A squall is a sudden, sharp increase in wind speed which is usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. A rainbow is an optical and meteorological phenomenon that causes a spectrum of Light to appear in the Sky when the Sun ^[1] Squalls refer to an increase in the sustained winds over a short time interval, as there may be higher gusts during a squall event. ^[2] They usually occur in a region of strong mid-level height falls, or mid-level tropospheric cooling, which force strong localized upward motions at the leading edge of the region of cooling, which then enhances local downward motions just in its wake.

Contents 1 Origin of the term 2 Character of the wind 3 Regional terms 3.1 Argentina 3.2 Central America 3.3 Cuba 3.4 East Indies 3.5 Pacific Northwest - United States 3.6 South Africa 3.7 Southeast Asia 4 Severe weather 4.1 Squall Line Life Cycle 4.1.1 Squall Line Formation 4.1.1.1 Updrafts 4.1.1.2 Pressure Perturbations 4.1.1.3 Wind Shear 4.1.2 Squall Line Evolution 4.1.2.1 Updrafts 4.1.2.2 Bow Echoes 4.1.2.3 Mesolow 4.1.3 Squall Line Dissipation 4.2 Signs in the sky 5 Tropical cyclones 6 Winter weather 7 Literary usage 8 See also 9 References

Origin of the term

The word appears to be Nordic in origin, but its etymology is considered obscure. Etymology is the study of the History of Words &mdash when they entered a language from what source and how their form and meaning have changed over time It probably has its roots in the word skvala^[3] an Old Norse word meaning literally, to squeal. ^[4] The first known use of the term on surface weather analyses was in the United States in the late Nineteenth Century on U. A 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 The United States of America —commonly referred to as the S. Signal Corp Maps, begun in 1871.

Character of the wind

The term "squall" is universally used to refer to a sudden wind-speed increase, both historically and in the present day. To be called a squall in the United States, the wind must increase at least 18 miles per hour (8 meters per second) and must attain a top speed of at least 25 miles per hour (11 meters per second), lasting at least a full minute in duration. The United States of America —commonly referred to as the In Australia, a squall is defined to last for several minutes before the wind returns to the long term mean value. For a topic outline on this subject see List of basic Australia topics. In either case, a squall is defined to last about half as long as the definition of sustained wind in its respective country. Usually, this sudden violent wind is often associated with briefly heavy precipitation.

Regional terms

Argentina

Known locally as pamperos, they are used to describe strong downsloped winds that move across the pampas, eventually making it to the Atlantic Ocean. ^[5]

Central America

Offshore Central America, the term gully squall is used to describe strong increases of the wind forced through sharp mountain valleys on the Pacific Ocean side of the isthmus. The Pacific Ocean is the largest of the Earth 's Oceanic divisions

Cuba

Bayamo is a term used to describe squalls emanating from tropical thunderstorms near the Bight of Bayamo. In Geography, bight has two meanings A bight can be simply a bend or curve in any geographical feature&mdashusually a bend or curve in the line between land ^[6]

East Indies

In the East Indies, brubu is a name for a squall^[7]

Pacific Northwest - United States

In the Pacific Northwest, a squall is a short but furious rainstorm with strong winds, often small in area and moving at high speed, especially as a maritime term. The Indies or East Indies (or East India) is a term often used to refer to the islands of SE Asia, especially the Malay Archipelago The Pacific Northwest is a region in the northwest of North America (the term refers to the land not the ocean Such a strong outflow occurring in fjords and inlets is referred to by mariners as a squamish. A squamish (also known as an Arctic outflow wind in Winter months is a strong and often violent Wind occurring in many of the Fjords, inlets

South Africa

Bull's Eye Squall is a term used offshore South Africa, describing a squall forming in fair weather. It is named for the appearance of the small isolated cloud marking the top of the squall. ^[8]

Southeast Asia

Barat is a term for a northwest squall in Manado Bay in Sulawesi. Sulawesi (formerly known as Celebes, ˈsɛlɛbiz is one of the four larger Sunda Islands of Indonesia and is situated between Borneo and the ^[8]

Severe weather

A squall line is an organized line of thunderstorms. It is classified as a multi-cell cluster, meaning a thunderstorm complex comprising many individual updrafts. They are also called multi-cell lines. Squalls are sometimes associated with hurricanes or other cyclones, but they can also occur independently. A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding In Meteorology, a cyclone refers to an area of closed circular fluid motion rotating in the same direction as the Earth. Most commonly, independent squalls occur along front lines, and may contain heavy precipitation, hail, frequent lightning, dangerous straight line winds, and possibly funnel clouds, tornadoes and waterspouts. A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena. In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric Hail is a form of precipitation which consists of balls or irregular lumps of ice (hailstones Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or A funnel cloud is a Funnel -shaped Cloud of condensed Water droplets associated with a rotating column of air and extending from the base of A tornado is a violent rotating column of air which is in contact with both the surface of the earth and a Cumulonimbus cloud or in rare cases the base of a Cumulus A waterspout is an intense columnar Vortex (usually appearing as a Funnel -shaped Cloud) that occurs over a Body of water and is connected to ^[9] Squall lines require significant low-level warmth and humidity, a nearby frontal zone, and vertical wind shear from an angle behind the frontal boundary. ^[10] The strong winds at the surface are usually a reflection of dry air intruding into the line of storms, which when saturated, falls quickly to ground level due to its much higher density before it spreads out downwind. ^[11] In England, a squall associated with tempestuous weather is known as a blunk. Significant squall lines with multiple bow echoes are known as derechos. ^[12]

Squall Line Life Cycle

There are several forms of mesoscale meteorology, including simplistic isolated thunderstorms unrelated to advancing cold fronts, to the more complex daytime/nocturnal Mesoscale Convective System (MCS) and Mesoscale Convective Complex (MCC), to squall line thunderstorms. Mesoscale Meteorology is the study of Weather systems smaller than Synoptic scale systems but larger than microscale and Storm-scale cumulus A mesoscale convective system ( MCS) is a complex of Thunderstorms that becomes organized on a scale larger than the individual thunderstorms and normally persists A mesoscale convective complex (MCC is a unique kind of Mesoscale convective system which is defined by characteristics observed in infrared Satellite imagery. A squall line is a line of severe thunderstorms that can form along and/or ahead of a Cold front.

Squall Line Formation

The main driving force behind squall line creation is attributed to the process of in-filling of multiple thunderstorms and/or a single area of thunderstorms expanding outward within the leading space of an advancing cold front. A cold front defined as the leading edge of a cooler and drier mass of air

Updrafts

The leading area of a squall line is composed primarily of multiple updrafts, or singular regions of an updraft, rising from ground level to the highest extend of the troposhere, condensing water and building a dark, ominous clouds to one with a noticeable overshooting top and anvil (thanks to synoptic scale winds). An updraft or downdraft ( air pocket) is the vertical movement of Air as a Weather related phenomenon The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and The synoptic scale in Meteorology (also known as large scale or cyclonic scale) is a horizontal length scale of the order of 1000 kilometres (about 620 Because of the chaotic nature of updrafts and downdrafts, pressure perturbations are important. An updraft or downdraft ( air pocket) is the vertical movement of Air as a Weather related phenomenon

Pressure Perturbations

Pressure perturbations within an extent of a thunderstorm are noteworthy. With buoyancy rapid within the lower and mid-levels of a mature thunderstorm, one might believe that low pressure dominates in the mesoscale environment. In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is However, this is not the case. With downdrafts ushering colder air from mid-levels, hitting ground and propagating away in all directions, high pressure is to be found at surface levels, usually indicative of strong (potentially damaging winds).

Wind Shear

Wind shear is an important aspect to measuring the potential of squall line severity and duration. In low to medium shear environments, mature thunderstorms will contribute modest amounts of downdrafts, enough to turn will aid in create a leading edge lifting mechanism - the gust front. In high shear environments created by opposing low level jet winds and synoptic winds, updrafts and consequential downdrafts can be much more intense (common in supercell mesocyclones). The cold air outflow leaves the trailing area of the squall line to the mid-level jet, which aids in downdraft processes.

Squall Line Evolution

Updrafts

As thunderstorms fill into a distinct line, strong leading-edge updrafts - occasionally visible to a ground observer in the form of a shelf cloud, appear as an ominous sign of potential severe weather.

Beyond the strong winds because of updraft/downdraft behavior, heavy rain (and hail) is another sign of a squall line. Hail is a form of precipitation which consists of balls or irregular lumps of ice (hailstones In the winter, squall lines can occur albeit less frequently - bringing heavy snow and/or thunder and lightning - usually over inland lakes (i. Winter is one of the four Seasons of Temperate zones Calculated astronomically, it begins on the Solstice and ends on the Equinox "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. Thunder is the sound made by Lightning. Depending on the nature of the lightning and distance of the listener it can range from a sharp A lake (from Latin lacus) is a Terrain feature (or Physical feature) a body of Liquid on the surface of a world that is localized to the e. Great Lakes region). The Laurentian Great Lakes are a chain of freshwater lakes located in eastern North America, on the Canada–United States border.

Bow Echoes

Following the initial passage of a squall line, light to moderate stratiform precipitation is also common. Stratus means layer or blanket in Latin A Stratus cloud (St is a Cloud belonging to a class characterized by horizontal layering with a uniform base A Bow echo is frequently seen on the northern and southern most reaches of squall line thunderstorms (via satellite imagery. A bow echo is a term describing the characteristic radar return from a Mesoscale convective system that is shaped like an archer’s bow. This is where the northern and southern ends curl backwards towards the middle portions of the squall line, making a "bow" shape. A squall line is a line of severe thunderstorms that can form along and/or ahead of a Cold front. Bow echoes are frequently featured within supercell mesoscale systems. A supercell is a severe thunderstorm with a deep continuously rotating updraft (a Mesocyclone)

Mesolow

The northern end of the squall line is commonly referred to as the cyclonic end, with the southern side rotating anticyclonically. Because of the coriolis force, the northern end may evolve further, creating a "comma shaped" mesolow, or may continue in a squall-like pattern. In physics the Coriolis effect is an apparent deflection of moving objects when they are viewed from a Rotating frame of reference.

Squall Line Dissipation

As supercell or multi-cell thunderstorms disappate because of a weak shear, poor lifting mechanisms: (e. g. considerable terrain or lack of daytime heating. Terrain, or relief, is the third or vertical dimension of land surface. The squall line associated gust front may outrun the squall line, the synoptic scale low may fill - leading to a weaking of a cold front, or the thunderstorm has exhausted its updrafts, becoming purely a downdraft dominated system. A squall line is a line of severe thunderstorms that can form along and/or ahead of a Cold front. An outflow boundary is a Storm-scale or mesoscale boundary separating Thunderstorm -cooled air ( outflow) from the surrounding Air; The areas of disappating squall line thunderstorms may be regions of low CAPE, low humidity, insufficient wind shear, or poor synoptic dynamics (e. In Meteorology, convective available potential energy ( CAPE) sometimes simply available potential energy ( APE) is the amount of Energy Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity. g. an upper level low filling) leading to frontolysis. Frontolysis - in Meteorology, is the dissipation or weakening of an atmospheric front

From here, a general thinning of a squall line will occur: within, winds decaying with time, outflow boundaries weakening updrafts substantially, and clouds losing their thickness.

Signs in the sky

Shelf clouds and roll clouds are usually seen above the leading edge of a squall, also known as a thunderstorm's gust front. ^[13] From the time these low cloud features appear in the sky, one can expect a sudden increase in the wind in less than 15 minutes.

Tropical cyclones

Tropical cyclones normally have squalls coincident with spiral bands of greater curvature than many mid-latitude systems due to their smaller size. A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding This squalls can harbor waterspouts and tornadoes due to the significant vertical wind shear which exists in the vicinity of a tropical cyclone's outer bands. A waterspout is an intense columnar Vortex (usually appearing as a Funnel -shaped Cloud) that occurs over a Body of water and is connected to A tornado is a violent rotating column of air which is in contact with both the surface of the earth and a Cumulonimbus cloud or in rare cases the base of a Cumulus Wind shear, sometimes referred to as windshear or Wind gradient, is a difference in Wind speed and direction over a relatively

Winter weather

Snow squalls can be spawned by an intrusion of cold air aloft over a relatively warm surface layer. A snowsquall is a sudden moderately heavy Snow fall with Blowing snow and strong gusty surface Winds ref> National Weather Service Detroit/Pontiac Lake effect snows can be in the form of a snow squall. Lake-effect snow is produced in the winter when cold Arctic winds move across long expanses of warmer lake water providing energy and picking up Water vapor which freezes In Scotland, snow squalls are known as bluffarts. Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain.

Literary usage

Squall is a vocabulary word in the book Sarah, Plain and Tall in the title of the book "White Squall", written by John Conroy Hutcheson in 1900. Sarah Plain and Tall is a Children's book written by Patricia MacLachlan, and the winner of the 1986 Newbery Medal. ^[14]

See also

• Freak wave
• Squall line
• White squall

References

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