A shower is a mode of

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

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 Cumulus congestus or towering cumulus clouds are a species of cumulus that can be based in the low- to middle-height ranges. They achieve considerable vertical development in areas of deep, moist convection. They are an intermediate stage between ...

. A shower will produce

rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...

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

snow Snow consists of 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 througho ...

ice pellets Ice pellets ( Commonwealth English) or sleet (American English) is 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, a ...

snow pellets Graupel (; ), also called soft hail or hominy snow or granular snow or snow pellets, is precipitation that forms when supercooled water droplets in air are collected and freeze on falling snowflakes, forming balls of crisp, opaque rime. Graupe ...

hail Hail is a form of solid Precipitation (meteorology), 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 hailsto ...

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 highly standardize ...

, 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 gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

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

air parcel In fluid dynamics, a fluid parcel, also known as a fluid element or material element, is an infinitesimal volume of fluid, identifiable throughout its dynamic history while moving with the fluid flow. As it moves, the mass of a fluid parcel remain ...

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

lifted condensation level The lifting condensation level or lifted condensation level (LCL) is 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 RH of air increases ...

(LCL). Depending on the convective available potential energy (CAPE), the clouds will form in order: cumulus humilis, cumulus mediocris and then

, 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 into raindrops if the temperature rises above freezing in a deep layer between the cloud and the ground. If the layer is not deep enough, it can produce snow pellet 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 temperatures below freezing in the cloud (

Supercooling Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. Per the established international definition, supercooling means ''‘cooling a substance be ...

) 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 () 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. Above the lower portions of the cumulonimbus the water ...

s, which have a very high vertical extent. The size of such clouds permits the displacement of electric charges from the bottom to the top, which produce lightning and its associated thunder. The showers associated with cumulonimbus 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 acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...

s'', which, along with heavy rain, can also produce

and other violent phenomena.

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 (meteorology), trough of Low-pressure area, low pressure. It often forms behind an extratropica ...

s, often found along and behind them. However, they can be embedded into a continuous rain episode when a band of

conditional symmetric instability Conditional symmetric instability, or CSI, is a form of convective instability in a fluid subject to temperature differences in a uniform rotation frame of reference while it is thermally stable in the vertical and dynamically in the horizontal (in ...

is present 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 conv ...

s, such as a

squall line A squall line, or 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 accompanied by abrupt a ...

Formation

Extreme

Showery systems

References

See also