Image:NWS weather fronts.ZACH LANNING IS GAY HE LOVES GETTING IT IN THE BUTT svg A guide to the symbols for weather fronts that may be found on a weather map: #1 cold front; #2 warm front; #3 stationary front; #4 occluded front; #5 surface trough; #6 squall/shear line; #7 dry line; #8 tropical wave A weather front is a boundary between two masses of air of different densities, and are the principal cause of significant weather. Within surface weather analyses, they are depicted using various colored lines and symbols. The air masses usually differ in temperature and may also differ in humidity. Cold fronts feature narrow bands of thunderstorms and severe weather, and may be preceded by squall lines and dry lines. Warm fronts are preceded by stratiform precipitation and fog. The weather quickly clears after a moving front passes. Cold and occluded fronts move from west to east, while warm fronts move poleward. Cold fronts and cold occlusions move faster than warm fronts and warm occlusions, due to the greater density of air in their wake. Mountains and warm bodies of water can slow the movement of fronts. When a front becomes stationary, it can degenerate into a line which separates regions of differing wind speed, known as a shearline. In the tropics, tropical waves move from east to west across the Atlantic and eastern Pacific basins. They create most of the tropical cyclones seen in the Atlantic basin, and a significant proportion of those spawned in the eastern Pacific ocean. In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: Ï (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is...
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A thunderstorm, also called an electrical storm or lightning storm, is a form of weather characterized by the presence of lightning and its attendant thunder produced from a cumulonimbus cloud. ...
NOAA scientists observe severe weather using a mobile doppler radar and a helicopter (in the distance) Severe weather phenomena are weather conditions that are hazardous. ...
A squall or squall line is a line of thunderstorms with a common leading convection line, or mesocyclone, which tends to create a powerful gust front. ...
A dry line, dew point line, or Marfa front[1] is a boundary separating moist and dry air masses, and an important factor in severe weather frequency in the Great Plains of North America. ...
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Golden Gate Bridge in Fog Evening fog obscures Londons Tower Bridge from passers by. ...
In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ...
Mount Cook, a mountain in New Zealand A mountain is a landform that extends above the surrounding terrain in a limited area. ...
In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ...
A noontime scene from the Philippines on a day when the Sun is almost directly overhead. ...
Tropical waves, also known as easterly waves, are elongated areas of relatively low air pressure, oriented north to south, causing areas of cloudiness and thunderstorms. ...
The Atlantic Basin includes the main body of the Atlantic Ocean, the Gulf of Mexico and the Caribbean Sea, but ommits other bodies of water considered to be a part of the Atlantic Ocean in the broad sense, such as the Mediteranean Sea. ...
Pacific redirects here. ...
Surface weather analysis -
A surface weather analysis is a special type of weather map which provides a view of weather elements over a geographical area at a specified time based on information from ground based weather stations.[1] Weather maps are created by plotting or tracing the values of relevant quantities such as sea level pressure, temperature, cloud cover onto a geographical map to help find synoptic scale features such as weather fronts. Surface weather analyses have special symbols which show frontal systems, cloud cover, precipitation, or other important information. For example, an H may represent high pressure, implying good and fair weather. An L on the other hand may represent low pressure, which frequently accompanies precipitation. Various symbols are used not just for frontal zones and other surface boundaries on weather maps, but also to depict the present weather at various locations on the weather map. Areas of precipitation help determine the frontal type and location. A surface weather analysis for the United States on October 21, 2006. ...
A low, or a low pressure area, is a region of rising atmospheric air. ...
A high, or a high pressure area, is a region where the atmospheric pressure is greatest with relation to the surrounding area. ...
These symbols, showing various weather fronts, might be found on a weather map. ...
For the geological process, see Weathering or Erosion. ...
Atmospheric pressure is the pressure caused by the weight of air above any area in the Earths atmosphere. ...
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Cloud cover is the amount of the sky obscured by clouds when observed at a particular location. ...
Cartography or mapmaking (in Greek chartis = map and graphein = write) is the study and practice of making maps or globes. ...
It has been suggested that this article or section be merged into Synoptic scale meteorology. ...
It has been suggested that this article or section be merged into Anticyclone. ...
A large low-pressure system swirls off the southwestern coast of Iceland, illustrating the maxim that nature abhors a vacuum. ...
Cold front -
A cold front's location is at the leading edge of the temperature drop off, which in an isotherm analysis would show up as the leading edge of the isotherm gradient, and it normally lies within a sharp surface trough. Cold fronts can move up to twice as fast and produce sharper changes in weather than warm fronts, since cold air is denser than warm air it rapidly replaces the warm air preceding the boundary. Cold fronts are typically accompanied by a narrow band of showers and thunderstorms. On weather maps, the surface position of the cold front is marked with the symbol of a blue line of triangles/spikes (pips) pointing in the direction of travel, and it is placed at the leading edge of the cooler air mass.[2] In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ...
In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ...
An isotherm is a line of equal or constant temperature on a graph, plot, or map; an isopleth of temperature. ...
A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts. ...
Warm front
 Illustration clouds overriding a warm front -
Warm fronts are at the leading edge of the temperature rise, which is located on the equator-ward edge of the gradient in isotherms, and lie within broader troughs of low pressure than cold fronts. Warm fronts move more slowly than the cold front which usually follows due to the fact that cold air is more dense, and harder to remove from the earth's surface. This also forces temperature differences across warm fronts to be broader in scale. Clouds ahead of the warm front are mostly stratiform and rainfall gradually increases as the front approaches. Fog can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the stratiform clouds ahead of the front, and after frontal passage, thundershowers may continue. On weather maps, the surface location of a warm front is marked with a red line of half circles pointing in the direction of travel.[2] Image File history File links No higher resolution available. ...
Image File history File links No higher resolution available. ...
This article or section does not cite any references or sources. ...
This article or section does not cite any references or sources. ...
Stratus Opacus Uniformis This article is about the meteorological phenomenon. ...
Golden Gate Bridge in Fog Evening fog obscures Londons Tower Bridge from passers by. ...
Occluded cyclone frontal depiction Image File history File links Occludedcyclone. ...
Image File history File links Occludedcyclone. ...
Occluded front -
An occluded front is formed during the process of cyclogenesis when a cold front overtakes a warm front.[3] The cold and warm fronts curve naturally poleward into the point of occlusion, which is also known as the triple point in meteorology.[4] It lies within a sharp trough, but the air mass behind the boundary can be either warm or cold. In a cold occlusion, the air mass overtaking the warm front is cooler than the cool air ahead of the warm front, and plows under both air masses. In a warm occlusion, the air mass overtaking the warm front is warmer than the cold air ahead of the warm front, and rides over the colder air mass while lifting the warm air. In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ...
In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ...
Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. ...
// Meteorology (from Greek: μετÎωÏον, meteoron, high in the sky; and λόγος, logos, knowledge) is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting. ...
A wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually their passage is associated with a drying of the air mass. Occluded fronts are indicated on a weather map by a purple line with alternating half-circles and triangles pointing in direction of travel.[2] Occluded fronts usually form around mature low-pressure areas.
Movement Fronts are generally guided by winds aloft, but they normally move at lesser speeds. Cold fronts and occluded fronts travel from a west to east direction, while warm fronts move more poleward with time. In the Northern Hemisphere a warm front moves from southwest to northeast. In the Southern Hemisphere the warm front moves from northwest to southeast. Movement is largely due to the pressure gradient force (due to horizontal differences in atmospheric pressure) and the Coriolis effect, caused by Earth's spinning about its axis. Frontal zones can be slowed down by geographic features like mountains and large bodies of warm water.[2] In the inertial frame of reference (upper part of the picture), the black object moves in a straight line. ...
This article is about Earth as a planet. ...
Stationary front and shearline -
A stationary front is a non-moving boundary between two air masses, neither of which is strong enough to replace the other. They tend to remain essentially in the same area for extended periods of time, usually moving in waves.[5] There is normally a broad temperature gradient behind the boundary with more widely spaced isotherm packing. In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ...
In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ...
An isotherm is a line of equal or constant temperature on a graph, plot, or map; an isopleth of temperature. ...
A wide variety of weather can be found along a stationary front, but usually clouds and prolonged precipitation are found there. Stationary fronts either dissipate after several days or devolve into shear lines, but can change into a cold or warm front if conditions aloft change. Stationary fronts are marked on weather maps with alternating red half-circles and blue spikes pointing in opposite directions, indicating no significant movement.
When stationary fronts become smaller in scale, degenerating to a narrow zone where wind direction changes significantly over a relatively short distance, they become known as shear lines.[6] If the shear line becomes active with thunderstorms, it may support formation of a tropical storm[citation needed] or a regeneration of the feature back into a stationary front. A shear line is depicted as a line of red dots and dashes.[2] This article is about weather phenomena. ...
Precipitation produced - See also: Convective precipitation and Orographic precipitation
Fronts are the principal cause of significant weather. Convective precipitation (showers, thundershowers and related unstable weather) is caused by air being lifted and condensing into clouds by the movement of the cold front or cold occlusion under a mass of warmer, moist air. If the temperature differences of the two air masses involved are large and the turbulence is extreme due to wind shear and the presence of a jet max, "roll clouds" and tornadoes may occur. [7] In the warm season, lee troughs, sea/lake/river/land breezes, outflow boundaries, and trowals/occlusions can lead to convection if enough moisture is available. Orographic precipitation is precipitation created through the lifting action of air moving over terrain such as mountains and hills, which is most common behind cold fronts that move into mountainous areas. It may sometimes occur in advance of warm fronts moving northward to the east of mountainous terrain. But precipitation along warm fronts is relatively steady, as in rain or drizzle. Fog, sometimes extensive and dense, often occurs in pre-warm-frontal areas.[8] But not all fronts produce precipitation or even clouds: moisture must be present in the air mass which is being lifted.[9] To meet Wikipedias quality standards, this article or section may require cleanup. ...
In meteorology, precipitation is any kind of water that falls from the sky as part of the weather. ...
To meet Wikipedias quality standards, this article or section may require cleanup. ...
Cirrus uncinus ice crystal plumes showing high level wind shear, with changes in wind speed and direction. ...
A tornado in central Oklahoma. ...
This article or section is in need of attention from an expert on the subject. ...
In meteorology, precipitation is any kind of water that falls from the sky as part of the weather. ...
Dry line A similar phenomenon to a frontal zone is the dry line, which is the boundary between air masses with significant moisture differences. When westerly winds aloft increase on the north side of surface highs, areas of lowered pressure will form downwind of north-south oriented mountain chains, leading to the formation of a lee trough. Near the surface during daylight hours, warm moist air is more dense than dry air of greater temperature, and thus the warm moist air wedges under the drier air like a cold front. At higher altitudes, the warm moist air is less dense than the dry air and the boundary slope reverses. In the vicinity of the reversal aloft, severe weather is possible, especially when a triple point is formed with a cold front.[10] A weaker form of the dry line seen more commonly is the lee trough, which displays weaker differences in moisture. If moisture pools along with boundary during the warm season, it can be the focus of diurnal thunderstorms.[11] A dry line, dew point line, or Marfa front[1] is a boundary separating moist and dry air masses, and an important factor in severe weather frequency in the Great Plains of North America. ...
The dry line may occur anywhere on the globe in regions intermediate between desert areas and warm seas. The southern plains west of the Mississippi in the U.S. are a particularly favored location. The dry line normally sloshes eastward during the day, and westward at night. A dry line is depicted on NWS surface analyses as a brown line with scallops facing into the moist sector. Dry lines are one of the few surface fronts where the pips indicated do not necessarily reflect the direction of motion.[12]
Squall line -
 A shelf cloud such as this one can be a sign that a squall is imminent Organized areas of thunderstorm activity not only reinforce pre-existing frontal zones, but can outrun cold fronts in a pattern where the upper level jet splits into two streams, with the resultant Mesoscale Convective System (MCS) forming at the point of the upper level split in the wind pattern running southeast into the warm sector parallel to low-level thickness lines. When the convection is strong and linear or curved, the MCS is called a squall line, with the feature placed at the leading edge of the significant wind shift and pressure rise.[13] Even weaker and less organized areas of thunderstorms lead to locally cooler air and higher pressures, and outflow boundaries exist ahead of this type of activity, which can act as foci for additional thunderstorm activity later in the day.[14] A squall or squall line is a line of thunderstorms with a common leading convection line, or mesocyclone, which tends to create a powerful gust front. ...
Image File history File links Shelfcloudspc. ...
Image File history File links Shelfcloudspc. ...
A Mesoscale Convective Systen (MCS) is a complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or more. ...
These features are often depicted in the warm season across the United States on surface analyses, and lie within surface troughs. If outflow boundaries or squall lines form over arid regions, a haboob may result.[15] Squall lines are depicted on NWS surface analyses as an alternating pattern of two red dots and a dash labelled SQLN or SQUALL LINE, while outflow boundaries are depicted as troughs with a label of OUTFLOW BNDRY. A haboob is a type of intense dust storm characteristic of very dry regions. ...
Tropical waves -
Atlantic tropical waves develop from disturbances which drift off the continent of Africa onto the Atlantic ocean. They are generated or enhanced by the African Easterly Jet. The clockwise circulation of the large transoceanic high-pressure cell or anticyclone centered near the Azores islands moves easterly waves away from the coastal areas of Africa towards North America. Tropical waves cause approximately 60% of Atlantic tropical cyclones and 85% of intense Atlantic hurricanes (Category 3 and greater).[16][17] Tropical waves, also known as easterly waves, are elongated areas of relatively low air pressure, oriented north to south, causing areas of cloudiness and thunderstorms. ...
Image File history File linksMetadata Size of this preview: 800 × 318 pixelsFull resolution (2374 × 944 pixel, file size: 149 KB, MIME type: image/jpeg) By NOAA, modified from http://www. ...
Image File history File linksMetadata Size of this preview: 800 × 318 pixelsFull resolution (2374 × 944 pixel, file size: 149 KB, MIME type: image/jpeg) By NOAA, modified from http://www. ...
A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ...
The African easterly jet is a region of the lower troposphere over West Africa where the seasonal mean wind speed is maximum and easterly. ...
High pressure area - Wikipedia /**/ @import /skins-1. ...
In meteorology, an anticyclone (that is, opposite to a cyclone) is a weather phenomenon in which there is a descending movement of the air and a high pressure area over the part of the planets surface affected by it. ...
Motto (Portuguese for Rather die free than in peace subjugated) Anthem (national) (local) Capital Ponta Delgada1 Angra do HeroÃsmo2 Horta3 Largest city Ponta Delgada Official languages Portuguese Government Autonomous region - President Carlos César Establishment - Settled 1439 - Autonomy 1976 Area - Total 2,333 km² (n/a) 911 sq mi...
North America North America is a continent[1] in the Earths northern hemisphere and (chiefly) western hemisphere. ...
Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ...
This article is about weather phenomena. ...
The Saffir-Simpson Hurricane Scale is a scale classifying most Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms, and thereby become hurricanes. ...
Tropical cyclones sometimes degenerate back into a tropical wave. This normally occurs if upper-level wind shear is too strong. The storm can redevelop if the upper level shear abates. If a tropical wave is moving quickly, it can have strong winds of over tropical storm force, but is not considered a tropical storm unless it has a closed circulation. An example of this was Hurricane Claudette (2003), where the original wave had winds of 45 mph before developing a circulation. Tropical waves are depicted with a solid orange line on the US National Weather Service Unified Surface Analysis.[2] Cirrus uncinus ice crystal plumes showing high level wind shear, with changes in wind speed and direction. ...
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See also Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. ...
A fictitious synoptic chart of an extratropical cyclone affecting the UK & Ireland. ...
Norwegian cyclone and Shapiro-Keyser model differences in frontal structure There are two models of cyclone development and lifecycles in common use - the Norwegian model and the Shapiro-Keyser Model. ...
A surface weather analysis for the United States on October 21, 2006. ...
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