A weather map, also known as synoptic weather chart, displays various
meteorological features across a particular area at a particular point in time and has
various symbols which all have specific meanings. Such maps have been in use since the mid-19th century and are used for research and
weather forecasting
Weather forecasting is the application of science and technology forecasting, to predict the conditions of the Earth's atmosphere, atmosphere for a given location and time. People have attempted to predict the weather informally for millennia a ...
purposes. Maps using
isotherms show temperature gradients,
which can help locate
weather fronts
A weather front is a boundary separating air masses for which several characteristics differ, such as air density, wind, temperature, and humidity. Disturbed and unstable weather due to these differences often arises along the boundary. For in ...
.
Isotach
A contour line (also isoline, isopleth, or isarithm) of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a plane section of the three-dimensional grap ...
maps, analyzing lines of equal
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
speed, on a constant pressure surface of 300 or 250
hPa HPA may refer to:
Organizations
* Harry Potter Alliance, a charity
* Halifax Port Authority, Canada
* Hamburg Port Authority, Germany
* Hawaii Preparatory Academy, a school in Hawaii, US
* Health Protection Agency, UK
* Heerespersonalamt, the Ger ...
show where the
jet stream
Jet streams are fast flowing, narrow, meandering thermal wind, air currents in the Atmosphere of Earth, atmospheres of some planets, including Earth. On Earth, the main jet streams are located near the altitude of the tropopause and are west ...
is located. Use of constant pressure charts at the 700 and 500 hPa level can indicate
tropical cyclone
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depend ...
motion. Two-dimensional
streamline
Streamline may refer to:
Business
* Streamline Air, American regional airline
* Adobe Streamline, a discontinued line tracing program made by Adobe Systems
* Streamline Cars, the company responsible for making the Burney car
Engineering
* ...
s based on wind speeds at various levels show areas of convergence and
divergence
In vector calculus, divergence is a vector operator that operates on a vector field, producing a scalar field giving the quantity of the vector field's source at each point. More technically, the divergence represents the volume density of the ...
in the wind field, which are helpful in determining the location of features within the wind pattern. A popular type of surface weather map is the
surface weather analysis
Surface weather analysis is a special type of weather map that provides a view of weather elements over a geographical area at a specified time based on information from ground-based weather stations.
Weather maps are created by plotting or tra ...
, which plots
isobars to depict areas of
high pressure
In science and engineering the study of high pressure examines its effects on materials and the design and construction of devices, such as a diamond anvil cell, which can create high pressure. By ''high pressure'' is usually meant pressures of th ...
and
low pressure
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...
. Cloud codes are translated into symbols and plotted on these maps along with other meteorological data that are included in synoptic reports sent by professionally trained observers.
History
![Francis Galton 1850s](https://upload.wikimedia.org/wikipedia/commons/e/ec/Francis_Galton_1850s.jpg)
The use of weather charts in a modern sense began in the middle portion of the 19th century in order to devise a theory on storm systems. During the
Crimean War
The Crimean War, , was fought from October 1853 to February 1856 between Russia and an ultimately victorious alliance of the Ottoman Empire, France, the United Kingdom and Piedmont-Sardinia.
Geopolitical causes of the war included the de ...
a storm devastated the French fleet at
Balaklava
Balaklava ( uk, Балаклáва, russian: Балаклáва, crh, Balıqlava, ) is a settlement on the Crimean Peninsula and part of the city of Sevastopol. It is an administrative center of Balaklava Raion that used to be part of the Cri ...
, and the French scientist
Urbain Le Verrier
Urbain Jean Joseph Le Verrier FRS (FOR) HFRSE (; 11 March 1811 – 23 September 1877) was a French astronomer and mathematician who specialized in celestial mechanics and is best known for predicting the existence and position of Neptune using ...
was able to show that if a chronological map of the storm had been issued, the path it would take could have been predicted and avoided by the fleet.
In
England
England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
, the scientist
Francis Galton
Sir Francis Galton, FRS FRAI (; 16 February 1822 – 17 January 1911), was an English Victorian era polymath: a statistician, sociologist, psychologist, anthropologist, tropical explorer, geographer, inventor, meteorologist, proto- ...
heard of this work, as well as the pioneering weather forecasts of
Robert Fitzroy
Vice-Admiral Robert FitzRoy (5 July 1805 – 30 April 1865) was an English officer of the Royal Navy and a scientist. He achieved lasting fame as the captain of during Charles Darwin's famous voyage, FitzRoy's second expedition to Tierra de ...
. After gathering information from weather stations across the country for the month of October 1861, he plotted the data on a map using his own system of symbols, thereby creating the world's first weather map. He used his map to prove that air circulated clockwise around areas of high pressure; he coined the term 'anticyclone' to describe the phenomenon. He was also instrumental in publishing the first weather map in a
newspaper
A newspaper is a periodical publication containing written information about current events and is often typed in black ink with a white or gray background.
Newspapers can cover a wide variety of fields such as politics, business, sports a ...
, for which he modified the
pantograph
A pantograph (, from their original use for copying writing) is a mechanical linkage connected in a manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen. If a line dr ...
(an instrument for copying drawings) to inscribe the map onto printing blocks. ''
The Times
''The Times'' is a British daily national newspaper based in London. It began in 1785 under the title ''The Daily Universal Register'', adopting its current name on 1 January 1788. ''The Times'' and its sister paper ''The Sunday Times'' (fou ...
'' began printing weather maps using these methods with data from the
Meteorological Office
The Meteorological Office, abbreviated as the Met Office, is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy and is led by CEO Penelope ...
.
![Wea05013 (9627284429) (cropped)](https://upload.wikimedia.org/wikipedia/commons/4/40/Wea05013_%289627284429%29_%28cropped%29.jpg)
The introduction of country-wide weather maps required the existence of national
telegraph
Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...
networks so that data from across the country could be gathered in real time and remain relevant for all analysis. The first such use of the telegraph for gathering data on the weather was the ''
Manchester Examiner
The ''Manchester Examiner'' was a newspaper based in Manchester, England, that was founded around 1845–1846. Initially intended as an organ to promote the idea of Manchester Liberalism, a decline in its later years led to a takeover by a group w ...
'' newspaper in 1847:
It was also important for time to be
standardized
Standardization or standardisation is the process of implementing and developing technical standards based on the consensus of different parties that include firms, users, interest groups, standards organizations and governments. Standardization ...
across
time zone
A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...
s so that the information on the map should accurately represent the weather at a given time. A standardized time system was first used to coordinate the British railway network in 1847, with the inauguration of
Greenwich Mean Time
Greenwich Mean Time (GMT) is the Local mean time, mean solar time at the Royal Observatory, Greenwich, Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, i ...
.
In the US, The
Smithsonian Institution
The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...
developed its network of observers over much of the central and eastern United States between the 1840s and 1860s once
Joseph Henry
Joseph Henry (December 17, 1797– May 13, 1878) was an American scientist who served as the first Secretary of the Smithsonian Institution. He was the secretary for the National Institute for the Promotion of Science, a precursor of the Smith ...
took the helm. The
U.S. Army Signal Corps
)
, colors = Orange and white
, colors_label = Corps colors
, march =
, mascot =
, equipment =
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...
inherited this network between 1870 and 1874 by an act of Congress, and expanded it to the west coast soon afterwards. At first, not all the data on the map was used due to a lack of time standardization. The United States fully adopted
time zone
A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...
s in 1905, when
Detroit
Detroit ( , ; , ) is the largest city in the U.S. state of Michigan. It is also the largest U.S. city on the United States–Canada border, and the seat of government of Wayne County. The City of Detroit had a population of 639,111 at th ...
finally established standard time.
20th century
Light tables were important to the construction of surface weather analyses into the 1990s
The use of frontal zones on weather maps began in the 1910s in
Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
. Polar front theory is attributed to
Jacob Bjerknes
Jacob Aall Bonnevie Bjerknes ( , ; 2 November 1897 – 7 July 1975) was a meteorologist. He is known for his key paper in which he pointed the dynamics of the polar front, mechanism for north-south heat transport and for which he was also awar ...
, derived from a coastal network of observation sites in
Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
during
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
. This theory proposed that the main inflow into a cyclone was concentrated along two
lines of convergence, one ahead of the low and another trailing behind the low. The convergence line ahead of the low became known as either the steering line or the warm front. The trailing convergence zone was referred to as the
squall line
A squall line, or more accurately a quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accompa ...
or cold front. Areas of clouds and
rain
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
fall appeared to be focused along these convergence zones. The concept of frontal zones led to the concept of
air mass
In meteorology, an air mass is a volume of air defined by its temperature and humidity. Air masses cover many hundreds or thousands of square miles, and adapt to the characteristics of the surface below them. They are classified according to la ...
es. The nature of the three-dimensional structure of the cyclone would wait for the development of the upper air network during the 1940s.
[University of Oklahoma]
The Norwegian Cyclone Model.
Retrieved on 2007-05-17. Since the leading edge of air mass changes bore resemblance to the
military front
In a military context, the term front can have several meanings. According to official US Department of Defense and NATO definitions, a front can be "the line of contact of two opposing forces."Leonard, B. (2011). Department of Defense Dictio ...
s of
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, the term "front" came into use to represent these lines.
The United States began to formally analyze fronts on surface analyses in late 1942, when the WBAN Analysis Center opened in downtown
Washington, D.C.
)
, image_skyline =
, image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...
In addition to surface weather maps, weather agencies began to generate constant pressure charts. In 1948, the United States began the Daily Weather Map series, which at first analyzed the 700 hPa level, which is around above
sea level
Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...
. By May 14, 1954, the 500 hPa surface was being analyzed, which is about above sea level. The effort to automate map plotting began in the United States in 1969, with the process complete in the 1970s. A similar initiative was started in India by
Indian Meteorological Department
The India Meteorological Department (IMD) is an agency of the Ministry of Earth Sciences of the Government of India. It is the principal agency responsible for meteorological observations, weather forecasting and seismology. IMD is headquarter ...
in 1969.
Hong Kong
Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China ( abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delt ...
completed their process of automated surface plotting by 1987.
By 1999, computer systems and software had finally become sophisticated enough to allow for the ability to underlay on the same workstation satellite imagery, radar imagery, and model-derived fields such as atmospheric thickness and frontogenesis in combination with surface observations to make for the best possible surface analysis. In the United States, this development was achieved when
Intergraph
Intergraph Corporation was an American software development and services company, which now forms part of Hexagon AB. It provides enterprise engineering and geospatially powered software to businesses, governments, and organizations around the w ...
workstations were replaced by n-
AWIPS
The Advanced Weather Interactive Processing System (AWIPS) is a technologically advanced processing, display, and telecommunications system that is the cornerstone of the United States National Weather Service's (NWS) operations.
AWIPS is a co ...
workstations. By 2001, the various surface analyses done within the National Weather Service were combined into the Unified Surface Analysis, which is issued every six hours and combines the analyses of four different centers.
Recent advances in both the fields of
meteorology
Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...
and
geographic information system
A geographic information system (GIS) is a type of database containing Geographic data and information, geographic data (that is, descriptions of phenomena for which location is relevant), combined with Geographic information system software, sof ...
s have made it possible to devise finely tailored products that take us from the traditional weather map into an entirely new realm. Weather information can quickly be matched to relevant geographical detail. For instance, icing conditions can be mapped onto the road network. This will likely continue to lead to changes in the way surface analyses are created and displayed over the next several years.
Plotting of data
Present weather symbols used on weather maps
Wind barb interpretation
A
station model
In meteorology, station models are symbolic illustrations showing the weather occurring at a given Weather station, reporting station. Meteorologists created the station model to fit a number of weather elements into a small space on weather maps. ...
is a symbolic illustration showing the
weather
Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...
occurring at a given
reporting station. Meteorologists created the station model to plot a number of weather elements in a small space on weather maps. Maps filled with dense station-model plots can be difficult to read, but they allow meteorologists, pilots, and mariners to see important weather patterns. A computer draws a station model for each observation location. The station model is primarily used on surface-weather maps, but can also be used to show the weather aloft. A completed station-model map allows users to analyze patterns in air pressure, temperature, wind, cloud cover, and precipitation.
Station model plots use an internationally accepted coding convention that has changed little since August 1, 1941. Elements in the plot show the key weather elements, including
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
,
dewpoint
The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will co ...
, wind, cloud cover, air pressure, pressure tendency, and precipitation.
Winds have a standard notation when plotted on weather maps. More than a century ago, winds were plotted as arrows, with feathers on just one side depicting five knots of wind, while feathers on both sides depicted of wind. The notation changed to that of half of an arrow, with half of a wind barb indicating five knots, a full barb ten knots, and a pennant flag fifty knots.
Because of the structure of the SYNOP code, a maximum of three cloud symbols can be plotted for each reporting station that appears on the weather map. All cloud types are coded and transmitted by trained observers then plotted on maps as low, middle, or high-étage using special symbols for each major cloud type. Any cloud type with significant vertical extent that can occupy more than one étage is coded as low (cumulus and cumulonimbus) or middle (nimbostratus) depending on the altitude level or étage where it normally initially forms aside from any vertical growth that takes place.
The symbol used on the map for each of these étages at a particular observation time is for the genus, species, variety, mutation, or cloud motion that is considered most important according to criteria set out by the World Meteorological Organization (WMO). If these elements for any étage at the time of observation are deemed to be of equal importance, then the type which is predominant in amount is coded by the observer and plotted on the weather map using the appropriate symbol. Special weather maps in
aviation
Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot air ...
show areas of icing and turbulence.
Types
Alaskan aviation weather map
Aviation maps
Aviation
Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot air ...
interests have their own set of weather maps. One type of map shows where VFR (visual flight rules) are in effect and where IFR (instrument flight rules) are in effect. Weather depiction plots show
ceiling height (level where at least half the sky is covered with clouds) in hundreds of feet, present weather, and cloud cover. Icing maps depict areas where icing can be a hazard for flying. Aviation-related maps also show areas of turbulence.
Constant pressure charts
left, An upper level jet streak. DIV areas are regions of divergence aloft, which usually leads to surface convergence and cyclogenesis
Constant pressure charts normally contain plotted values of temperature, humidity, wind, and the vertical height above sea level of the pressure surface. They have a variety of uses. In the mountainous terrain of the western United States and Mexican Plateau, the 850 hPa pressure surface can be a more realistic depiction of the weather pattern than a standard surface analysis. Using the 850 and 700 hPa pressure surfaces, one can determine when and where warm advection (coincident with upward vertical motion) and cold advection (coincident with downward vertical motion) is occurring within the lower portions of the
troposphere
The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
. Areas with small dewpoint depressions and are below freezing indicate the presence of icing conditions for aircraft.
The 500 hPa pressure surface can be used as a rough guide for the motion of many
tropical cyclone
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depend ...
s. Shallower tropical cyclones, which have experienced vertical
wind shear
Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizontal ...
, tend to be steered by winds at the 700 hPa level.
Use of the 300 and 200 hPa constant pressure charts can indicate the strength of systems in the lower troposphere, as stronger systems near the Earth's surface are reflected as stronger features at these levels of the atmosphere. Isotachs are drawn at these levels, which a lines of equal wind speed. They are helpful in finding maxima and minima in the wind pattern. Minima in the wind pattern aloft are favorable for
tropical cyclogenesis
Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which temperate cyclogenesis occurs. Tr ...
. Maxima in the wind pattern at various levels of the atmosphere show locations of jet streams. Areas colder than indicate a lack of significant icing, as long as there is no active
thunderstorm
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are someti ...
activity.
Surface weather analysis
Streamline analysis of the tropical Pacific Ocean
A surface weather analysis is a type of weather map that depicts positions for
high
High may refer to:
Science and technology
* Height
* High (atmospheric), a high-pressure area
* High (computability), a quality of a Turing degree, in computability theory
* High (tectonics), in geology an area where relative tectonic uplift ...
and
low-pressure area
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...
s, as well as various types of
synoptic scale
The synoptic scale in meteorology (also known as large scale or cyclonic scale) is a horizontal length scale of the order of 1000 kilometers (about 620 miles) or more. This corresponds to a horizontal scale typical of mid-latitude depressions (e. ...
systems such as
frontal zones. Isotherms can be drawn on these maps, which are lines of equal temperature. Isotherms are drawn normally as solid lines at a preferred temperature interval.
They show temperature gradients, which can be useful in finding fronts, which are on the warm side of large temperature gradients. By plotting the freezing line, isotherms can be useful in determination of precipitation type. Mesoscale boundaries such as
tropical cyclone
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depend ...
s, outflow boundaries and
squall line
A squall line, or more accurately a quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accompa ...
s also are analyzed on surface weather analyses.
Isobaric analysis is performed on these maps, which involves the construction of lines of equal mean
sea level pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The Standard atmosphere (unit), standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equival ...
. The innermost closed lines indicate the positions of relative maxima and minima in the pressure field. The minima are called low-pressure areas while the maxima are called
high-pressure area
A high-pressure area, high, or anticyclone, is an area near the surface of a planet where the atmospheric pressure is greater than the pressure in the surrounding regions. Highs are middle-scale meteorological features that result from interpl ...
s. Highs are often shown as H's whereas
lows are shown as L's. Elongated areas of low pressure, or troughs, are sometimes plotted as thick, brown dashed lines down the trough axis. Isobars are commonly used to place surface boundaries from the
horse latitudes
The horse latitudes are the latitudes about 30 degrees north and south of the Equator. They are characterized by sunny skies, calm winds, and very little precipitation. They are also known as subtropical ridges, or highs. It is a high-pressure ...
poleward, while streamline analyses are used in the tropics. A streamline analysis is a series of arrows oriented parallel to wind, showing wind motion within a certain geographic area. "C"s depict cyclonic flow or likely areas of low pressure, while "A"s depict anticyclonic flow or likely positions of high-pressure areas.
An area of confluent streamlines shows the location of
shearlines within the tropics and subtropics.
See also
*
Isobar
*
Prognostic chart
*
Surface weather analysis
Surface weather analysis is a special type of weather map that provides a view of weather elements over a geographical area at a specified time based on information from ground-based weather stations.
Weather maps are created by plotting or tra ...
References
{{Authority control
Map types
Synoptic meteorology and weather
Weather prediction
British inventions