A rainband is a

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

and

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 hai ...

structure associated with an area of rainfall which is significantly elongated. Rainbands can be

stratiform Stratiform may refer to: * Any of the stratus family of clouds (fog, stratus clouds, altostratus clouds, cirrostratus clouds, nimbostratus clouds) and the precipitation coming from them. * Any occurrence of layered strata (see stratigraphic unit). ...

or convective, and are generated by differences in temperature. When noted on

weather radar Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly puls ...

imagery, this precipitation elongation is referred to as banded structure. Rainbands within tropical cyclones are curved in orientation. Rainbands of

tropical cyclones A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Dep ...

contain showers and thunderstorms that, together with the eyewall and the

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

, constitute a hurricane or tropical storm. The extent of rainbands around a tropical cyclone can help determine the cyclone's intensity. Rainbands spawned near and ahead of

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 can be

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 accompa ...

s which are able to produce

tornado A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, alt ...

es. Rainbands associated with cold fronts can be warped by mountain barriers perpendicular to the front's orientation due to the formation of a low-level barrier jet. Bands of thunderstorms can form with

sea breeze A sea breeze or onshore breeze is any wind that blows from a large body of water toward or onto a landmass; it develops due to differences in air pressure created by the differing heat capacities of water and dry land. As such, sea breezes ar ...

and land breeze boundaries, if enough moisture is present. If sea breeze rainbands become active enough just ahead of a cold front, they can mask the location of the cold front itself. Banding within the comma head precipitation pattern of an extratropical cyclone can yield significant amounts of

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 ...

snow Snow comprises individual ice crystals that grow while suspended in the 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 ...

. Behind extratropical cyclones, rainbands can form downwind of relative warm bodies of water such as the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five la ...

. If the atmosphere is cold enough, these rainbands can yield heavy

Extratropical cyclones

Rainbands in advance of warm

occluded front In meteorology, an occluded front is a type of weather front formed during cyclogenesis. The classical and usual view of an occluded front is that it initiates when a cold front overtakes a warm front near a cyclone, such that the warm air is se ...

s and

warm front A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold fr ...

s are associated with weak upward motion, and tend to be wide and stratiform in nature. In an atmosphere with rich low level moisture and vertical

wind shear Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizon ...

, narrow, convective rainbands known as

s form generally in the cyclone's warm sector, ahead of strong cold fronts associated with extratropical cyclones. Wider rain bands can occur behind cold fronts, which tend to have more stratiform, and less convective, precipitation. Within the cold sector north to northwest of a cyclone center, in colder cyclones, small scale, or mesoscale, bands of heavy snow can occur within a cyclone's comma head precipitation pattern with a width of to . These bands in the comma head are associated with areas of frontogensis, or zones of strengthening temperature contrast. Southwest of

extratropical cyclones Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of p ...

, curved flow bringing cold air across the relatively warm

can lead to narrow

lake-effect snow Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water. The lower layer of air, heated up by the lake water, picks up water vapor from the lake and rises up through ...

bands which bring significant localized snowfall.

Narrow Cold Frontal Rainband

A narrow cold frontal rainband (NCFR) is a characteristic of particularly sharp cold frontal boundaries. These can usually be seen very easily on satellite photos. NCFRs are typically accompanied by strong gusty winds and brief but intense rainfall. Convection may or may not occur depending on the stability of the air mass being lifted by the front. Such fronts usually are also marked by a sharp wind shift and temperature drop.

Tropical cyclones

Rainbands exist in the periphery of tropical cyclones, which point towards the cyclone's center of

low pressure In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...

. Rainbands within tropical cyclones require ample moisture and a low level pool of cooler air. Bands located to from a cyclone's center migrate outward. They are capable of producing heavy

rains Rains may refer to: Surname *Rains (surname) Places * Rains, South Carolina, an unincorporated community in Marion County, South Carolina * Rains County, Texas, a county in East Texas Entertainment * ''The Rains'', a 2016 zombie novel by Gregg Hu ...

and

squall A squall is a sudden, sharp increase in wind speed lasting minutes, as opposed to a wind gust, which lasts for only seconds. They are usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. Squalls refer to t ...

s of wind, as well as

tornadoes A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, alth ...

, particularly in the storm's right-front quadrant. Some rainbands move closer to the center, forming a secondary, or outer,

eyewall The eye is a region of mostly calm weather at the center of tropical cyclones. The eye of a storm is a roughly circular area, typically in diameter. It is surrounded by the ''eyewall'', a ring of towering thunderstorms where the most severe weat ...

within intense hurricanes. Spiral rainbands are such a basic structure to a tropical cyclone that in most tropical cyclone basins, use of the satellite-based

Dvorak technique The Dvorak technique (developed between 1969 and 1984 by Vernon Dvorak) is a widely used system to estimate tropical cyclone intensity (which includes tropical depression, tropical storm, and hurricane/typhoon/intense tropical cyclone intensities ...

is the primary method used to determine a tropical cyclone's

maximum sustained wind The maximum sustained wind associated with a tropical cyclone is a common indicator of the intensity of the storm. Within a mature tropical cyclone, it is found within the eyewall at a distance defined as the radius of maximum wind, or RMW. U ...

University of Wisconsin–Madison A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. ''University'' is derived from the Latin phrase ''universitas magistrorum et scholarium'', which ...

(1998
Objective Dvorak Technique.
Retrieved on 2006-05-29. Within this method, the extent of spiral banding and difference in temperature between the

and eyewall is used to assign a maximum sustained wind and a central pressure. Central pressure values for their centers of

derived from this technique are approximate. Different programs have been studying these rainbands, including

the Hurricane Rainband and Intensity Change Experiment The Hurricane Rainband and Intensity Change Experiment (RAINEX) is a project to improve hurricane intensity forecasting via measuring interactions between rainbands and the eyewalls of tropical cyclones. The experiment was planned for the 2005 Atla ...

Forced by geography

Convective rainbands can form parallel to terrain on its

windward Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...

side, due to

lee wave In meteorology, lee waves are atmospheric stationary waves. The most common form is mountain waves, which are atmospheric internal gravity waves. These were discovered in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, above ...

s triggered by hills just upstream of the cloud's formation. Their spacing is normally to apart. When bands of precipitation near frontal zones approach steep topography, a low-level barrier jet stream forms parallel to and just prior to the mountain ridge, which slows down the frontal rainband just prior to the mountain barrier. If enough moisture is present,

and land breeze fronts can form convective rainbands. Sea breeze front

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 somet ...

lines can become strong enough to mask the location of an approaching cold front by evening. The edge of

ocean currents An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, ...

can lead to the development of thunderstorm bands due to heat differential at this interface. Downwind of islands, bands of showers and thunderstorms can develop due to low level wind convergence downwind of the island edges. Offshore

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

, this has been noted in the wake of cold fronts.Ivory J. Small (1999)
AN OBSERVATIONAL STUDY OF ISLAND EFFECT BANDS: PRECIPITATION PRODUCERS IN SOUTHERN CALIFORNIA.
Retrieved on 2008-12-26.

References

External links

* * * {{Extratropical cyclones Precipitation Extratropical cyclones Storm Weather hazards Tropical cyclone meteorology Mesoscale meteorology