Often, when we leave home for several hours, we do not know how the weather will change. Remember the times when you were caught in the rain without an umbrella and looked for shelter or wore clothes that were too warm and felt uncomfortable. Even modern gadgets do not always provide us with the opportunity to quickly find out the weather, but by observing the direction of the wind, cloudiness, sky color, and other signs, we can learn to predict the weather for the near future.
Weather is the state of the atmosphere in a given area, in given time. The main elements of weather are Atmosphere pressure, temperature and humidity. The main weather phenomena are wind, clouds, precipitation.
At the same temperature, but different air humidity, with or without precipitation, with or without wind, the weather will be perceived differently by a person. For example, cool weather with wind is often more difficult for people to tolerate than colder weather without wind. Weather cannot be characterized by a single element or phenomenon, since it is a combination of them. The concept of weather refers to the current state of the atmosphere, so it experiences continuous changes.
The weather is characterized by variability, which is periodic in nature (daily and seasonal weather changes) and non-periodic in nature (changes associated with the circulation of air masses). Since weather changes are associated with fronts, cyclones and anticyclones, classes are distinguished: warm front weather, cold front weather, cyclonic weather, anticyclonic weather.
Local signs of a warm front.
The passage of a warm front is usually accompanied by thick nimbostratus clouds with continuous rain. The first messenger of a warm front is cirrus clouds, gradually turning into continuous cirrostratus. The pressure drops. The closer to the atmospheric front line, the denser the clouds become. Then the clouds become lower, the wind intensifies and changes its direction. Light rain or snow begins. When the warm front has passed, the rain or snow has stopped, the clouds dissipate, warming sets in - a warmer air mass has arrived.
Clouds characteristic of the passage of a warm front.
Local signs of a cold front.
If warm air retreats and cold air dissipates after it, it means a cold front is approaching. Warm air is quickly forced upward and powerful piles of cumulus and cumulonimbus clouds are created. The clouds of the cold front carry showers, thunderstorms, accompanied by strong gusty winds. Since the cold front usually moves quickly, stormy weather does not last long - from 15-20 minutes to 2-3 hours. As a result of the interaction of cold air with the warm underlying surface, individual cumulus clouds with gaps are formed. Then comes clarity.
Local signs of unstable weather of a cyclonic nature.
If the tops of especially high clouds cease to appear sharply in the sky, as if covered with a veil, then from such a cloud in the fall you can soon expect a downpour or a thunderstorm. If powerful and high cumulus clouds appear during the day, if there was a thunderstorm, but after it it did not get colder, expect another thunderstorm at night. Before a night thunderstorm, fog does not appear in the evening, and dew does not fall. If the sky is cloudy and whitish during the day, the evening dawn is red, and the Sun is covered by a cloud, because of which only its diverging rays are visible, it will rain. The wind is uneven throughout the day: it weakens and then increases sharply. If it intensifies into the night, it further increases the likelihood of unsettled weather. In late autumn, during frosts (but before snow falls) and in early spring after the snow has melted, after sunny day, instead of dew, everything is covered with silvery frost.
Local signs of continued good anticyclonic weather.
Signs that foretell better weather are based on the fact that prolonged bad weather always comes with cyclones. Therefore, improved weather is possible when the cyclone passes. The main sign of improving weather is the erosion of uniform low continuous gray clouds, which is observed during prolonged bad weather. The amount of clouds gradually and evenly decreases. Gaps and gaps form in stratus clouds. Cumulus clouds appear and move in the same direction as the wind near the ground.
Cooling during bad weather is a sure sign of an imminent cessation of precipitation. The stronger the cold snap, the more reliable the sign. It is much warmer in the forest than in the field.
Signs of thunderstorms and showers in hot weather.
During the day it is very warm or hot, the humidity is high, stuffy, steamy. As a thunderstorm approaches, the wind begins to blow towards the thundercloud and then changes its direction by 180°. Cumulus clouds grow upward and pile up during the day. Then the top of the thundercloud begins to spread out to the sides. How greater height the top of a thundercloud reaches, the larger and heavier the rain, the more likely it is to hail.
Signs of a possible overnight thunderstorm.
Before a night thunderstorm, the air temperature in the evening almost does not drop; the evening and night are warm and stuffy. In the evening, fog and dew do not appear or quickly disappear. By evening the clouds remain, partially turning into stratocumulus.
Signs of weather change
Worsening weather
The approach of a warm front, i.e. inclement weather and fresh wind after 6-12 hours:
1. Atmospheric pressure gradually decreases.
2. Cirrus claw-shaped clouds quickly moving from the horizon appear, which are gradually replaced by cirrostratus clouds, turning into a denser layer of altostratus clouds.
3. Cirrus and cirrostratus clouds move to the right of the surface wind melting.
4. Increased visibility, increased refraction - the appearance of objects from behind the horizon, mirages; increased audibility of sounds in the air.
5. Smoke from the chimney spreads below.
6. The appearance of small halos and crowns in the corresponding cloud layers; strong twinkling of stars at night.
7. The morning dawn is bright red.
8. In summer there is no dew at night and in the morning.
9. In the evening the Sun sets into the thickening clouds.
Approaching cold front, thunderstorm and storm 1-2 hours before it starts:
1. A sharp drop in atmospheric pressure.
2. The appearance of cirrocumulus, altocumulus tower and lenticular clouds;
3. Wind instability.
4. The appearance of strong interference in radio reception.
5. Clouds are observed in the form of an elongated strip.
6. The appearance of characteristic noise in open water from the approaching thunderstorm or squall. There are no more than 10 minutes left before the squall.
7. Abrupt development of cumulonimbus clouds.
Better weather
After the passage of a warm front or an occlusion front, i.e. merging of warm and cold fronts, you can expect a cessation of precipitation and weakening winds in the next 4 hours if:
1. The pressure drop stops, the pressure trend becomes positive.
2. The height of the clouds increases, gaps appear in the clouds, nimbostratus clouds turn into stratocumulus and stratus.
3. The wind turns to the right and weakens.
4. Absolute and relative humidity tend to decrease.
5. The excitement begins to calm down.
6. In some places, fog forms over the body of water (at water temperatures below air temperatures).
After the passage of a cold front of the second kind, you can expect a cessation of precipitation, a change in wind direction and clearing in 2-4 hours if there is:
1. A sharp increase in atmospheric pressure.
2. A sharp turn of the wind to the right.
3. A sharp change in the nature of cloudiness, an increase in clearances.
4. A sharp increase in visibility.
5. Lowering the temperature.
Preservation of weather patterns for the near future
General signs:
1. Repetition of meteorological elements of the past day in terms of observations.
2. Type of cloud cover, visibility, type of precipitation, color of the sky, color of dawn, audibility of radio reception, sea state, type and nature of waves, optical phenomena in the atmosphere are similar to those of the past day.
3. If the direction of movement of clouds located at different heights remains almost unchanged, then in the next 6-12 hours we can expect weather without precipitation, with moderate winds.
Good anticyclonic weather with calm winds or calm, clear skies or light clouds and good visibility will persist over the next 12 hours if:
1. High atmospheric pressure does not change or increases.
2. Regularly changing breezes are observed in the coastal strip.
3. Individual cirrus clouds that appear in the morning disappear by midday.
4. In the morning and evening, smoke from the chimney rises vertically (at low speed).
5. At night and by morning there is dew on the deck, spar and other objects.
6. The disk of the Sun is deformed at sunrise and sunset.
7. Golden and pink shades of dawn and a silvery glow in the sky are observed.
8. There is a dry haze near the horizon.
9. The sun drops below the clear horizon.
10. Green color is observed when stars twinkle.
Bad weather - cloudy, with precipitation, strong wind, poor visibility will continue for the next six hours or more:
1.Low or decreasing atmospheric pressure.
2. Absolute and relative humidity are elevated and change little during the day.
3. The nature of cloudiness (nimbostratus, cumulonimbus clouds) does not change.
4. The air temperature is lower in summer and higher in winter.
5. The wind is fresh, does not change strength, character and almost does not change direction.
6. If thunder rumbles in summer in cold, rainy weather, then we must expect prolonged cool weather.
The weather for tomorrow will improve:
1. If cumulus clouds appear in the morning and disappear by evening.
2. If in the evening after bad weather the sun comes out and there are no clouds in the western part of the sky.
3. If the night is quiet and cool, and the moon is setting in a clear sky.
4. Marigolds unfolded their corollas in the morning - to clear weather.
5. Sparrows fly in flocks - for dry and clear weather.
6. Midges “pushing the poppy” - for good weather.
7. The evening forest is warmer than the field - good weather.
8. Beetles fly in the evening - good weather.
10. In the evening grasshoppers chirp loudly - there will be good weather.
11. The nightingale sings incessantly all night - before the warm day.
12. If the fog falls down and falls on the ground, the weather will be good.
13. Fog that disappears after sunrise also promises good weather.
14. If smoke rises upward, even during bad weather, but without wind, this means good weather.
15. If the rainbow is located in the east and in the afternoon, the weather will improve.
16. Heavy dew in the morning - good weather.
Name at least two signs of a warm atmospheric front
Heavy dew means a clear day.
18. Cumulus clouds move in the same direction as the wind near the ground - towards clear weather.
19. If the sunset is clear, it will be clear.
20. If the Milky Way is full of stars and bright - good weather.
21. Cumulus clouds do not develop in height in the afternoon - a sign of the cessation of rain.
22. If, during inclement weather, individual cumulus clouds move quickly across the sky in the same direction in which the wind blows at the surface of the sea, the weather will soon improve, precipitation will stop, and the wind will weaken.
The weather for tomorrow will worsen:
1. If the wind does not subside in the evening, but intensifies.
2. If cumulus clouds appear in the morning, which by midday will take the form of tall towers or mountains.
3. If clouds of all types are visible in the sky at the same time: cumulus, “lamb”, cirrus and wavy.
4. If smoke spreads along the ground.
5. If on a cloudy day the sun shines brightly before sunset.
6. The river will rustle, the frog will scream - it means rain.
7. The sky “sweeps away”, becomes cloudy - it means rain.
8. If the grass is dry in the morning, you should expect rain by nightfall.
9. If sparrows bathe in dust, it means rain.
10. Burdock cones straighten the hooks - before the rain.
11. Flowers smell strong before the rain.
12. Swallows fly up and down - before a storm (check the mooring lines).
13. If there is fog over the forest, it will rain.
14. Smoke without wind clings to the ground: in summer - to rain, in winter - to snow.
15. If in the summer at sunset the clouds thicken, darken and become lead-colored, there will be a thunderstorm at night.
16. Cirrus clouds promise bad weather for two days or more.
17. If the clouds move towards each other, expect bad weather.
18. After a lot of thunder, there’s a lot of rain.
19. In the morning you can hear thunder - in the evening there is rain and wind.
20. The sun sets in the fog - expect rain.
21. Red evening dawn - to the wind, pale - to the rain.
22. Increasing wind towards the end of the day or night with a simultaneous increase in cloudiness means worsening weather.
23. If the sun at sunrise seems a little larger than usual, you need to wait for rain.
24. When two layers of clouds move quickly across or towards each other, this is a sure sign of an imminent sharp deterioration in the weather (precipitation, strong gusty winds).
25. If the leaves of the trees are turned inward, then expect rain.
26. The rapid movement of clouds, opposite to the direction of the wind at the surface, indicates the approach of inclement weather with thunderstorms and strong winds.
27. At sunset, stripes of cirrus clouds are visible in the west, which seem to emerge from one point - to worsening weather.
28. The bright red morning dawn rises high in the sky - to precipitation, the crimson-red evening dawn - to the wind.
Stars
1. If the stars are very frequent in winter - it means cold, in summer - it means clear weather.
2. In summer, few stars are visible in the sky - this means bad weather.
3. When the stars twinkle strongly at night, and clouds in the morning, there will be a thunderstorm at noon.
4. White and red circles around the stars mean good weather, black circles mean rain.
5. If the Milky Way is full of stars and bright, it means good weather, if it’s dim, it means bad weather.
6. Stars fall - towards the wind.
7. And if the stars “play” (shimmer, change brightness) in the summer, it means rain and wind.
Moon
1. A clear round moon in summer means good weather, in winter it means cold weather.
2. The month is red - for rain.
3. A ring around the moon - towards the wind.
4. If the moon is pale or cloudy, then there will be rain, but if it is clear, the weather will be good.
Common signs of weather change
Swifts and swallows fly low - they foretell rain; high - good weather.
The bindweed flowers are closing - rain is coming; bloom in cloudy weather - on sunny days.
Fog spreads across the water in the morning - to good weather, rises - to rain.
When a rainbow appears in the morning, there will be rain, and if in the evening, good weather is possible (especially if the rainbow appears in the eastern part of the horizon).
The greener the rainbow, the more rain there will be.
If there is more red in the rainbow, then the weather will clear up, and if it is blue, the bad weather will drag on.
Thunder in early spring - before the cold.
If thunder booms continuously, there will be hail.
If the sun turns red on the north side during sunset in summer, there will be frost or cold dew.
The sun at sunset and the slope of the sky are red - before the wind.
Jerky, short thunder means good weather, long and rolling thunder means bad weather.
Before it rains, the water in the river turns dark.
If animals and birds are quieter than usual, get ready for bad weather.
If you stand with your back to the wind open area, then worsening weather should be expected only on the left.
If the movement of clouds is deviated in the northern hemisphere by left side relative to the direction of the wind at the surface of the water, good weather should be expected. If the clouds deviate noticeably in right side This means that the front part of the cyclone is passing through this area, and we should expect a significant deterioration in the weather.
If the direction of movement of low clouds slowly turns against the sun, it means that the wind will subside and warm weather will be replaced by colder, stormy weather. If the clouds turn in the direction of the sun, then the opposite is true.
Atmospheric front. Warm and cold front
Helpful information:
Weather can be defined as a certain state of the atmosphere in a particular area at any time. Weather is variable both for a specific area and throughout the Earth.
Weather consists of a number of characteristics. These are air temperature, humidity, precipitation, atmospheric pressure, cloudiness, wind direction and speed. Other characteristics are also used to make special weather forecasts.
The main reason why the weather changes is air temperature. When the temperature changes, other weather characteristics also change. Temperature affects air humidity and atmospheric pressure.
Warm front
As it increases, humidity increases and atmospheric pressure decreases.
Following the increase in air humidity, cloudiness increases. Changes in atmospheric pressure, in turn, lead to the emergence of winds.
The wind moves layers of air that may differ from those in a given area. Therefore, in addition to temperature, wind can also be a primary factor for weather change.
Any region of the troposphere with homogeneous properties is called air mass. The wind moves air masses and brings new weather conditions to the territory. If the air mass was warmer than the one located above the territory, then the air temperature here will rise, the pressure will decrease, and precipitation may fall.
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WEATHER - the state of the atmosphere in a certain place at a certain time or period of time (year, month, day). IN environment there is nothing more changeable than the weather: today people are sweltering from the heat; tomorrow they will get wet in the rain; the wind suddenly blows up, sometimes reaching the strength of a hurricane, and then it subsides, becomes warmer, and an amazing peace is established in nature. But the weather also obeys strict laws. It is not always possible to catch them right away, because too many different factors influence the formation of weather.
Weather is characterized by certain meteorological elements. These are atmospheric pressure, solar radiation, temperature, air humidity, wind strength and direction, precipitation, cloudiness. Each weather has its own set of symptoms. They are usually closely related to each other. For example, if air pressure decreases in summer, it is usually followed by a decrease in temperature, an increase in humidity, the wind increases, and it begins to rain.
Weather changes can occur every minute or daily, however, a pattern is observed here: weather changes are periodic, that is, repeated over a period of time, in nature.
5. Features of weather conditions of atmospheric fronts.
These are changes in weather characteristics throughout the year associated with the change of seasons, and changes during the day due to the change of day and night. The greatest weather variability is observed in temperate latitudes, especially in areas with continental climate. At equatorial and polar latitudes, seasonal or daily weather changes are weak or practically absent. This is explained by the low variability of radiation conditions at these latitudes.
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Weather. Signs of the weather. Air masses. Atmospheric fronts. Cyclones and anticyclones.
Weather call the state of the lower layer of the atmosphere at a given time and place.
Its most characteristic feature is variability; often the weather changes several times during the day.
Sudden changes in weather are most often associated with changes in air masses.
Air mass – this is a huge moving volume of air with certain physical properties: temperature, density, humidity, transparency.
The lower layers of the atmosphere, in contact with the underlying surface, acquire some of its properties. Warm air masses form above a heated surface, and cold air masses form above a cooled surface. The longer the air mass remains above the surface from which moisture evaporates, the greater its humidity becomes.
Depending on the place of formation, air masses are divided into arctic, temperate, tropical, and equatorial. If the formation of air masses occurs over the ocean, they are called marine. In winter they are very humid and warm, in summer they are cool. Continental air masses have low relative humidity, more high temperatures and are very dusty.
Russia is located in the temperate zone, so maritime temperate air masses predominate in the west, and continental air masses predominate over most of the rest of the territory. Arctic air masses form beyond the Arctic Circle.
When different air masses come into contact in the troposphere, transition regions arise - atmospheric fronts, their length reaches 1000 km, and their height reaches several hundred meters.
Warm front is formed when warm air actively moves towards cold air. Then light warm air flows onto the retreating wedge of cold air and rises along the interface plane. It cools as it rises. This leads to condensation of water vapor and the formation of cirrus and nimbostratus clouds, and then to precipitation.
When a warm front approaches within a day, its harbingers appear - cirrus clouds. They float like feathers at an altitude of 7-10 km. At this time, atmospheric pressure decreases. The arrival of a warm front is usually associated with warming and heavy, drizzling precipitation.
Cold front formed when cold air moves towards warm air. Cold air, being heavier, flows under the warm air and pushes it upward. In this case, stratocumulus rain clouds appear, piling up like mountains or towers, and precipitation from them falls in the form of showers with squalls and thunderstorms. The passage of a cold front is associated with colder temperatures and stronger winds.
Powerful turbulences of air sometimes form at fronts, similar to whirlpools when two streams of water meet. The size of these air vortices can reach 2–3 thousand km in diameter. If the pressure in their central parts is lower than at the edges, this is cyclone.
In the central part of the cyclone, the air rises and spreads to its outskirts. As it rises, the air expands, cools, water vapor condenses and clouds appear. When cyclones pass, cloudy weather usually occurs with rain in summer and snowfall in winter. Cyclones usually move from west to east from average speed about 30 km/h, or 700 km per day.
Tropical cyclones differ from temperate cyclones by being smaller in size and having exceptionally stormy weather. The diameter of tropical cyclones is usually 200–500 km, the pressure in the center drops to 960–970 hPa. They are accompanied hurricane winds up to 50 m/s, and the width of the storm zone reaches 200–250 km. In tropical cyclones, powerful clouds form and heavy precipitation falls (up to 300–400 mm per day). Feature tropical cyclones - the presence in the center of a small, with a diameter of about 20 km, calm area with clear weather.
If, on the contrary, the pressure is increased in the center, then this vortex is called anticyclone. In anticyclones, the outflow of air at the Earth's surface occurs from the center to the edges, moving clockwise. Simultaneously with the outflow of air from the anticyclone into its central part air comes from upper layers atmosphere. As it descends, it heats up, absorbing water vapor, and the clouds dissipate. Therefore, in areas where anticyclones appear, clear, cloudless weather with weak winds sets in, hot in summer and cold in winter.
Anticyclones cover larger areas than cyclones. They are more stable, move at a lower speed, break down more slowly, and often stay in one place for a long time. As the anticyclone approaches, the atmospheric pressure increases. This sign should be used when predicting the weather.
A series of cyclones and anticyclones continuously pass through the territory of Russia. This is what causes weather variability.
Synoptic map- a weather map compiled for a specific period. It is compiled several times a day based on data received from the network weather stations Hydrometeorological Service of Russia and foreign countries. This map shows weather information in numbers and symbols - air pressure in millibars, air temperature, wind direction and speed, cloudiness, position of warm and cold fronts, cyclones and anticyclones, precipitation patterns.
To forecast the weather, maps are compared (for example, for November 3 and 4) and changes in the position of warm and cold fronts, the displacement of cyclones and anticyclones, and the nature of the weather in each of them are established. Currently, space stations are widely used to improve weather forecasts.
Signs of stable and clear weather
1. Air pressure is high, hardly changes or increases slowly.
2. Sharply expressed diurnal cycle temperatures: hot during the day, cool at night.
3. The wind is weak, intensifies in the afternoon, and subsides in the evening.
4. The sky is cloudless all day or covered with cumulus clouds, disappearing in the evening. Relative humidity air decreases during the day and increases towards night.
5. During the day the sky is bright blue, twilight is short, the stars twinkle faintly. In the evening the dawn is yellow or orange.
6. Heavy dew or frost at night.
7. Fogs over lowlands, increasing at night and disappearing during the day.
8. At night it is warmer in the forest than in the field.
9. Smoke rises from chimneys and fires.
10. Swallows fly high.
Signs of Unsustainable Severe Weather
1. The pressure fluctuates sharply or continuously decreases.
What is an atmospheric front
The daily variation of temperature is weakly expressed or with a violation of the general variation (for example, at night the temperature rises).
3. The wind increases, abruptly changes its direction, the movement of the lower layers of clouds does not coincide with the movement of the upper ones.
4. Cloudiness is increasing. Cirrostratus clouds appear on the western or southwestern side of the horizon and spread throughout the sky. They give way to altostratus and nimbostratus clouds.
5. It’s stuffy in the morning. Cumulus clouds grow upward, turning into cumulonimbus - to a thunderstorm.
6. Morning and evening dawns are red.
7. By night the wind does not subside, but intensifies.
8. Light circles (halos) appear around the Sun and Moon in cirrostratus clouds. There are crowns in the middle-tier clouds.
9. There is no morning dew.
10. Swallows fly low. Ants hide in anthills.
A warm front is marked in red or with blackened semicircles directed in the direction of the front's movement. As the warm front line approaches, pressure begins to drop, clouds thicken, and heavy precipitation begins to fall. In winter, low stratus clouds usually appear when a front passes. The temperature and humidity are slowly increasing. As a front passes, temperatures and humidity typically rise quickly and winds pick up. After the front passes, the wind direction changes (the wind turns clockwise), the pressure drop stops and its slight increase begins, the clouds dissipate, and precipitation stops. The field of pressure trends is presented as follows: in front of the warm front there is a closed area of pressure drop, behind the front there is either an increase in pressure or a relative increase (a decrease, but less than in front of the front).
In the case of a warm front, warm air, moving towards the cold air, flows onto a wedge of cold air and glides upward along this wedge and is dynamically cooled. At a certain height, determined by the initial state of the rising air, saturation is achieved - this is the level of condensation. Above this level, cloud formation occurs in the rising air. Adiabatic cooling of warm air sliding along a wedge of cold air is enhanced by the development of upward movements from unsteadiness with a dynamic drop in pressure and from the convergence of wind in the lower layer of the atmosphere. Cooling of warm air during upward sliding along the surface of the front leads to the formation of a characteristic system of stratus clouds (upward sliding clouds): cirrostratus - altostratus - nimbostratus (Cs-As-Ns).
When approaching a point of a warm front with well-developed cloudiness, cirrus clouds first appear in the form of parallel stripes with claw-shaped formations in the front part (harbingers of a warm front), elongated in the direction of air currents at their level (Ci uncinus). The first cirrus clouds are observed at a distance of many hundreds of kilometers from the front line near the Earth's surface (about 800-900 km). Cirrus clouds then become cirrostratus clouds. These clouds are characterized by halo phenomena. The upper tier clouds - cirrostratus and cirrus (Ci and Cs) consist of ice crystals and do not produce precipitation. Most often, Ci-Cs clouds represent an independent layer, the upper boundary of which coincides with the axis of the jet stream, that is, close to the tropopause.
Then the clouds become more and more dense: altostratus clouds (Altostratus) gradually turn into nimbostratus clouds (Nimbostratus), blanket precipitation begins to fall, which weakens or stops completely after passing the front line. As you approach the front line, the height of the base Ns decreases. Its minimum value is determined by the height of the condensation level in the rising warm air. Altolayers (As) are colloidal and consist of a mixture of tiny droplets and snowflakes. Their vertical thickness is quite significant: starting at an altitude of 3-5 km, these clouds extend to altitudes of the order of 4-6 km, that is, they are 1-3 km thick. Precipitation falling from these clouds in the summer, passing through the warm part of the atmosphere, evaporates and does not always reach the Earth's surface. In winter, precipitation from As as snow almost always reaches the Earth's surface and also stimulates precipitation from the underlying St-Sc. In this case, the width of the zone of continuous precipitation can reach a width of 400 km or more. Closest to the Earth's surface (at an altitude of several hundred meters, and sometimes 100-150 m and even lower) is the lower boundary of nimbostratus clouds (Ns), from which precipitation falls in the form of rain or snow; Nimbostratus clouds often develop under nimbostratus clouds (St fr).
Ns clouds extend to heights of 3...7 km, that is, they have a very significant vertical thickness. Clouds also consist of ice elements and droplets, and the droplets and crystals, especially in the lower part of the clouds, are larger than in As. The lower base of the As-Ns cloud system in general outline coincides with the front surface. Since the top of As-Ns clouds is approximately horizontal, their greatest thickness is observed near the front line. At the center of the cyclone, where the cloud system of the warm front is most developed, the width of the cloud zone Ns and the zone of heavy precipitation is on average about 300 km. In general, As-Ns clouds have a width of 500-600 km, the width of the Ci-Cs cloud zone is about 200-300 km. If we project this system onto a ground map, then all of it will appear in front of the warm front line at a distance of 700-900 km. In some cases, the zone of cloudiness and precipitation can be much wider or narrower, depending on the angle of inclination of the frontal surface, the height of the condensation level, and the thermal conditions of the lower troposphere.
At night, radiative cooling of the upper boundary of the As-Ns cloud system and a decrease in temperature in the clouds, as well as increased vertical mixing as cooled air descends into the cloud, contributes to the formation of an ice phase in the clouds, the growth of cloud elements and the formation of precipitation. As you move away from the center of the cyclone, the upward air movements weaken and precipitation stops. Frontal clouds can form not only over the inclined surface of the front, but in some cases, on both sides of the front. This is especially typical for the initial stage of a cyclone, when upward movements capture the frontal region - then precipitation can fall on both sides of the front. But behind the front line, frontal clouds are usually highly stratified and post-frontal precipitation is often in the form of drizzle or snow grains.
In the case of a very flat front, the cloud system may be moved forward from the front line. In the warm season, upward movements near the front line acquire a convective character, and cumulonimbus clouds often develop on warm fronts and showers and thunderstorms are observed (both during the day and at night).
in summer daytime hours V ground layer behind the line of a warm front, with significant cloudiness, the air temperature over land may be lower than in front of the front. This phenomenon is called masking of a warm front.
Cloud cover from old warm fronts can also be stratified throughout the front. Gradually these layers dissipate and precipitation stops. Sometimes a warm front is not accompanied by precipitation (especially in summer). This happens when the moisture content of warm air is low, when the level of condensation lies at a significant height. When the air is dry and especially in the case of its noticeable stable stratification, the upward sliding of warm air does not lead to the development of more or less intense cloudiness - that is, there are no clouds at all, or a strip of clouds of the upper and middle tiers is observed.
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See what a “Warm Front” is in other dictionaries:
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Atmospheric front (from other Greek: ατμός steam, σφαῖρα ball and Latin frontis forehead, front side), tropospheric fronts are a transition zone in the troposphere between adjacent air masses with different physical properties. An atmospheric front occurs when... ... Wikipedia
Atmospheric front (from other Greek: ατμός steam, σφαῖρα ball and Latin frontis forehead, front side), tropospheric fronts are a transition zone in the troposphere between adjacent air masses with different physical properties. An atmospheric front occurs when... ... Wikipedia
It turned out that warm air is drawn into the cyclone not throughout its entire eastern (right) half, but in a fairly limited sector located in the southern and southeastern parts of the cyclone between two convergence lines. Cloudiness and precipitation are distributed unevenly in the cyclone. Covering rains fall mainly in front of the first (eastern) line of convergence of air flows, as well as in the center of the cyclone. Showers and thunderstorms are concentrated in a narrow band along the second (western) convergence line. These lines were subsequently called atmospheric fronts. Since cyclones usually move from west to east in temperate latitudes, the observation point first passes Eastern front a cyclone followed by warm air. This atmospheric front was called a warm front. In the vicinity of a warm atmospheric front, warm air actively advances onto the front line, moves almost perpendicular to it, and cold air is transported almost parallel to this line, i.e. slowly retreats from her. Consequently, the warm air mass catches up and overtakes the cold one. Then the western (cold) front of the cyclone approaches the observation point, as it passes the air temperature drops sharply. Near a cold atmospheric front, the dynamics are different: cold air catches up with warm air and rapidly displaces it upward.
The upward sliding covers thick layers of warm air over the entire frontal surface and an extensive system of high-stratus clouds with overlying precipitation arises. The warm front has an anticyclonic curvature and moves towards the cold air. On a weather map, a warm front is marked in red or with blackened semicircles directed in the direction of the front’s movement (Fig. 1). As the warm front line approaches, pressure begins to drop, clouds thicken, and heavy precipitation begins to fall. In winter, low stratus clouds usually appear when a front passes. The temperature and humidity are slowly increasing. As a front passes, temperatures and humidity typically rise quickly and winds pick up. After the front passes, the direction of the wind changes (the wind turns clockwise), its speed decreases, the pressure drop stops and its slight increase begins, the clouds dissipate, and precipitation stops. The field of pressure trends is presented as follows: in front of the warm front there is a closed area of pressure drop, behind the front there is either an increase in pressure or a relative increase (a decrease, but less than in front of the front). The passage of a warm front is usually accompanied by a powerful layer of rain covering the entire sky with heavy rain. The first sign of a warm front is cirrus clouds. Gradually they turn into a continuous white veil of cirrostratus clouds. IN upper layers Warm air is already moving into the atmosphere. The pressure drops. The closer the front line is to us, the denser the clouds become. The sun shines through as a dim spot. Then the clouds drop lower and the sun disappears completely. The wind intensifies and changes its direction clockwise (for example, at first it was easterly, then southeasterly and even southwest). Approximately 300-400 km before the front, the clouds thicken. Light continuous rain or snow begins. But the warm front has passed. The rain or snow has stopped, the clouds are dissipating, warming is coming - a warmer air mass has arrived. The warm front in a vertical section is shown in Fig. 2.
If the warm air retreats and the cold air spreads out after it, it means that a cold front is approaching. His arrival always causes a chill. But when moving, not all layers of air have the same speed. The lowest layer as a result of friction against earth's surface is delayed a little, and the taller ones are pulled forward. Thus, cold air falls on warm air in the form of a shaft. Warm air is quickly forced upward and powerful piles of cumulus and cumulonimbus clouds are created. The clouds of the cold front carry showers, thunderstorms, accompanied by strong gusty winds. They can reach very high altitude, but in the horizontal direction they extend only 20...30 km. And since the cold front usually moves quickly, stormy weather does not last long - from 15...20 minutes. up to 2...3 hours. As a result of the interaction of cold air with the warm underlying surface, cumulus clouds with gaps are formed. Then comes complete clarity.
In the case of a cold front, the upward movement of warm air is limited to a narrower zone and is especially strong in front of the cold wedge, where warm air is displaced by cold air. The clouds here will be largely cumulonimbus with showers and thunderstorms (Fig. 3, Fig. 4). A cold front has a cyclonic curvature (bulges toward warm air) and moves toward warm air. On a weather map, a cold front is marked in blue or with blackened triangles directed in the direction the front is moving (Fig. 1). The flow in cold air has a component directed towards the front line, so cold air, moving forward, occupies the space where warm air was previously located, which increases its instability.
When crossing the line of a warm front, the wind, as in the case of a warm front, turns to the right, but the turn is more significant and sharp - from the southwestern, southern (in front of the front) to the western, northwestern (behind the front). At the same time, the wind speed increases. Atmospheric pressure changes slowly ahead of the front. It may fall, but it can also rise. With the passage of a cold front, a rapid increase in pressure begins. Behind the cold front there is a closed isallobaric region of pressure growth, and the increase can reach 3-5 hPa/3h. A change in pressure in the direction of its growth (from a decrease to an increase, from a slow increase to a stronger one) indicates the passage of the surface front line.
Thunderstorms and squalls are common ahead of the front. After the front passes, the air temperature drops, often quickly and sharply – by 10 °C or more in 1-2 hours. The mass fraction of water vapor decreases simultaneously with the air temperature. Visibility typically improves as polar or arctic air moves in behind the cold front. Moreover, the instability air mass prevents condensation near the Earth's surface.
The nature of the weather on a cold front varies markedly depending on the speed of the front's movement, the properties of warm air ahead of the front, and the nature of the upward movements of warm air above the cold wedge. Cold fronts of the 1st type are dominated by an orderly rise of warm air above a wedge of cold air. A type 1 cold front is a passive upward sliding surface. Slowly moving or slowing down their movement fronts belong to this type, mainly on the periphery of cyclonic regions in deep baric troughs. In this case, the clouds are located mainly behind the front line. There is still a difference from the cloudiness of a warm front. Due to friction, the surface of the cold front in the lower layers becomes steep. Therefore, just before the front line, instead of a calm and gentle upward sliding, a steeper (convective) rise of warm air is observed (Fig. 3). Due to this, powerful cumulus and cumulonimbus clouds sometimes appear in the front part of the cloud system, stretching for hundreds of kilometers along the front, with showers in summer, snowfall in winter, thunderstorms, hail and squalls. Over the overlying part of the frontal surface with a normal slope as a result of the upward sliding of warm air, the cloud system represents a uniform cover of stratus clouds. Rainfall ahead of the front after the passage of the front is replaced by more uniform blanket precipitation. Finally, cirrostratus and cirrus clouds appear. The vertical power of the system and the width of the cloud system and precipitation area will be almost 2 times less than in the case of a warm front. The upper boundary of the system is approximately at an altitude of 4-4.5 km. Stratus broken clouds may develop beneath the main cloud system, and frontal fogs may sometimes form. The duration of passage of a cold front of the 1st type through an observation point is 10 hours or more.
Fronts of the 2nd kind in the lower layer of the atmosphere are a passive ascending slip surface, and above them are an active downward sliding surface. Most fast-moving cold fronts in cyclones belong to this type. Here, the warm air of the lower layers is displaced upward by the cold shaft moving forward. The surface of the cold front in the lower layers is very steep, even forming a bulge in the form of a shaft (Fig. 4). The rapid movement of a wedge of cold air causes forced convection of displaced warm air in a narrow space at the front of the frontal surface. Here a powerful convective flow is created with the formation of cumulonimbus clouds, intensifying as a result of thermal convection. The harbingers of the front are altocumulus lentiform clouds, which spread in front of it at a distance of up to 200 km. The emerging cloud system has a small width (50-100 km) and does not represent individual convective clouds, but a continuous chain, or a cloud bank, which sometimes may not be continuous. In the warm half of the year, the upper boundary of cumulonimbus clouds extends to the height of the tropopause. On cold fronts of the 2nd type, intense thunderstorm activity, showers, sometimes with hail, and squally winds are observed. There is strong turbulence and icing in the clouds. The width of the zone of dangerous weather phenomena is several tens of kilometers. In the cold half of the year, the tops of cumulonimbus clouds reach 4 km. The width of the snowfall zone is 50 km. This cloudiness is associated with heavy snowfalls, blizzards with visibility less than 1000 m, a sharp increase in wind speed, and roughness.
When cold fronts of the 2nd type pass through an observation point, cirrus clouds first appear (3-4 hours before the front line passes near the Earth), which are quickly replaced by altostratus, sometimes lenticular, which are quickly replaced by a huge cloud with showers, thunderstorms, hail, and squalls. The duration of movement of a cloud system with showers and thunderstorms usually does not exceed 1-2 hours. After the cold front passes, the rainfall stops. A feature of cold fronts of both the first and second types are prefrontal squalls. Since in the front part of the cold wedge, due to friction, a steep slope of the frontal surface is created, part of the cold air appears above the warm one. Next, the cold air masses “collapse” down in the front part of the advancing cold shaft. The collapse of cold air leads to the displacement of warm air upward and to the appearance of a vortex with a horizontal axis along the front. Squalls on land are especially intense in the summer, when there is a large temperature difference between warm and cold air on both sides of the front and when warm air is unstable. Under these conditions, the passage of a cold front is accompanied by destructive wind speeds. The wind speed often exceeds 20-30 m/s, the duration of the phenomenon is usually several minutes, and gusts are sometimes observed.
Occlusion fronts
Due to downward movements in the cold air at the rear of the cyclone, the cold front moves faster than the warm front and over time catches up with it. At the stage of filling the cyclone, complex fronts arise - occlusion fronts, which are formed when cold and warm atmospheric fronts close.
In the occlusion front system, three air masses interact, of which the warm one no longer comes into contact with the Earth’s surface. The process of displacing warm air into the upper layers is called occlusion. In this case, the rear wedge of cold air of the cyclone closes with the front wedge of cold air. Warm air in the form of a funnel gradually rises upward, and its place is taken by cold air coming from the sides (Fig. 5). The interface that occurs when cold and warm fronts meet is called the occlusion front surface.
In the case of an occluded cold front, precipitation can occur on both sides of the lower front, and the transition from blanket precipitation to showers, if it occurs, occurs not ahead of the lower front, but in close proximity to it. In the case of a warm occlusion front, the vortex of warm air is displaced by warmer air flowing onto a wedge of colder air. The rear wedge of less cold air overtakes the front wedge of colder air, and the cold front, having separated from the Earth's surface, rises along the surface of the warm front.
A weak upward sliding of the rear air along the front along the occlusion surface can lead to the formation of St-Sc clouds along it, not reaching the level of the ice cores. These will produce some drizzle ahead of the lower warm front.
Special weather phenomena are associated with atmospheric fronts. On the one hand, the transition from one air mass to another is accompanied by sharp fluctuations in meteorological elements. On the other hand, ascending air movements in frontal zones lead to the formation of extensive cloud systems, from which precipitation falls over large areas, and huge atmospheric waves arising in air masses on both sides of the front lead to the formation of atmospheric disturbances - large-scale vortices - cyclones and anticyclones.
The peculiarities of atmospheric circulation are such that atmospheric fronts are constantly eroded and re-emerged. Together with them, air masses on both sides of the front are formed and change their properties (transformed).
The approach of atmospheric fronts can be traced quite reliably by certain signs.
Warm front
If a front moves in such a way that cold air retreats to give way to warm air, then such a front is called a warm front.
The angle of inclination of the warm front to the horizontal surface is about 0.5 ◦. There are two air masses vertically in the troposphere. Cold air remains a narrow wedge near the ground. Warm air rises along the frontal surface. Since the rise at all altitudes occurs slowly, stratus clouds form over vast areas. Warm air, moving forward, not only occupies the space where cold air used to be, but also rises along the transition zone. As the warm air rises, it cools and the water vapor in it condenses. As a result, clouds are formed, which are characterized by special cloudiness, precipitation and air currents of a warm front. The first sign of an approaching warm front will be the appearance of cirrus clouds (Ci). The pressure will begin to drop. After a few hours, the cirrus clouds thicken and become a veil of cirrostratus clouds (Cs). Following the cirrostratus clouds, even denser altostratus clouds (As) flow in, gradually becoming opaque to the moon or sun. At the same time, the pressure drops more strongly, and the wind, turning slightly to the left, intensifies. Precipitation can fall from high-stratus clouds, especially in winter, when they do not have time to evaporate along the way.
After some time, these clouds turn into nimbostratus (Ns), under which there are usually stratus clouds (Fr nb) and stratus clouds (St fr). Precipitation from nimbostratus clouds falls more intensely, visibility deteriorates, pressure drops quickly, the wind increases and often becomes gusty. As the front crosses, the wind turns sharply to the right and the pressure drop stops or slows down. Precipitation may stop, but usually it only weakens and turns into drizzling. The temperature and humidity are gradually increasing.
After the front passes, the temperature increases and precipitation stops. In winter, visibility may remain poor due to advective fog in the warm air. Possible drizzle. IN summer time visibility behind the front line improves. Before a warm front, pressure drops.
Signs that a warm front is approaching are a drop in pressure, an increase in density, water content of clouds, a decrease in their lower boundary, the appearance of nimbostratus, heavy precipitation, the appearance of fragments of stratus fractus (St, fr) or fractonimbus ().
The difficulties that can be encountered when crossing a warm front are mainly associated with prolonged exposure to a zone of poor visibility, the width of which ranges from 150 to 200 miles.
During the cold season, precipitation in the form of snow or snow pellets may fall from altostratus clouds 400 km before the front. In summer, the precipitation zone narrows to 300 km, since precipitation in the form of light rain or drizzle from As evaporates in the warm air without reaching the underlying surface.
Cold front
When a cold air mass replaces a warm one, the line along which the frontal surface intersects the horizontal surface at sea level is called a cold front.
A cold front is a front moving towards a warm air mass. There are two main types of cold fronts:
1) cold fronts of the first kind - slowly moving or slowing fronts, which are most often observed on the periphery of cyclones or anticyclones;
2) cold fronts of the second type - rapidly moving or moving with acceleration; they arise in the internal parts of cyclones and troughs moving at high speed.
On a cold front of the first type, warm air rises rather slowly up the cold wedge. In this case, warm air slowly rises up the wedge of cold air invading underneath it. Above the zone of separation of air masses, nimbostratus (Ns) clouds first form, turning at some distance behind the front into altostratus (As) and cirrostratus (Cs) clouds. Precipitation falls directly on the front line and behind the front. The width of the precipitation zone usually does not exceed 50–120 miles. In summer, powerful cumulonimbus (Cb) clouds form over the oceans in particularly deep cyclones and in winter in the front part of a cold front of the first kind, from which rainfall falls, accompanied by thunderstorms. Atmospheric pressure drops sharply ahead of the front, and rises behind the front. At the same time, there is a turn of the wind to the left before the front and a sharp turn to the right behind the front. The wind changes its direction especially sharply (sometimes by 180°) when the front is located near the axis of a narrow trough. As the front passes, cold weather sets in. Sailing conditions when crossing a cold front of the first type will be affected by deteriorating visibility in the precipitation zone and squally winds.
On a cold front of the second kind, the rapid movement of cold air leads to the development of intense convective movement of the prefrontal thermal humid air and, consequently, to the powerful development of cumulus (C) and cumulonimbus (Cb) clouds.
At high altitudes (at the tropopause), cumulonimbus clouds extend forward 50 to 80 miles from the front line. The leading part of the cloud system of a cold front of the second type is observed in the form of cirrostratus (Cs), cirrocumulus (Cc), and lenticular altocumulus (Ac) clouds. Useful and fairly timely information about an approaching cold front can be obtained using ship radars.
Atmospheric pressure drops slowly ahead of a cold front of the second type, and rises rapidly behind the front line. The wind turns to the left, and behind the front it sharply turns to the right and often intensifies into a storm. There will be showers ahead of and at the front, and thunderstorms are possible. In the warm season, at some distance from the front (in a cold air mass), the formation of a secondary cold front with showers and thunderstorms is possible.
Navigation conditions when crossing such a front are unfavorable, because near the front line, powerful ascending air currents contribute to the formation of a vortex with destructive wind speeds. The width of such a zone can reach 30 miles.
Occlusion fronts
A front consisting of two fronts and formed in such a way that a cold front overlaps a warm or stationary front is called an occlusion front. Complex complex fronts - occlusion fronts are formed by the closure of cold and warm fronts during the occlusion of cyclones. A cold front follows a warm front. A cold front typically moves quickly. Over time, it catches up with the warm one and the fronts close.
This is a common process in the last stage of a cyclone's development, when a cold front catches up with a warm one. There are three main types of occluded fronts, caused by the relative coolness of the air mass following the initial cold front to the air ahead of the warm front. These are the fronts of cold, warm and neutral occlusion.
A distinction is made between a warm front of occlusion, when the air behind a cold front is warmer than the air in front of a warm front, and a cold front of occlusion, when the air behind a cold front is colder than the air in front of a warm front.
Occlusion fronts go through a number of stages in their development. The most difficult weather conditions on occluded fronts are observed at the initial moment of closure of the warm and cold fronts. During this period, the cloud system is a combination of warm and cold front clouds. Precipitation of a blanket nature begins to fall from nimbostratus and cumulonimbus clouds; in the frontal zone they turn into showers.
The wind intensifies before the warm front of the occlusion, weakens after passing and turns to the right.
Before the cold front of occlusion, the wind intensifies to a storm, after passing it weakens and sharply turns to the right. As warm air is displaced into higher layers, the occlusion front gradually blurs, the vertical power of the cloud system decreases, and cloudless layers appear. Nimbostratus clouds gradually change to stratus, altostratus to altocumulus, and cirrostratus to cirrocumulus. Precipitation stops. The passage of old occlusion fronts is manifested in the influx of altocumulus clouds of 7-10 points.
The conditions for swimming through occlusion fronts in the initial stage of development are almost no different from the conditions for swimming when crossing warm or cold fronts, respectively.
In their development, occlusion fronts go through three stages. Particularly difficult weather conditions on fronts are observed at the moment of closure of warm and cold fronts. A cloud system is a complex combination of clouds associated with both warm and cold fronts. Pre-frontal cover precipitation from nimbostratus and cumulonimbus clouds turns into showers directly in the front zone. The direction and speed of the wind when passing occlusion fronts change in the same way as on simple fronts. Over time, warm air is forced upward and the occlusion front is gradually eroded, the vertical power of the cloud system decreases and gaps appear in the cloud cover. At the same time, nimbostratus clouds gradually transform into stratus, altostratus into altocumulus, and cirrostratus, in turn, into cirrocumulus. This restructuring of cloud systems causes precipitation to cease.
Hydrometeorological conditions of navigation in the zones of occlusion fronts differ slightly from the conditions of navigation during the passage of simple fronts: cold or warm.
A cloud system is a complex combination of clouds associated with both warm and cold fronts. Weather conditions during the passage of such fronts are also unfavorable for yachtsmen - they are accompanied by rain with thunderstorms and hail, strong and gusty winds with sudden changes in directions and, at times, poor visibility.
Pre-frontal cover precipitation from nimbostratus and cumulonimbus clouds turns into showers directly in the front zone. The direction and speed of the wind when passing occlusion fronts change in the same way as on simple fronts. Over time, warm air is forced upward and the occlusion front is gradually eroded, the vertical power of the cloud system decreases and gaps appear in the cloud cover. At the same time, nimbostratus clouds gradually transform into stratus, altostratus into altocumulus, and cirrostratus, in turn, into cirrocumulus. This restructuring of cloud systems causes precipitation to cease.
Slowly moving or stationary fronts
A front that does not experience a noticeable displacement either towards the warm or towards the cold air mass is called stationary.
Stationary fronts are usually located in a saddle, or in a deep trough or on the periphery of an anticyclone. The cloud system of a stationary front is a system of cirrostratus, altostratus, and nimbostratus clouds that looks similar to that of a warm front. In summer, cumulonimbus clouds often form at the front.
The direction of the wind at such a front remains almost unchanged. The wind strength on the cold air side is less. The pressure does not experience significant changes. In a narrow band (30 miles) heavy rain falls.
Wave disturbances can form at a stationary front. The waves move quickly along the stationary front in such a way that the cold air remains to the left, that is, in the direction of the isobars in the warm air mass. The travel speed reaches 30 knots or more.
After the wave passes, the front restores its position. An increase in wave disturbance before the formation of a cyclone is observed, as a rule, if cold air flows from the rear.
In spring and autumn, and especially in summer, the passage of waves on a stationary front causes the development of intense thunderstorm activity, accompanied by squalls.
Navigation conditions when crossing a stationary front are complicated due to deterioration of visibility, and in the summer - due to increased winds to stormy winds.
We looked at the warm front of the cyclone. Now let's turn our attention to the cold front. Let us analyze the features and external manifestations that allow yachting to prepare for its approach. Cold areas are parts of the main front that move towards a relatively warm air mass. Behind the cold front cold air mass moves. If the air flow is directed from a cold air mass to a warmer one, then such a front is called a cold front. The lag of the lower layers of air from the upper ones under the influence of friction with the earth's surface leads to the fact that the upper layers collapse down and take the form of a rolling shaft. Warm air forced straight upward rises quickly and forms a bank of dark clouds - cumulonimbus clouds. Depending on the speed of air movement, cold fronts of the first kind (the speed of movement is low) and the second kind are distinguished.
Cold front structure.
The structure of a cold front varies depending on whether it is moving quickly or slowly. For this reason they distinguish:
- a cold front of the first kind - a slow-moving one, in which cloudiness and precipitation are located mainly behind the front line, which makes it difficult for yachting to detect its approach;
- a cold front of the second type - a fast-moving front, in which clouds and precipitation are located mainly in front of the front line.
Cold fronts of the second kind are observed in the central part of the cyclone, and cold fronts of the first kind are observed at its periphery.
Cold front of the first kind.
During a cold front of the first kind, masses of warm air are displaced by a wedge of cold air invading it. Here the cloud pattern is a mirror image of the cloud cover. Immediately ahead of the line of the cold atmospheric front, cumulonimbus clouds (Cb) appear, from which rainfall falls, accompanied by thunderstorms. The width of the rain cloud zone is several tens of kilometers.
The Mz-Az cloud system with heavy precipitation is located behind the cold front line. The width of the cloud zone, its thickness and, accordingly, the width of the precipitation zone is approximately half that of a warm one. Thus, unlike a warm one, the cloud system of a cold front of the first kind does not allow yachtsmen to detect its approach in advance by looking at the clouds.
Cold front of the second kind.
A cold front of the second type is characterized by the fact that fast travel the air shaft causes a rapid rise of pushed-back warm air in front of the front line, and downward movements of air flows prevent the spread of the cloud system directly behind the front line. The emerging cloud system is basically a shaft of powerful Cb clouds. When they spread in small quantities, Cc, Ac and Sc can form, and under them, in the zone of heavy rainfall, broken cumulus are usually observed bad weather. At altitudes of 4-5 km, the upward flow of adiabatically cooled moist air meets the downward flow of adiabatically heated dry air. As a result, an upper secondary front is formed, under which the cloud bank Cb is pulled forward. Its leading edge, which has the character of Az, can gradually divide into ridges of lenticular clouds As. These clouds are carried forward 200 - 300 km and their detection is a reliable warning in yachting about the approach of a cold front of the second kind.
Behind the line of the cold atmospheric front, downward air movements are observed in the air mass, especially significant in the front part of the air wedge. Therefore, intramass clouds do not appear here. Soon after the passage of the cold front line, rapid clearing occurs, up to complete clearing; only after a few hours, when the downward movements die out and the frontal surface rises sufficiently, convective clouds and rainfall, characteristic of an unstable mass, may appear.
Rainfall during the passage of a cold front of the second type is short-lived (from several minutes to 1 hour), since the width of the precipitation zone is small and the speed of movement is significant. In the bank of cumulonimbus clouds there are sometimes gaps or less developed clouds in the lower and middle layers. In some areas, thunderstorm activity develops, which, having died out in some areas, may appear in neighboring ones.
The direction of the wind during the passage of cold fronts of both types changes in the same way as in the case of a warm one, but the turn to the right (in the northern hemisphere) at the moment of passage is more significant and sharp. At the same time, the wind speed increases sharply.
As a cold front approaches, there is a short, usually weak, but gradually accelerating drop in pressure. Immediately after passage, pressure begins to increase due to the replacement of warm air with cold air.
The air temperature decreases after the passage of the cold front line. The temperature jump depends on the nature of the changing masses.
Cold fronts of both types are characterized by prefrontal squalls, especially dangerous phenomena for yachting. Air behind a cold front is characterized by downward movement, which becomes especially intense in the front part of the wedge, where friction creates a steep slope of the frontal surface. The air, falling down, seems to roll forward, like the tracks of a tank, and the speed of its movement in all cases turns out to be greater than the corresponding component of the speed of warm air in the lower layers. The collapse of cold air leads to the displacement of warm air upward and to the appearance of a vortex with a horizontal axis; The phenomena of frontal squalls are associated with this vortex.
Particularly intense downward movement occurs at the head of cold air. Falling from a height of several kilometers, this air is adiabatically heated, and due to this the temperature jump is smoothed out. In some cases, a secondary cold front appears within the cold wedge, separating the heated air of the “head” from the air that lies further away and is not captured to the same extent by the downward movement.
This second cold front is several kilometers behind the eroded main one. During its passage, a jump in temperature, winds and squalls are observed, but it does not have a cloud system. This phenomenon is called the bifurcation of a cold front. Boaters should keep this in mind and not become complacent after the passage of a cold front. Squalls without a visible cloud system can cause many problems in yachting. As they say, he crept up unnoticed.
Secondary cold fronts usually form in pressure troughs in the rear of a cyclone. They have a cloud system similar to the cloud system of a cold front of the second type, but the vertical extent of the clouds in them is less than the extent of the clouds of the main fronts. In some cases there may be several troughs and secondary fronts.
Sedentary (stationary) are sections of the main front that do not undergo significant movement.
In a cyclone, the cold front moves slightly faster than the warm front. Over time, they come closer together and then merge, starting near the center of the cyclone. Such a front, formed as a result of the merging of cold and warm, is called an occlusion (closed) front. But more about this in.