A shower is a mode of

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

characterized by an abrupt start and end and by rapid variations in intensity. Often strong and short-lived, it comes from convective clouds, like cumulus congestus. A shower will produce

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...

if the temperature is above the freezing point in the cloud, or

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughou ...

ice pellets Ice pellets are a form of precipitation consisting of small, hard, translucent balls of ice. Ice pellets are different from graupel ("soft hail") which is made of frosty white opaque rime, and from a mixture of rain and snow which is a slushy ...

/ snow pellets /

hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...

if the temperature is below it at some point. In a meteorological observation, such as the

METAR METAR is a format for reporting weather information. A METAR weather report is predominantly used by aircraft pilots, and by meteorologists, who use aggregated METAR information to assist in weather forecasting. Raw METAR is the most common fo ...

, they are noted SH giving respectively SHRA, SHSN, SHPL, SHGS and SHGR.

Formation

Convection occurs when the Earth's surface, especially within a conditionally unstable or moist

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...

, becomes heated more than its surroundings and in turn leading to significant evaporation. The raised

air parcel In fluid dynamics, within the framework of continuum mechanics, a fluid parcel is a very small amount of fluid, identifiable throughout its dynamic history while moving with the fluid flow. As it moves, the mass of a fluid parcel remains constant, ...

in a colder environment at altitude will cool but according to the adiabatic thermal gradient forming clouds, and later precipitation above the

lifted condensation level The lifted condensation level or lifting condensation level (LCL) is formally defined as the height at which the relative humidity (RH) of an air parcel will reach 100% with respect to liquid water when it is cooled by dry adiabatic lifting. The ...

(LCL). Depending on the

Convective available potential energy In meteorology, convective available potential energy (commonly abbreviated as CAPE), is the integrated amount of work that the upward (positive) buoyancy force would perform on a given mass of air (called an air parcel) if it rose vertically thro ...

(CAPE), the clouds will be cumulus humilis, cumulus mediocris and then cumulus congestus, the latter giving short-lived precipitation of rain, snow or ice pellets changing in intensity, i.e. showers. The life cycle of these clouds is fast because the updraft which forms them is most often cut off by the descent of precipitation. In addition, these clouds flow with atmospheric circulation and spend little time above a point on the ground. This explains the variations in intensity and the short duration of the showers. The type of precipitation will depend on the temperature structure in the cloud and below it: *In winter, when the temperature in the cloud is below freezing (0 °C), snowflakes will be generated: **They will melt and give raindrops if the temperature rises above it in a deep layer between the cloud and the ground. If the layer is not deep enough, it can produce snow pellets showers. **Or remain as snow showers, or flurry, if the temperature remains below freezing. *On the other hand, raindrops might form in a strong updraft in a convective cloud, even at temperature below freezing in the cloud (

Supercooling Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its melting point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crystal ...

) and freeze later, giving ice pellet showers. *Finally, droplets can form and fall in an above freezing layer in other seasons, giving rain showers.

Extreme

If the convection is more intense, it leads to the formation of

cumulonimbus cloud Cumulonimbus (from Latin ''cumulus'', "heaped" and ''nimbus'', "rainstorm") is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. ...

s which have a very large vertical extension. This permits the displacement of electric charges from the bottom to the top that will create lightning and thunder. The showers associated with this kind of clouds are therefore called ''thundershowers'' or ''

thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are some ...

s''.

Hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...

and other violent phenomena are associated with this type of convection.

Showery systems

Showers come from individual clouds as well as from groups of these. In mid-latitude regions, showers are often associated with

cold front A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface trough of low pressure. It often forms behind an extratropical cyclone (to the west in the Northern ...

s, often found along and behind it. However they can be embedded into a continuous rain episode when there is presence of band of conditional symmetric instability in an otherwise stable air mass. They can also be part of large convection zones called

mesoscale convective system A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more. A mesoscale con ...

such as a

squall line A squall line, or more accurately a quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accom ...

Formation

Extreme

Showery systems

References

See also