A station model is a symbolic illustration showing the weather occurring at a given reporting station. The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time. A weather station is a facility with instruments and equipment to make observations of atmospheric conditions in order to provide information to make weather forecasts Meteorologists created the station model to plot a number of weather elements in a small space on weather maps. A weather map is a tool used to display information quickly showing the analysis of various meteorological quantities at various levels of the atmosphere 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. ^[1]

Station model plots use an internationally-accepted coding convention that has changed little since August 1, 1941. Events 30 BC - Octavian (later known as Augustus enters Alexandria, Egypt, bringing it under the control of the Roman Year 1941 ( MCMXLI) was a Common year starting on Wednesday (the link will display 1941 calendar of the Gregorian calendar. Elements in the plot show the key weather elements, including temperature, dewpoint, wind, cloud cover, air pressure, pressure tendency, and precipitation. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The dew point (sometimes spelled dewpoint) is the Temperature to which a given parcel of Air must be cooled at constant Barometric pressure, ^{[2] [3]}

Contents 1 Measurement location and units 2 Plotted winds 3 Cloud cover 4 Cloud types 5 Present weather and visibility 6 Temperature and dewpoint 7 Sea level pressure and height of pressure surface 8 Pressure tendency 9 Past weather 10 See also 11 References

Measurement location and units

Weather maps primarily use the station model to show surface weather conditions, but the model can also show the weather aloft as reported by a weather balloon's radiosonde or a pilot's report. A radiosonde ( Sonde is French for Probe) is a unit for use in Weather balloons that measures various atmospheric parameters A pilot report or PIREP is a report of actual Weather conditions encountered by an Aircraft in flight

Station model plots use a mixture of metric and Imperial units depending on the map's location and what is being shown. Imperial units or the Imperial system is a collection of units first defined in the British Weights and Measures Act of 1824 Surface maps in the United States primarily use Imperial units, such inches, degrees Fahrenheit, and knots. Imperial units or the Imperial system is a collection of units first defined in the British Weights and Measures Act of 1824 Inches redirects here To see the Les Savy Fav album see Inches. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 Most of the world, however, uses metric measurements for everything but wind speed, which is shown in knots.

Plotted winds

Further information: Wind barb

The station model uses a wind barb to show both wind direction and speed. Wind Barbs are symbols used on Weather maps[[http //polarncep Wind Barbs are symbols used on Weather maps[[http //polarncep The wind barb shows the speed using "flags" on the end.

• Each half of a flag depicts five knots
• Each full flag depicts 10 knots
• Each pennant (filled triangle) depicts 50 knots^[4]

Winds are depicted as blowing from the direction the flags are facing. The Commissioning pennant or Masthead pennant is a Pennant (also spelt "pendant" flown from the Masthead of a Warship. Therefore, a northeast wind will be depicted with a line extending from the cloud circle to the northeast, with flags indicating wind speed on the northeast end of this line. ^[5] Once plotted on a map, an analysis of isotachs (lines of equal wind speeds) can be accomplished. A contour line (also Level set, isopleth, isoline, isogram or isarithm) of a function of two Isotachs are particularly useful in diagnosing the location of the jet stream on upper level constant pressure charts, usually at or above the 300 hPa level. ^[6]

More than a century ago, winds were initially plotted as arrows facing downwind, with feathers on both sides of the staff to indicate wind direction. ^[7] In the United States, the change to the modern convention of flags shown on one side of the staff to indicate wind speed took effect on August 1, 1941. The United States of America —commonly referred to as the Events 30 BC - Octavian (later known as Augustus enters Alexandria, Egypt, bringing it under the control of the Roman Year 1941 ( MCMXLI) was a Common year starting on Wednesday (the link will display 1941 calendar of the Gregorian calendar. ^[8][9]

Cloud cover

See also: Cloud cover

Along with wind direction, cloud cover is one of the oldest atmospheric conditions to be coded on a station model. Cloud cover (also known as cloudiness, cloudage or cloud amount) refers to the fraction of the Sky obscured by Clouds when observed ^[7][10] The circle in the middle of the station model represents cloud cover. In the United Kingdom, when the observation is taken from an automated weather observation site, the shape is a triangle. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located ^[11] If the shape is completely filled in, it is overcast. If conditions are completely clear, the circle or triangle is empty. If conditions are partly cloudy, the circle or triangle is partially filled in. ^[3] The cloud cover shape has different looks depending upon how many oktas (eighths of the sky) and covered by cloud. OKTA is the only Oil refinery in the Republic of Macedonia. It is situated outside the capital city of Skopje. A sky half full of clouds would have a circle that was half white and half black. Below the shape indicating sky cover, the station model can indicate the coverage of low clouds, in oktas, and the ceiling height in hundreds of feet. The ceiling height is the height at which more than half the sky is covered by clouds.

For pilots, knowledge of the sky cover helps determine if visual flight rules are being met. Knowing the degree of cloud cover can help determine whether or not various weather fronts, such as cold fronts or warm fronts, have passed by a location. A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena. A cold front defined as the leading edge of a cooler and drier mass of air A warm front is defined as the leading edge of an advancing mass of warm air it separates warm air from the colder air ahead A nephanalysis, contouring areas that are cloudy with scalloped lines, can be performed to indicate a system's cloud and precipitation pattern. A nephanalaysis is the analysis of a synoptic chart focusing on the types and amount of clouds and precipitation ^[12] This technique is rarely performed nowadays, due to the prevalence of satellite imagery worldwide. ^[13]

Cloud types

See also: Clouds

Above or below the shape indicating sky cover can lie a symbol indicating cloud type. A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another Planetary body One cloud type is depicted for each of three possible cloud layers, if known. The top two cloud layer types are depicted above the sky cover circle in the station model, while the lowest cloud type is indicated below the sky cover circle. ^[5] The symbols used for clouds emulate the cloud shape. Cirrus is indicated by a couple hooks, cumulus are indicated by a mound shape, with cumulonimbus indicated with an upside down trapezoid on top of the cumulus symbol to indicate its anvil. Cumulonimbus (Cb is a type of Cloud that is tall dense and involved in Thunderstorms and other intense Weather. Since the station model has limited room, when there is more than one cloud type present per level, the cloud type with the highest priority is included. ^[14] Knowing the cloud type at various locations can help determine whether or not a weather front has passed by a particular location. A low deck of stratus could indicate a station is still north of a warm front, while thunderstorms can indicate the approach of a squall line or cold front. A squall line is a line of severe thunderstorms that can form along and/or ahead of a Cold front.

Low cloud types

Mid cloud types

High cloud types

Present weather and visibility

To the left of the cloud shape in the center of the station model is the symbol depicting present weather. The present weather symbol depicts the current weather which normally is obstructing the visibility at the time of observation. In Meteorology, visibility is a measure of the Distance at which an object or light can be clearly discerned The visibility itself is shown as a number, in statute miles in the United States and meters elsewhere, describing how far the observer can see at that time. A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International This number is located to the left of the present weather symbol. ^[5] For pilots, knowledge of the horizontal visibility helps determine if instrument flight rules are being met during foggy or smokey conditions, as well as during periods of intense precipitation. Present weather depicted with the station model can include:

• Dust
• Fog
• Haze
• Ocean spray
• Precipitation
• Sand
• Smoke
• Thunderstorms
• Volcanic ash

Temperature and dewpoint

To left of center in the station model, the temperature and dewpoint are plotted. Dust is a general name for minute Solid particles with Diameters less than 500 micrometers. Fog is a cloud that is in contact with the ground Stratus clouds are usually the only clouds that touch the ground Haze is traditionally an atmospheric phenomenon where dust smoke and other dry particles obscure the clarity of the sky In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles Smoke is the collection of airborne solid and liquid Particulates and Gases ref> ''Smoke Production and Properties'' - SFPE Handbook of Fire Protection Engineering Volcanic ash consists of small Tephra, which are bits of pulverized rock and glass created by volcanic eruptions less than in diameter Within the United States on surface weather maps, they are still plotted in degrees Fahrenheit. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 ^[5] Otherwise, they will be in units of degrees Celsius. The Celsius Temperature scale was previously known as the centigrade scale. This knowledge is important to meteorologists because when this data is plotted on a map, isotherms and isodrosotherms (lines of equal dewpoint) are easily analyzed, either by man or machine, which can help determine location of weather fronts. A contour line (also Level set, isopleth, isoline, isogram or isarithm) of a function of two A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena.

Sea level pressure and height of pressure surface

See also: Sea level pressure

On the top right corner of the model for a surface weather map is the pressure, showing the last two integer digits of the pressure in millibars, or hectopascals, along with the first decimal. The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. For instance, if the pressure at a certain location is 999. 7 hPa, the pressure portion of the station model will read 997. Although the first digit or two of the pressure is left off, other nearby stations give away whether or not the first digits is a 10 or a 9. Most of the time, choosing first digits that would lead to a value nearest to 1000 works out best. ^[5] The plotting of this value within the station model allows for the analysis of isobars on weather maps. Within maps which plot data on constant pressure surfaces, the pressure is replaced with the height of the pressure surface. ^[15]

Pressure tendency

See also: Atmospheric tides and Atmospheric pressure

Below the pressure will lie the pressure tendency figure, which indicates the pressure change over the past three hours. Atmospheric tides are global-scale periodic oscillations of the Atmosphere. The number depicting the pressure change will usually have two digits and indicate the pressure change in 0. 1 millibar increments. There are nine different figures which represent the pressure change. A slant angled up and right indicates a steady rise, while a downward slant to the lower right indicates a steady fall. Steady rises can indicate improving conditions and approaching high pressure, and normally occur in the wake of a cold front. Steady falls can indicate deteriorating conditions and an approaching low pressure area, with the largest falls occurring in advance of a surface cyclone and its attendant warm front. In Meteorology, a cyclone refers to an area of closed circular fluid motion rotating in the same direction as the Earth. A warm front is defined as the leading edge of an advancing mass of warm air it separates warm air from the colder air ahead ^[16]

The time of the day must be considered, as there are two natural rises per day (locally around 10 am and 10 pm) and two natural falls per day (locally around 4 am and 4 pm). These daily changes in pressure can mask the movement of pressure systems and fronts past a location. The lowest natural dip in the pressure, in a stagnant weather pattern, occurs around 4 pm while the highest natural peak in pressure occurs around 10 am. ^[17] Once plotted on a map, the analysis of isallobars (lines of equal pressure change) can be plotted on a map, which can indicate the direction of motion of high and low pressures systems across the map domain. ^[18]

Past weather

Station models can have past weather plotted within them, which would be located just under the pressure tendency. They indicate the type of weather experienced during the past six hours. The weather types are limited to obstructions of visibility and precipitation. ^[5]

See also

• Surface weather analysis
• Weather map

References

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