar heating or a difference over a boundary such as a front.

The uneven heating generates an unbalanced pressure field. Air from a high pressure area flows toward a region of low pressure to balance the pressure field. A wind vane points to the direction from where the wind is blowing from and an anemometer measures how fast the wind is blowing. The strongest surface wind gust was 253 mph on Australia's Barrow Island during Cyclone Olivia in 1996. The previous wind record was 231 mph set on top of Mount Washington, New Hampshire on April 12, 1934. Photographs courtesy of Rich Johnson and the Sydney Morning Herald. Talk about weather on the weather message boards . Weather News - AccuWeather.com Weather News PHOTOS: First snow in decades coats Murcia, Spain January 19, 2017, 12:12:54 PM EST Low elevations of southeastern Spain received a rare coating of snow this week with snowflakes set to next make an appearance in Madrid.

Major storm to raise flooding risk in northeastern US amidst warmth next week January 19, 2017, 10:42:17 AM EST A major storm with drenching rain, gusty winds and the risk of flooding will accompany temperatures more fitting for March and April in the northeastern United States early next week. The world's largest earthquake detection network is pocket sized January 19, 2017, 9:50:41 AM EST Citizens around the world now have the opportunity to be part of one of the newest scientific developments in earthquake research using only their smart phones. Germany: Relief from harsh cold to be limited to northern areas into Saturday January 19, 2017, 9:15:35 AM EST Some relief from the recent harsh cold will come to Germany later this week but only across northern areas. Brothers create massive snow sculptures to raise money for clean water around the world January 19, 2017, 8:35:54 AM EST The Bartz brothers build elaborate snow sculptures not just for themselves but also to help others through charity.

Severe thunderstorms to erupt over southeastern US this weekend January 19, 2017, 7:11:00 AM EST Damaging winds, torrential downpours, hail and tornadoes are among the weather phenomena expected to threaten the Southeast this weekend. India: Children among the two dozen dead in bus crash amid dense fog January 19, 2017, 6:50:54 AM EST At least 24 people, with the vast majority children, died on Thursday when a truck crashed into a school bus amid dense fog southeast of New Delhi, India. January 19, 2017, 6:07:25 AM EST Heavy rain moves south to Southern California as the first round of flooding tapers off throughout Thursday. January 18, 2017, 1:13:52 PM EST 2016 was the third consecutive year with global temperatures soaring to record highs.

Spain: Late-week snow to bury mountains, bring rare coating to low elevations January 18, 2017, 11:59:54 AM EST A winter storm will continue to allow snow to fall across southeastern Spain late this week with even some communities outside of the mountains receiving a rare coating. Weather - Bulbapedia, the community-driven Pokémon encyclopedia Please feel free to edit this article to add missing information and complete it. Reason: Generation VI details; Gates to Infinity descriptions. The weather (Japanese: 天気 weather) is a set of mechanics in the Pokémon games that change the battle environment, activating Abilities , modifying certain moves , and potentially damaging the Pokémon in battle or affecting their stats . They have been included in every main series game since Generation II . In battle, weather is either determined by the location of a battle, due to overworld weather, or by a Pokémon creating a new type of weather with a move or Ability. Only one type of weather may be present at a time, and only the most recent type of weather will take effect. In Generation II, only moves that cause weather were introduced and weather was only present in battles, not in the overworld.

Generation III introduced overworld weather and weather-related Abilities , as well as a new weather-causing move. The biggest modification to weather in Generation IV was the introduction of four rocks that, when held, would increase the duration of weather caused by a weather move. Generation V mostly introduced greater overworld weather variability, especially in seasons affecting the weather in certain locations. Contents Types of weather and effects Overview Clear skies: Actually the absence of weather. This is the weather found in most locations. Harsh sunlight : Strong sunlight shines on the battlefield. This has only occurred in the overworld in the Hoenn region, in Pokémon Ruby and Emerald , due to Groudon 's emergence. Extremely harsh sunlight : Sunlight shines more heavily on the battlefield. This has only occurred in the overworld in the Hoenn region, in Pokémon Omega Ruby , due to Groudon 's emergence. Rain : Rain falls on the battlefield. Different variations of this weather may appear on the overworld. This is the most common weather pattern that may be found on routes and occasionally in cities. Heavy rain : Rain falls more chaotically around the battlefield.

This has only occurred in the overworld in the Hoenn region, in Pokémon Alpha Sapphire , due to Kyogre 's emergence. Sandstorm : Stinging sand whips across the battlefield. In Generations III through V , every new region had a specific area where a sandstorm was always occurring. Hail : Pelting hail falls on the battlefield. Different variations of this weather may appear on the overworld, and there may even be benign falling snow that does not cause hail in a battle. Diamond dust : A special, purely aesthetic version of snow. It was an easter egg first revealed in Pokémon Diamond and Pearl , and is known to appear in every core game since. Shadowy aura : Bursts of light rain down from a shadowy aura in the sky. This type of weather is only present in Pokémon XD: Gale of Darkness and has no overworld manifestation anywhere. Fog : A thick fog clouds the battlefield. This only had an in-battle effect during Generation IV, but it has been present in the overworld in other Generations in a purely aesthetic form. Mysterious air current : A strong air current blows across the battlefield. This weather can only be present in battle, as a result of Mega Rayquaza 's Ability.

There is also a glitch that occurs in Pokémon Platinum , HeartGold and SoulSilver , called acid rain , that results in the simultaneous occurrence of all then-existing weather conditions at once, damaging all Pokémon on the field. In Generation V , the weather was given an icon which appeared on the DS or 3DS's bottom screen in a battle whenever weather was occurring. Since fog and shadowy aura do not appear in-battle in Generation V, they have no icons. When there is no weather, no icon is shown. Game Delta Stream In addition, Defog may clear fog from an overworld area (in Generation IV only). It is the only move that has any effect on weather in the overworld. Weather normally lasts for 5 turns when it is called by a move. Prior to Generation VI , weather created by an Ability would continue until the battle ended or another type of weather took its place; since Generation VI, weather created by Abilities also lasts for only 5 turns, with the exception of weather created by Desolate Land , Primordial Sea , and Delta Stream . If a Pokémon holding one of four held items creates weather that would otherwise last 5 turns, it instead lasts 8 turns. The rock that affects each type of weather is shown below.

Icy Rock Effects Three of the types of weather can do damage to Pokémon in battle at the end of a turn. In a sandstorm , hail , or shadowy aura , any Pokémon that is not Rock -, Ground -, or Steel-type ; Ice-type ; or a Shadow Pokémon (respectively) will be damaged for 1/16 of its maximum HP. Certain Abilities prevent damage from weather effects, though, and a Pokémon holding Safety Goggles is also immune to damage from weather effects. Sandstorm and fog both affect the stats of Pokémon on the battlefield. Since Generation IV, in a sandstorm, the Special Defense of Rock-type Pokémon is increased by 50%. In fog, the accuracy of all Pokémon in battle is decreased. During harsh sunlight , all Pokémon are immune to freezing . Harsh sunlight and rain both affect the power of certain types of moves . Harsh sunlight strengthens the power of Fire-type moves by 50% and weakens the power of Water-type moves by 50%, while rain does the opposite, strengthening Water-type moves by 50% while weakening Fire-type moves by 50%. Certain specific moves are also affected in special ways by the weather.

The recovery moves Synthesis , Morning Sun , and Moonlight will recover different amounts* of HP depending on the weather: in clear skies, they recover 1/2 of the user's maximum HP; in harsh sunlight, they recover 2/3 HP; and in other types of weather, they recover 1/4 HP. The accuracy of Thunder , Hurricane , and Blizzard is affected by the weather. In hail, Blizzard ignores accuracy and evasion checks*, while Thunder* and Hurricane do the same in rain. During harsh sunlight, however, Thunder and Hurricane only have 50% accuracy. In Pokémon Diamond and Pearl , Blizzard and Thunder also had a 30% chance to hit through Protect or Detect when used in their favored weather. Solar Beam becomes a 1-turn move in harsh sunlight, skipping its charge turn, but in rain, sandstorm, or hail, Solar Beam's power is halved. Growth 's stat increases double in harsh sunlight (since Generation V). When used as a field move in Generation IV or later, Sweet Scent will fail to work if there is a type of weather in effect in the area. Activated Abilities The following Abilities are activated when a type of weather comes into effect.

Unless a type of weather is in effect, none of these Abilities has any effect. Dragon In the Pokémon Mystery Dungeon series Various weather effects appear in certain dungeons in the Pokémon Mystery Dungeon series . Weather effects can change from floor to floor, and can also be altered through the use of Wonder Orbs . In Gates to Infinity and Super Mystery Dungeon , Pokémon will regenerate HP only if the weather is Clear, or if it is holding a Weather Band . Clear: None R B T D S , Pokémon will resore health as turns go by GtI SMD Sunny: Fire-type moves increase power by 50%, while the power of Water-type moves is cut in half. Fog: The power of Electric-type moves is cut in half. Also turns Castform into a Water type. Snow: Ice-type Pokémon have an increased movement speed . Also turns Castform into an Ice type. Rain: Water-type moves increase power by 50%, while the power of Fire-type moves is cut in half. Also prevents explosions from traps and moves like Selfdestruct . Hail: Deals 5 R B /3 T D S /1 GtI points of damage to non-Ice types every 10 turns.

Sandstorm: Deals 5 R B /3 T D S /1 GtI points of damage to non-Rock, Ground, and Steel types every 10 turns. Cloudy: Reduces the damage of all non-Normal-type moves by 25%. Gates to Infinity descriptions Weather Glossary – Terms & Definitions Home Weather Weather Glossary – Terms & Definitions Weather Glossary – Terms & Definitions Below is a list of weather terms that are described in weather reports, forecasts and readings. This data is collected from: the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service; the Met Office in the United Kingdom; Canada’s Weather Office; and the Australian Government Bureau of Meteorology. Top Acid rain Cloud or rain droplets containing pollutants, such as oxides of sulfur and nitrogen, to make them acidic (eg. pH < 5.6). Afternoon Noon to sunset. Arctic air A mass of very cold, dry air that usually originates over the Arctic Ocean north of Canada and Alaska.

Arctic high Top Ball lightning A relatively rarely seen form of lightning, generally consisting of an orange or reddish ball of the order of a few cm to 30cm in diameter and of moderate luminosity, which may move up to 1 m/s horizontally with a lifetime of a second or two. Barber pole A thunderstorm updraft with a visual appearance including cloud striations that are curved in a manner similar to the stripes of a barber pole. The structure typically is most pronounced on the leading edge of the updraft, while drier air from the rear flank downdraft often erodes the clouds on the trailing side of the updraft. Barometer An instrument for measuring atmospheric pressure. Barometric pressure The actual pressure value indicated by a pressure sensor. Bitterly cold In winter, bitterly cold or very cold, refers to more than seven degrees Celsius below normal. Black ice Thin, new ice that forms on fresh water or dew covered surfaces; it is common on roadways during the fall and early winter and appears "black" because of its transparency.

Blizzard Includes winter storm conditions of sustained winds or frequent gusts of 35 mph or more that cause major blowing and drifting of snow, reducing visibility to less than one-quarter mile for 3 or more hours. Extremely cold temperatures often are associated with dangerous blizzard conditions. In Canada, a blizzard described as a severe storm that lasts three or more hours, and brings low temperatures, strong winds and poor visibility due to blowing snow. In Australia, it is described as a violent and very cold wind which is loaded with snow, some of which has been raised from snow covered ground. Blocking high A high pressure area (anticyclone), often aloft, that remains nearly stationary or moves slowly compared to west-to-east motion. It blocks the movement eastward movement of low pressure areas (cyclones) at its latitude. Blowing Dust Dust that is raised by the wind to moderate heights above the ground to a degree that horizontal visibility decreases to less than seven miles. Visibilities of 1/8 mile or less over a widespread area are criteria for a Blowing Dust Advisory. Blowing sand Sand particles picked up from the surface of the earth by the wind to moderate heights above the ground, reducing the reported horizontal visibility to less than seven statute miles.

Blowing snow Wind driven snow that reduces visibility to six miles or less causing significant drifting. Blowing snow may be snow that is falling and/or loose snow on the ground picked up by the wind. In Canada, it is described as snow that is lifted by the wind from the earth's surface to a height of two meters or more. Blowing spray Water droplets torn by the wind from a body of water, generally from the crests of waves, and carried up into the air in such quantities that they reduce the reported horizontal visibility to less than seven statute miles. Blustery Descriptive term for gusty winds that accompany cold weather. Breezy Wind in the range of 15 miles per hour to 25 mile per hour with mild or warm temperatures. Brisk Wind in the range of 15 to 25 miles per hour when the temperature is cold. Broken clouds The absence of apparent motion in the air. Celsius A temperature scale in which zero is the freezing point of water and one hundred is the boiling point. Chinook A Chinook is a warm, dry, gusty wind that occasionally occurs to the leeward side of a mountain range, particularly the Rocky Mountains.

Cirrus cloud High cloud, delicate, hair-like and feathery looking. Clear Sky condition of less than 1/10 cloud coverage. In the United Kingdom, clear is defined as “No cloud”, and in Australia, it is defined as “Virtually cloud-free”. Clear slot A local region of clearing skies or reduced cloud cover, indicating an intrusion of drier air; often seen as a bright area with higher cloud bases on the west or southwest side of a wall cloud. Climate The prevalent long term weather conditions in a particular area. Climatic elements include precipitation, temperature, humidity, sunshine and wind velocity and phenomena such as fog, frost, and hail storms. Climate cannot be considered a satisfactory indicator of actual conditions since it is based upon a vast number of elements taken as an average. Cloudburst A sudden, intense rainfall that is normally of short duration. Cloudy Cloudy means that clouds cover more than 60 percent of the sky. Coastal flood warning Issued when there is widespread coastal flooding expected within 12 hours, more than just a typical overwash. Cold In the winter, cold refers to four to seven degrees Celsius below normal.

Cold Advection (CAA) Transport of cold air into a region by horizontal winds. Cold front A narrow transition zone separating advancing colder air from retreating warmer air. The air behind a cold front is cooler and typically drier than the air it is replacing. Cold low A low pressure system with cold air mass from near the surface to all vertical levels (also called a cold core low). Cold-air-funnel A funnel cloud or (rarely) a small, relatively weak tornado that can develop from a small shower or thunderstorm when the air aloft is unusually cold (hence the name). They are much less violent than other types of tornadoes. Collar cloud Frequently used as a synonym for wall cloud, although it actually is a generally circular ring of cloud surrounding the upper portion of a wall cloud. Combined seas The combined height of swell and wind waves. Condensation The process by which water vapor becomes a liquid; the opposite of evaporation, which is the conversion of liquid to vapor. In Australia, it is described as a change from a gas to a liquid. Confluence A pattern of wind flow in which air flows inward toward an axis oriented parallel to the general direction of flow. It is the opposite of difluence.

Confluence is not the same as convergence. Winds often accelerate as they enter a confluent zone, resulting in speed divergence which offsets the (apparent) converging effect of the confluent flow. Congestus (or Cumulus congestus) A large cumulus cloud with great vertical development, usually with a cauliflower-like appearance, but lacking the characteristic anvil shaped top of a Cb (Cumulonimbus cloud). Continental air mass A dry air mass originating over a large land area. Convection The transfer of heat within the air by its movement. The term is used specifically to describe vertical transport of heat and moisture, especially by updrafts and downdrafts in an unstable atmosphere. Convergence An atmospheric condition that exists when the winds cause a horizontal net inflow of air into a specified region. Divergence is the opposite, where winds cause a horizontal net outflow of air from a specified region. Cumulonimbus Cloud A vertically developed cloud, often capped by an anvil shaped cloud. Also called a thunderstorm cloud, it is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail or gusty winds.

In Australia, it is described as a heavy, puffy, heaped, dark cloud of great vertical depth, often bringing rain. Some have a distinctive anvil shaped head. Cumulus cloud A cloud in the shape of individual detached domes, with a flat base and a bulging upper portion resembling cauliflower. In Australia, it is described as a cloud with a woolly, heaped appearance that often produces rain. Cumulus congestus A large cumulus cloud with great vertical development, usually with a cauliflower-like appearance, but lacking the characteristic anvil shaped top of a Cb (Cumulonimbus cloud). Cyclone An area of low pressure around which winds blow counterclockwise in the Northern Hemisphere. Also the term used for a hurricane in the Indian Ocean and in the Western Pacific Ocean. In Australia, it is described as atmospheric circulations that rotate clockwise in the southern hemisphere, and anti-clockwise in the northern hemisphere. Cyclones are areas of lower pressure and generally associated with stronger winds, unsettled conditions, cloudiness and rainfall. Day of the week (eg. Monday) Midnight to midnight.

Debris cloud A rotating "cloud" of dust or debris, near or on the ground, often appearing beneath a condensation funnel and surrounding the base of a tornado. Dense fog A fog in which the visibility is less than one-quarter mile. Depression A region of low atmospheric pressure that is usually accompanied by low clouds and precipitation. Dew point The temperature to which the air must be cooled for water vapor to condense and form fog or clouds. Diamond dust A fall of non-branched (snow crystals are branched) ice crystals in the form of needles, columns, or plates. Difluence A pattern of wind flow in which air moves outward (in a "fan-out" pattern) away from a central axis that is oriented parallel to the general direction of the flow. It is the opposite of confluence. Disturbance A disruption of the atmosphere that usually refers to a low pressure area, cool air and inclement weather. Downburst A strong downdraft resulting in an outward burst of damaging winds on or near the ground. Downburst winds can produce damage similar to a strong tornado. Downdraft A column of generally cool air that rapidly sinks to the ground, usually accompanied by precipitation as in a shower or thunderstorm.

Downslope wind Air that descends an elevated plain and consequently warms and dries. Occurs when prevailing wind direction is from the same direction as the elevated terrain and often produces fair weather conditions. Draft A draft is a small gusty air current that moves upward or downward abruptly; hence the terms updraft and downdraft. Drifting snow Uneven distribution of snowfall caused by strong surface winds. Drifting snow does not reduce visibility. In Canada, it is defined as snow blown to a height of less than two meters. Drizzle Small, slowly falling water droplets, with diameters between .2 and .5 millimeters. In Australia, it is defined as fairly uniform precipitation (rain) composed exclusively of very small water droplets (less than 0.5 mm in diameter) very close to one another. Drought Abnormally dry weather in a region over an extended period sufficient to cause a serious hydrological (water cycle) imbalance in the affected area. This can cause such problems as crop damage and water-supply shortage. In Australia, it is defined as the prolonged absence or marked deficiency of precipitation (rain). Dry Free from rain.

Normally used when preceding weather has also been relatively dry and dry weather is expected to continue for a day or so. Dust storm An area where high surface winds have picked up loose dust, reducing visibility to less than one-half mile. In Australia, it is described as a storm which carries large amounts of dust into the atmosphere. A basic forecast of general weather conditions three to five days in the future. Extratropical cyclone A storm that forms outside the tropics, sometimes as a tropical storm or hurricane changes. See table below for differences between extratropical and tropical cyclones. Top Fahrenheit The standard scale used to measure temperature in the United States; in which the freezing point of water is 32 degrees and the boiling point is 212 degrees. Fair Describes weather in which there is less than 4/10ths of opaque cloud cover, no precipitation, and there is no extreme visibility, wind or temperature conditions. Fall wind A strong, cold, downslope wind. Fine No rain or other precipitation (hail, snow etc.). The use of fine is generally avoided in excessively cloudy, windy, foggy or dusty conditions.

In particular note that fine means the absence of rain or other precipitation such as hail or snow - not 'good' or 'pleasant' weather. Flash flood A flood that occurs within a few hours (usually less than six) of heavy or excessive rainfall, dam or levee failure or water released from an ice jam. Flood A condition that occurs when water overflows the natural or artificial confines of a stream or river; the water also may accumulate by drainage over low-lying areas. Flood crest The highest stage or flow occurring in a flood. Flurry A flurry or snow shower is a snowfall that suddenly stops and starts and changes rapidly in intensity; the accumulation and extent of the snow are limited. Fog Water that has condensed close to ground level, producing a cloud of very small droplets that reduces visibility to less than one km (three thousand and three hundred feet). In Canada, fog is defined as a cloud at ground level, and occurs when air is cooled to its dew point and below, or when atmospheric moisture increases through evaporation from water that is warmer than the air. In the United Kingdom, fog is described to occur when visibility less than one kilometer.

In Australia, it is defined as a dense mass of small water droplets or particles in the lower atmosphere. Fogbow A rainbow that has a white band that appears in fog, and is fringed with red on the outside and blue on the inside. Forecast A forecast provides a description of the most significant weather conditions expected during the current and following days. The exact content depends upon the intended user, such as the Public or Marine forecast audiences. Freeze Occurs when the surface air temperature is expected to be 32 degrees Fahrenheit or below over a widespread area for a significant period of time. In Australia, the term “freeze” is defined as the change from a liquid to a solid. Freezing The change in a substance from a liquid to a solid state. Freezing drizzle Drizzle that falls in liquid form and then freezes upon impact with the ground or an item with a temperature of 32 degrees Fahrenheit or less, possibly producing a thin coating of ice. Even in small amounts, freezing drizzle may cause traveling problems. Freezing fog A suspension of numerous minute ice crystals in the air, or water droplets at temperatures below zero degrees Celsius, based at the Earth's surface, which reduces horizontal visibility; also called ice fog.

Freezing level The altitude in the atmosphere where the temperature drops to 32F. Freezing rain Rain that freezes on objects such as trees, cars and roads, forming a coating or glaze of ice. Temperatures at higher levels are warm enough for rain to form, but surface temperatures are below 32 degrees Fahrenheit, causing the rain to freeze on impact. In Canada, freezing rain is described to occur when the air temperature is below zero Celsius near the ground but above zero Celsius higher up. Front The boundary or transition zone between two different air masses. The basic frontal types are cold fronts, warm fronts and occluded fronts. Frost The formation of thin ice crystals on the ground or other surfaces. Frost develops when the temperature of the exposed surface falls below 32 degrees Fahrenheit and water vapor is deposited as a solid. Frost point When the temperature to which air must be cooled to in order to be saturated is below freezing. Fujita scale System developed by Dr Theodore Fujita to classify tornadoes based on wind damage. Scale is from F0 for weakest to F5 for strongest tornadoes. Fujiwhara effect The Fujiwhara effect describes the rotation of two storms around each other.

Funnel cloud A rotating, cone-shaped column of air extending downward from the base of a thunderstorm but not touching the ground. When it reaches the ground it is called a tornado. Sustained wind speeds from 34 to 47 knots (39 to 54 mph). Glaze a layer or coating of ice that is generally smooth and clear, and forms on exposed objects by the freezing of liquid raindrops. Global warming A theory that increased concentrations of greenhouse gases are causing an elevation in the Earth's surface temperature. Good visibility More than 10 kilometers. Greenhouse effect The warming of the atmosphere by the trapping of longwave radiation (heat) being radiated to space. The gases most responsible for this effect are water vapor and carbon dioxide. Ground fog Shallow fog (less than twenty feet deep) produced over the land by the cooling of the lower atmosphere as it comes in contact with the ground. Also known as radiation fog. Gust A brief sudden increase in wind speed. Generally the duration is less than 20 seconds and the fluctuation greater than 10 miles per hour. In Canada, gust is defined as a sudden, brief increase in wind speed that generally lasts less than 20 seconds.

In Australia, gust is defined as any sudden increase of wind of short duration, usually a few seconds. Gustnado Gust front tornado. A small tornado, usually weak and short-lived, that occurs along the gust front of a thunderstorm. Often it is visible only as a debris cloud or dust whirl near the ground. Top Hail Precipitation in the form of balls or irregular lumps of ice produced by liquid precipitation, freezing and being coated by layers of ice as it is lifted and cooled in strong updrafts of thunderstorms. Haze Fine dust or salt particles in the air that reduce visibility. In Canada, haze is defined to consist of fine particles of dust and pollution suspended in the atmosphere, and is distinguished from fog by its bluish or yellowish tinge. Heat balance The equilibrium existing between the radiation received and emitted by a planetary system. Heat index An index that combines air temperature and humidity to give an apparent temperature (how hot it feels). Heat island A dome of elevated temperatures over an urban area caused by the heat absorbed by structures and pavement. Heat lightning Lightning that can be seen, but is too far away for the thunder to be heard. Heat wave A period of abnormally hot weather lasting several days.

Heavy snow Depending on the region of the USA, this generally means that four or more inches of snow has accumulated in 12 hours, or six or more inches of snow in 24 hours. Heavy snow warning Older terminology replaced by winter storm warning for heavy snow. Issued when seven or more inches of snow or sleet is expected in the next 24 hours. A warning is used for winter weather conditions posing a threat to life and property. Heavy surf the result of large waves breaking on or near the shore resulting from swells or produced by a distant storm. High An area of high pressure, usually accompanied by anticyclonic and outward wind flow. Also known as an anticyclone. In Canada, a high is described as an area of high atmospheric pressure with a closed, clockwise movement of air. High cloud High risk (of severe thunderstorm) Severe weather is expected to affect more than 10 percent of the area. High wind warning Issued when sustained winds from 40 to 73 mph are expected for at least one hour; or any wind gusts are expected to reach 58 miles per hour or more.

High wind watch Issued when conditions are favorable for the development of high winds over all of or part of the forecast area but the occurrence is still uncertain. The criteria of a high wind watch are listed under the high wind warning and should include the area affected, the reason for the watch and the potential impact of the winds. Hot or very warm In summer, hot or very warm means more than seven degrees Celsius above normal. Hot spot Typically large areas of pavement, these "hot spots" are heated much quicker by the sun than surrounding grasses and forests. As a result, air rises upwards from the relatively hot surface of the pavement, reaches its condensation level, condenses, and forms a cloud above the "hot spot". Humidity The amount of water vapor in the atmosphere. In Canada, it is described as the amount of moisture in the air. Hurricane A severe tropical cyclone with sustained winds over 74 miles per hour (64 knots). Normally applied to such storms in the Atlantic Basin and the Pacific Ocean east of the International Date Line. Hygrometer Top Ice crystals Ice crystals are tiny sprinkles that sparkle in the sunshine like diamond dust and hang in the air.

Ice fog A suspension of numerous minute ice crystals in the air, or water droplets at temperatures below zero degrees Celsius, based at the Earth's surface, which reduces horizontal visibility. Usually occurs at -20 degrees Fahrenheit and below. Ice pellets Precipitation of transparent or translucent pellets of ice, which are round or irregular, rarely conical, and which have a diameter of 0.2 inch (five millimeters), or less. There are two main types. Hard grains of ice consisting of frozen raindrops and pellets of snow encased in a thin layer of ice. Ice storm Liquid rain falling and freezing on contact with cold objects creating ice build-ups of 1/4th inch or more that can cause severe damage. Ice storm warning Older terminology replaced by winter storm warning for severe icing. Issued when 1/2 inch or more of accretion of freezing rain is expected. This may lead to dangerous walking or driving conditions and the pulling down of power lines and trees. A warning is used for winter weather conditions posing a threat to life and property. Indian summer An unseasonably warm period near the middle of autumn, usually following a substantial period of cool weather.

Inflow bands (or feeder bands) Bands of low clouds, arranged parallel to the low-level winds and moving into or toward a thunderstorm. Insolation Incoming solar radiation. Solar heating; sunshine. Instability A state of the atmosphere in which convection takes place spontaneously, leading to cloud formation and precipitation. Intermittent rain Intermittent rain stops and starts repeatedly, although not as abruptly or as frequently as showers. Intertropical Convergence Zone (ITCZ) The region where the northeasterly and southeasterly trade winds converge, forming an often continuous band of clouds or thunderstorms near the equator. Inversion An increase in temperature with height. The reverse of the normal cooling with height in the atmosphere. Temperature inversions trap atmospheric pollutants in the lower troposphere, resulting in higher concentrations of pollutants at ground levels than would usually be experienced. Iridescence Brilliant patches of green or pink sometimes seen near the edges of high- or medium-level clouds. Isentropic lift Lifting of air that is traveling along an upward-sloping isentropic surface. Situations involving isentropic lift often are characterized by widespread stratiform clouds and precipitation. Top Jet stream Strong winds concentrated within a narrow band in the upper atmosphere.

It normally refers to horizontal, high-altitude winds. The jet stream often "steers" surface features such as front and low pressure systems. Wind blowing down an incline, such as down a hillside; downslope wind. Katafront A front (usually a cold front) at which the warm air descents the frontal surface. Killing frost Frost severe enough to end the growing season. This usually occurs at temperatures below 28 degrees Fahrenheit. In Canada, a killing frost is described as a frost severe enough to destroy annual plants and new growth on trees (in the spring) or to end the growing season (in the fall). Knot A measure of speed. It is one nautical mile per hour (1.15 miles per hour). A nautical mile is one minute of one degree of latitude. A cooling of the equatorial waters in the Pacific Ocean. Land breeze A wind that blows from the land towards a body of water. Also known as an offshore breeze. It occurs when the land is cooler than the water. Late From sunset (winter), from two hours before sunset (summer). Leeward Situated away from the wind; downwind - opposite of windward.

Left Mover A thunderstorm which moves to the left relative to the steering winds and to other nearby thunderstorms; often the northern part of a splitting storm. Lifting The forcing of air in a vertical direction by an upslope in terrain or by the movement of a denser air mass. Lifting condensation level The level in the atmosphere where a lifted air parcel reaches its saturation point, and as a result, the water vapor within condenses into water droplets. Lightning Any form of visible electrical discharges produced by thunderstorms. Likely In probability of precipitation statements, the equivalent of a 60 or 70 percent chance. Low An area of low pressure, usually accompanied by cyclonic and inward wind flow. Also known as a cyclone. Low cloud Stratus, stratocumulus, cumulus and cumulonimbus. Low-level jet Top Mainly cloudy More than half cloud cover but with some breaks in the cloud. It can also be described as cloudy with some sunny periods. Mainly sunny Mainly sunny means sunny with some cloudy periods. Mammatus (or mamma clouds) These clouds appear as hanging, rounded protuberances or pouches on the under-surface of a cloud.

With thunderstorms, mammatus are seen on the underside of the anvil. These clouds do not produce tornadoes, funnels, hail, or any other type of severe weather, although they often accompany severe thunderstorms. Maritime air mass An air mass that forms over water. It is usually humid, and may be cold or warm. Maximum temperature The highest temperature during a specified time period. Mean temperature The average of a series of temperatures taken over a period of time, such as a day or a month. Medium cloud Altostratus, altocumulus and nimbostratus. Meteorology The study of the physics, chemistry, and dynamics of the atmosphere and the direct effects of the atmosphere upon the Earth's surface, the oceans, and life in general. Mild In winter, mild refers to four to seven degrees Celsius above normal. Minimum temperature The lowest temperature during a specified time period. Mist Consists of microscopic water droplets suspended in the air, which produces a thin grayish veil over the landscape. It reduces visibility to a lesser extent than fog. In Australia, it is described as similar to fog, but visibility remains more than a kilometer.

Moderate risk Severe thunderstorms are expected to affect between five and 10 percent of the area. Moderate visibility Five to 10 kilometers’ visibility. Monsoon A persistent seasonal wind, often responsible for seasonal precipitation regime. It is most commonly used to describe meteorological changes in southern and eastern Asia. Morning Sunrise to noon or midnight to noon depending on context. Mountain breeze System of winds that blow downhill during the night. Muggy Colloquially descriptive of warm and especially humid weather. Multivortex tornado A tornado in which two or more condensation funnels or debris clouds are present at the same time, often rotating about a common center or about each other. Multiple-vortex tornadoes can be especially damaging. Mushroom No weather information available for this time slot. Normal The long-term average value of a meteorological element for a certain area. For example, "temperatures are normal for this time of year" Usually averaged over 30 years. Top Offshore breeze A wind that blows from the land towards a body of water. Also known as a land breeze. Offshore forecast A marine weather forecast for the waters between 60 and 250 miles off the coast.

Onshore breeze A wind that blows from a body of water towards the land. Also known as a sea breeze. Outflow Air that flows outward from a thunderstorm. Outflow winds Winds that blow down fjords and inlets from the land to the sea. Overcast Sky condition when greater than 9/10ths of the sky is covered by clouds. In Canada overcast means grey and dull skies, with extensive cloud cover. Overrunning A condition that exists when a relatively warm air mass moves up and over a colder and denser air mass on the surface. The result is usually low clouds, fog and steady, light precipitation. Ozone A form of oxygen in which the molecule is made of three atoms instead of the usual two. Ozone is usually found in the stratosphere, and responsible for filtering out much of the sun's ultraviolet radiation. It is also a primary component of smog. Ozone hole Top Partly cloudy Sky condition when between 3/10ths and 7/10ths of the sky is covered. Used more frequently at night. In the United Kingdom, it is defined as less than half cloud cover. Partly sunny Similar to partly cloudy. Used to emphasize daytime sunshine.

Permafrost A soil layer below the surface of tundra regions that remains frozen permanently. Polar air A mass of very cold, very dry air that forms in polar regions. Polar front The semi-permanent, semi-continuous front that encircles the northern hemisphere separating air masses of tropical and polar origin. Polar Stratospheric Clouds (PSCs) High altitude clouds that form in the stratosphere above Antarctica during the Southern Hemisphere winter. Their presence seems to initiate the ozone loss experienced during the ensuing southern hemisphere spring. Polar vortex A circumpolar wind circulation which isolates the Antarctic continent during the cold Southern Hemisphere winter, heightening ozone depletion. Poor visibility One to five kilometers’ visibility. POP Probability of Precipitation. Probability forecasts are subjective estimates of the chances of encountering measurable precipitation at some time during the forecast period. Popcorn convection Clouds, showers and thundershowers that form on a scattered basis with little or no apparent organization, usually during the afternoon in response to diurnal heating. Precipitation Liquid or solid water that falls from the atmosphere and reaches the ground. Pressure The force exerted by the interaction of the atmosphere and gravity. Also known as atmospheric pressure.

Pressure change The net difference between pressure readings at the beginning and ending of a specified interval of time. Pressure falling rapidly A decrease in station pressure at a rate of 0.06 inch of mercury or more per hour which totals 0.02 inches or more. Pressure rising rapidly An increase in station pressure at a rate of 0.06 inch of mercury or more per hour which totals 0.02 inches or more. Pressure tendency The character and amount of atmospheric pressure change during a specified period of time, usually the three-hour period preceding an observation. Prevailing westerlies Winds in the middle latitudes (approximately 30 degrees to 60 degrees) that generally blow from west to east. Prevailing wind The direction from which the wind blows most frequently in any location. Pulse storm A thunderstorm within which a brief period (pulse) of strong updraft occurs, during and immediately after which the storm produces a short episode of severe weather. These storms generally are not tornado producers, but often produce large hail and/or damaging winds. See overshooting top, cyclic storm. Top Qualitative forecasts Forecasts that provide only a categorical value for the predicted variable.

Examples of this include “rain/no rain” and “cloudy/partly cloudy”. Quantitative forecasts Forecasts in which the “amount” of the forecast variable is specified. Quantitative precipitation forecast (QPF) A forecast of rainfall, snowfall or liquid equivalent of snowfall. Quasi-biennial oscillation (QBO) Periodic variation in the direction, either easterly or westerly, of tropical lower stratospheric winds. The direction changes every 26 months. Quasi-nonhydrostatic (QNH) Pilots, air traffic control (ATC) and low frequency weather beacons use this pressure setting to refer to the barometric altimeter setting that causes the altimeter to read altitude above mean sea level within a certain defined region. Quasi-stationary front A front which is nearly stationary or moves very little since the last synoptic position. Also known as a stationary front. Top Radar An instrument used to detect precipitation by measuring the strength of the electromagnetic signal reflected back. (RADAR= Radio Detection and Ranging). Radiation Energy emitted in the form of electromagnetic waves. Radiation has differing characteristics depending upon the wavelength.

Radiation from the Sun has a short wavelength (ultra-violet) while energy re-radiated from the Earth's surface and the atmosphere has a long wavelength (infra-red). Radiation fog Fog produced over the land by the cooling of the lower atmosphere as it comes in contact with the ground. Also known as ground fog. Rain Liquid water droplets that fall from the atmosphere, having diameters greater than drizzle (0.5 mm). In Canada the term "rain", used alone, means liquid precipitation of significant duration and extent. Rain gauge An instrument used to measure rainfall amounts. Rain showers Rain showers stop and start suddenly and vary widely in intensity, and are gone in less than an hour. Rainbow Optical phenomena when light is refracted and reflected by moisture in the air into concentric arcs of color. Raindrops act like prisms, breaking the light into the colors of a rainbow, with red on the outer, and blue on the inner edge. Relative humidity The amount of water vapor in the air, compared to the amount the air could hold if it was totally saturated. It is expressed as a percentage. Return flow South winds on the back (west) side of an eastward-moving surface high pressure system.

Return flow over the central and eastern United States typically results in a return of moist air from the Gulf of Mexico (or the Atlantic Ocean). Ridge An elongated area of high pressure in the atmosphere. Opposite of a trough. River flood warning Issued when main stem rivers are expected to reach a level above flood stage. Roll cloud A relatively rare, low-level horizontal, tube-shaped accessory cloud completely detached from the cumulonimbus base. When present, it is located along the gust front and most frequently observed on the leading edge of a line of thunderstorms. The roll cloud will appear to be slowly "rolling" about its horizontal axis. Roll clouds are not and do not produce tornadoes. Top Sandstorm Particles of sand carried aloft by a strong wind. The sand particles are mostly confined to the lowest ten feet, and rarely rise more than fifty feet above the ground. Saturation A condition of the atmosphere in which a certain volume of air holds the maximum water vapor it can hold at a specific temperature. Scattered A cloud layer that covers between 3/8ths and 1/2 of the sky.

Scud clouds Small, ragged, low cloud fragments that are unattached to a larger cloud base and often seen with and behind cold fronts and thunderstorm gust fronts. Such clouds generally are associated with cool moist air, such as thunderstorm outflow. Sea breeze A wind that blows from a sea or ocean towards a land mass. Also known as an onshore breeze. It occurs when the land is warmer than the water. Sea-level pressure The pressure value obtained by the theoretical reduction or increase of barometric pressure to sea-level. Secondary cold front A front that follows a primary cold front and ushers in even colder air. Severe thunderstorm A strong thunderstorm with wind gusts in excess of 58 mph (50 knots) and/or hail with a diameter of 3/4 inch or more. Shallow fog Fog in which the visibility at 6 feet above ground level is 5/8ths of a mile or more. Shelf-cloud A low-level horizontal accessory cloud that appears to be wedge-shaped as it approaches. It is usually attached to the thunderstorm base and forms along the gust front. Short-fuse warning A warning issued by the National Weather Service for a local weather hazard of relatively short duration.

Short-fuse warnings include tornado warnings, severe thunderstorm warnings, and flash flood warnings. Tornado and severe thunderstorm warnings typically are issued for periods of an hour or less, flash flood warnings typically for three hours or less. Shower Precipitation that is intermittent, both in time, space or intensity. Sky condition The state of the sky in terms of such parameters as sky cover, layers and associated heights, ceiling, and cloud types. Sleet Rain drops that freeze into ice pellets before reaching the ground. Sleet usually bounces when hitting a surface and does not stick to objects. Forms when snow enters a warm layer of air above the surface and melts and then enters a deep layer of sub freezing air near the surface and refreezes. In Australia, sleet refers to a mixture of rain and snow or falling snow that is melting into rain. Slight chance In probability of precipitation statements, usually equivalent to a 20 percent chance. Slight risk (of severe thunderstorms) Severe thunderstorms are expected to affect between two and five percent of the area. A slight risk generally implies that severe weather events are expected to be isolated.

Smog Pollution formed by the interaction of pollutants and sunlight (photochemical smog), usually restricting visibility, and occasionally hazardous to health. Smoke A suspension in the air of small particles produced by combustion. A transition to haze may occur when smoke particles have traveled great distances (25 to 100 statute miles or more) and when the larger particles have settled out and the remaining particles have become widely scattered through the atmosphere. Snow Frozen precipitation composed of ice particles in complex hexagonal patterns. Snow forms in cold clouds by the direct transfer of water vapor to ice. Snow burst Very intense shower of snow, often of short duration, that greatly restricts visibility and produces periods of rapid snow accumulation. Snow flurries Light snow showers, usually of an intermittent nature and short duration with no measurable accumulation. Snow grains Light snow showers, usually of an intermittent nature and short duration with no measurable accumulation. In Canada, Snow grains are described as minute, white and opaque grains of ice. When they hit hard ground, they do not bounce or shatter. They usually fall in very small quantities, and never in the form of a shower. Snow pellets Precipitation of white, opaque grains of ice. The grains are round or sometimes conical.

Diameters range from about 0.08 to 0.2 inch (2 to 5 mm). In Canada, snow pellets are brittle and easily crushed; when they fall on hard ground, they bounce and often break up. They always occur in showers and are often accompanied by snowflakes or rain drops, when the surface temperature is around zero degrees Celsius. Snow shower Snow falling at varying intensities for brief periods of time. Some accumulation is possible. Snow squalls Intense, but of limited duration, periods of moderate to heavy snowfall, accompanied by strong, gusty surface winds and possible lightning. In Canada, it is described that a snow squall brings strong winds, flurries and poor visibility. Snowfall The depth of new snow that has accumulated since the previous day or since the previous observation. Snowflake White ice crystals that have combined in a complex branched hexagonal form. Special marine warning Issued for brief or sudden occurrence of sustained wind or frequent gusts of 34 knots or more. This is usually associated with severe thunderstorms or waterspouts.

Spray An ensemble of water droplets torn by the wind from an extensive body of water, generally from the crests of waves, and carried up into the air in such quantities that it reduces the horizontal visibility. Squall A strong wind characterized by a sudden onset in which the wind speed increases at least 16 knots and is sustained at 22 knots or more for at least one minute. In Canada, a squall is defined as a strong, sudden wind which generally lasts a few minutes then quickly decreases in speed. In Australia, it is described as a sudden increase of the mean wind speed which lasts for several minutes at least before the mean wind returns to near its previous value. Stability An indication of how easily a parcel of air is lifted. If the air is very stable it is difficult to make the parcel rise. If the air is very unstable the parcel may rise on its own once started. Stable air Air with little or no tendency to rise, usually accompanied by clear dry weather. Steam fog Fog that is formed when water vapor is added to air which is much colder than the vapor's source. This is most common when very cold air drifts across relatively warm water.

Steering winds (steering currents) A prevailing synoptic scale flow which governs the movement of smaller features embedded within it. Storm In marine usage, winds 48 knots (55 miles per hour) or greater. Storm surge A rise of the sea level alone the shore that builds up as a storm (usually a hurricane) moves over water. It is a result of the winds of the storm and low atmospheric pressures. Storm warning A marine wind warning for sustained winds greater of 48 knots (55 miles per hour) or more from a non-tropical system. Straight line winds Thunderstorm winds most often found with the gust front. Subtropical storm A low pressure system that develops in subtropical waters (north of 20 north degrees latitude) and initially has non-tropical features (see table below for a list of tropical features) but does have some element of a tropical cyclone's cloud structure (located close to the center rather than away from the center of circulation). Sunny Sunny or a few clouds means that less than half the sky has clouds. Supercell A severe thunderstorm whose updrafts and downdrafts are in near balance allowing the storm to maintain itself for several hours.

Supercells often produce large hail and tornadoes. Supersaturation Top Temperature A measure of the warmth or coldness of an object or substance with reference to a standard value. Thunder The sound caused by a lightning stroke as it heats the air and causes it to rapidly expand. Thunderstorm A storm with lightning and thunder produced by a Cumulonimbus cloud, usually producing gusty winds, heavy rain and sometimes hail. In Australia, they are described to be usually short-lived and hit on only a small area. Tilted storm or tilted updraft A thunderstorm or cloud tower which is not purely vertical but instead exhibits a slanted or tilted character. It is a sign of vertical wind shear, a favorable condition for severe storm development. Today Sunset to midnight. Tornado A violent rotating column of air, in contact with the ground, pendant from a cumulonimbus cloud. A tornado does not require the visible presence of a funnel cloud. It has a typical width of tens to hundreds of meters and a lifespan of minutes to hours. Trade winds Persistent tropical winds that blow from the subtropical high pressure centers towards the equatorial low. They blow northeasterly in the northern hemisphere.

Tropical storm An organized low pressure system in the tropics with wind speeds between 38 and 74 miles per hour. In Australia, it is a term used in the northern hemisphere for a tropical cyclone. Tropical storm warning A warning issued when sustained winds of 39 to 73 miles per hour (34 to 63 knots) are expected within 24 hours. Trough A warning issued when sustained winds of 39 to 73 mph (34 to 63 knots) are expected within 24 hours. In Canada, it is described as an elongated area of relatively low pressure extending from the centre of a region of low pressure. Trough A warning issued when sustained winds of 39 to 73 mph (34 to 63 knots) are expected within 24 hours. In Canada, it is described as an elongated area of relatively low pressure extending from the centre of a region of low pressure. Turbulence A warning issued when sustained winds of 39 to 73 miles per hour (34 to 63 knots) are expected within 24 hours. Twister A colloquial term for a tornado.

Typhoon A hurricane that forms in the Western Pacific Ocean. It is a term used in Australia for a tropical cyclone in the northwestern Pacific with maximum winds above 117 kilometers per hour (63 knots). In summer, warm refers to four to seven degrees Celsius above normal. Warm front A narrow transitions zone separating advancing warmer air from retreating cooler air. The air behind a warm front is warmer and typically more humid than the air it is replacing. In Canada, it is defined as the trailing edge of a retreating cold air mass and moves in such a way that the warmer air replaces the colder air. Wave In meteorology any pattern identifiable on a weather map that has a cyclic pattern or a small cyclonic circulation in the early stages of development that moves along a cold front. In Canada, A wave, in meteorology, is the intersection of warm and cold fronts. Weather State of the atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness. Also, weather is the meteorological day-to-day variations of the atmosphere and their effects on life and human activity. It includes temperature, pressure, humidity, clouds, wind, precipitation and fog.

Wind Wind is the horizontal movement of air relative to the earth's surface and is caused by variations in temperature and pressure (for instance, air rises as it warms and a cool breeze moves in to take the place of the rising air.) Wind is also known as moving air. Wind chill The additional cooling effect resulting from wind blowing on bare skin. The wind chill is based on the rate of heat loss from exposed skin caused by the combined effects of wind and cold. The (equivalent) wind chill temperature is the temperature the body "feels" for a certain combination of wind and air temperature. Winter storm A heavy snow event. A snow accumulation of more than six inches in 12 hours or more than 12 inches in 24 hours. Winter storm warning Issued when seven or more inches of snow or sleet is expected in the next 24 hours, or 1/2 inch or more of accretion of freezing rain is expected. A warning is used for winter weather conditions posing a threat to life and property.

Question: A 'pea-souper' is which type of weather condition?
Answer: Fog