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WeatherChannel - Weather Terms Category: Meteorology and astronomy > Weather Glossary Date & country: 30/09/2008, USA Words: 751

range resolution
The ability of radar to distinguish between targets on the same azimuth but at different ranges.

rawinsonde
An upper air observation that evaluates the winds, temperature, relative humidity, and pressure aloft by means of a balloon-attached radiosonde that is tracked by a radar or radio direction-finder. It is a radiosonde observation combined with a winds-aloft observation, called a rawin.

reconnaissance (recco) code
An aircraft weather reconnaissance code that has come to refer primarily to in-flight tropical weather observations, but actually signifies any detailed weather observation or investigation from an aircraft in flight.

reflectivity
A measure of the process by which a surface can turn back a portion of incident radiation into the medium through which the radiation approached. It also refers to the degree by which precipitation is able to reflect a radar beam. Related term: albedo

refraction
The bending of light or radar beam as it passes through a zone of contrasting properties, such as atmospheric density, water vapor, or temperature.

relative humidity
A type of humidity that considers the ratio of the actual vapor pressure of the air to the saturation vapor pressure. It is usually expressed in percentage.

relative vorticity
The sum of the rotation of an air parcel about the axis of the pressure system and the rotation of the parcel about its own axis. Related term: vorticity

resolution
In relation to radar, it is the ability to read two distinct targets separately. The clearer the resolution, the nearer the two objects can be to each other and still be distinguishable.

retrogression
In meteorology, it is the movement of a weather system in a direction opposite to the direction of the basic flow in which it is embedded. Often used in reference to a long wave trough or other macroscale feature. For example, a long wave trough that may move slightly westward when the 'normal' movement and flow is eastward.

ridge
An elongated area of high atmospheric pressure that is associated with an area of maximum anticyclonic circulation. The opposite of a trough.

rime
The rapid freezing of supercooled water droplets as they touch an exposed object, forming a white opaque granular deposit of ice. It is one of the results of an ice storm, and when formed on aircraft it is called rime icing. Related term: glaze

rip current
It is formed by a strong surface water movement, or current, of a short duration that flows seaward from the shore. The return flow is piled up onshore by the incoming waves and wind. It is localized, of narrow width, and its position relative to the beach can change as the wave condition changes. Therefore, the higher the waves, the stronger the c...

rocketsonde
A type of radiosonde that is shot into the atmosphere by a rocket, allowing it to collect data during its parachute descent from a higher position in the atmosphere than a balloon could reach.

roll cloud
A relatively rare, low-level, horizontal, tube-shaped cloud. Although they are associated with a thunderstorm, they are completely detached from the base of the cumulonimbus cloud.

rossby waves
The movement of ridges and troughs in the upper wind patterns, primarily the jet stream, circling the earth. Named for Carl-Gustaf Rossby, a U.S. Weather Bureau (NWS) employee, who first theorized about the existence of the jet stream in 1939.

rotation
The spinning of a body, such as the earth, about its axis.

rotor cloud
An altocumulus cloud formation that can be found in the lee of a mountain or similar barrier. The air rotates around a horizontal axis, creating turbulence. Altocumulus lenticularis is an example.

salinity
A measure of the quantity of dissolved salts in sea water. The total amount of dissolved solids in sea water in parts per thousand by weight.

salt water
The water of the ocean, distinguished from fresh water by its appreciable salinity.

sand
Loose particles of hard, broken rock or minerals. In observing, sand is reported when particles of sand are raised to sufficient height that reduces visibility. It is reported as 'SA' in an observation and on the METAR.

sandstorm
A strong wind carrying sand particles through the air. They are low level occurences, usually only ten feet in height to not more than fifty feet above the surface. Due to the frequent winds created by surface heating, they are most predominate during the day and die out in the night. Visibility is reduced to between 5/8ths and 6/16ths statute mile...

santa ana winds
The hot, dry winds, generally from the east, that funnel through the Santa Ana river valley south of the San Gabriel and San Bernadino Mountains in southern California, including the Los Angeles basin. Classified as katabatic, it occurs most often during the winter and it is an example of a foehn wind.

sargasso sea
An area of the North Atlantic Ocean between Bermuda and the Azores. It is in the middle of the North Atlantic oceanic gyre, with converging surface waters. Consequently, it has less biological features than any other region of the ocean because the lack of mixing with more nutrient-rich waters.

satellite
Any object that orbits a celestial body, such as a moon. However, the term is often used in reference to the manufactured objects that orbit the earth, either in a geostationary or a polar manner. Some of the information that is gathered by weather satellites, such as GOES9, includes upper air temperatures and humidity, recording the temperatures o...

satellite images
Images taken by a weather satellite that reveal information, such as the flow of water vapor, the movement of frontal system, and the development of a tropical system. Looping individual images aids meteorologists in forecasting. One way a picture can be taken is as a visible shot, that is best during times of visible light (daylight). Another way ...

saturate
To treat or charge something to the point where no more can be absorbed, dissolved, or retained. In meteorology, it is used when discussing the amount of water vapor in a volume of air.

saturation point
The point when the water vapor in the atmosphere is at its maximum level for the existing temperature.

scattered
The amount of sky cover for a cloud layer between 3/8ths and 4/8ths, based on the summation layer amount for that layer.

scattering
The process by which small particles suspended in the air diffuse a portion of the incident radiation in all directions. This is a primary reason for colors, such as blue skies, rainbows, and orange sunsets. When working with radars, this often refers to the more or less random changes in direction of radio energy.

scud
Low fragments of clouds, usually stratus fractus, that are unattached and below a layer of higher clouds, either nimbostratus or cumulonimbus. They are often along and behind cold fronts and gust fronts, being associated with cool moist air, such as an outflow from a thunderstorm. When observed from a distance, they are sometimes mistaken for torna...

sea breeze
A diurnal coastal breeze that blows onshore, from the sea to the land. It is caused by the temperature difference when the surface of the land is warmer than the adjacent body of water. Predominate during the day, it reaches its maximum early to mid afternoon. It blows in the opposite direction of a land breeze.

sea breeze front
A coastal phenomena, it is restricted to large bodies of water and their immediate coast lines. This is usually the landward extent of the sea breeze. Due to the imbalance of heating between land and water, a region of maximum upward motion or convergence occurs by mid-afternoon in the summer some 10 to 15 miles inland. Air mass thunderstorms or a ...

sea fog
A type of advection fog which forms in warm moist air cooled to saturation as the air moves across cold water. Related term: Arctic Sea Smoke

sea ice
Ice that is formed by the freezing of sea water. It forms first as small crystals, thickens into sludge, and coagulates into sheet ice, pancake ice, or ice floes of various shapes and sizes.

sea level
The height or level of the sea surface at any time. It is used as a reference for elevations above and below. Related term: mean sea level

sea level pressure
The atmospheric pressure at mean sea level, usually determined from the observed station pressure.

sea mile
A unit of length distinguished from a nautical mile. One sea mile is equivalent to 1,000 fathoms (6,000 feet).

season
A division of the year according to some regularly recurring phenomena, usually astronomical or climatic. For example, in the Northern Hemisphere, winter is said to begin on the winter solstice and end on the vernal equinox when spring begins, covering the months of December, January, and February. In the tropics, there is the dry and the rainy sea...

sea spray
Sometimes called salt spray, it is the drops of sea water (salt water) blown from the top of a wave. Related terms: blowing spray and condensation nuclei

sea surface temperature (sst)
The temperature of the water's surface. It is measured using buoy and ship data, infrared satellite imagery, and coastal observations.

semi-permanent pressure systems
A relatively stable, stationary pressure-and-wind system where the pressure is predominately high or low with the changing season. They are not of a transitory nature, like migratory lows that develop from temperature and density differences. Related terms: Icelandic Low, Aleutian Low, North Pacific High, Siberian High, and Bermuda High

severe weather
Generally, any destructive weather event, but usually applies to localized storms, such as blizzards, intense thunderstorms, or tornadoes.

severe thunderstorm
A thunderstorm with winds measuring 50 knots (58 mph) or greater, 3/4 inch hail or larger, or tornadoes. Severe thunderstorms may also produce torrential rain and frequent lightning. Related term: supercell

shear
It is the rate of change over a short duration. In wind shear, it can refer to the frequent change in wind speed within a short distance. It can occur vertically or horizontally. Directional shear is a frequent change in direction within a short distance, which can also occur vertically or horizontally. When used in reference to Doppler radar, it d...

shear line
A line of maximum horizontal wind shear. A narrow zone across which there is an abrupt change in the horizontal wind component parallel to it.

short wave
A progressive wave of smaller amplitude, wave length, and duration than a long wave. It moves in the same direction as the basic current in which it is embedded and may induce upward vertical motion ahead of it. They are more numerous than long waves and often disappear with height in the atmosphere.

showalter stability index
A measure of the local static stability of the atmosphere. It is determined by lifting an air parcel to 500 millibars and then comparing its temperature to that of the environment. If the parcel is colder than its new environment, then the atmosphere is more stable. If the parcel is warmer than its new environment, then the atmosphere is unstable a...

shower
Precipitation from a convective cloud that is characterized by its sudden beginning and ending, changes in intensity, and rapid changes in the appearance of the sky. It occurs in the form of rain (SHRA), snow (SHSN), or ice (SHPE). It is reported as 'SH' in an observation and on the METAR.

siberian express
A fierce, cold flow of air that originates in Siberia, then moves into Alaska and northern Canada before moving southward into the United States.

siberian high
The semi-permanent high pressure area that forms over Siberia during the winter. The average central pressure exceeds 1030 millibars from late November to early March. It is characterized by clear, dry weather. Over southern Asia, the predominate surface wind is northeasterly, just the opposite of the predominate summer winds which bring the monsoo...

sidereal time
The measure of time as defined by the diurnal motion of the vernal equinox. A sidereal day is equivalent to one complete rotation of the earth relative to the equinox, which is 23 hours, 56 minutes, and 4.091 seconds. A sidereal year is the interval required for the earth to make one absolute revolution around the sun, which is 365 days, 6 hours, 9...

skew t-log p diagram
A thermodynamic diagram, using the temperature and the logarithm of pressure as coordinates. It is used to evaluate and forecast air parcel properties. Some values that can be determined are the Convective Condensation Level (CCL), the Lifting Condensation Level (LCL), and the Level of Free Convection (LFC).

sky
The vault-like apparent surface against which all aerial objects are seen from the earth.

sky cover
The amount of the celestial dome that is hidden by clouds and/or obscurations.

sleet
Also known as ice pellets, it is winter precipitation in the form of small bits or pellets of ice that rebound after striking the ground or any other hard surface. It is reported as 'PE' in an observation and on the METAR.

slush
Snow or ice on the ground that has been reduced to a softy watery mixture by rain and/or warm temperatures.

small craft advisory
An advisory issued for marine interests, especially for operators of small boats or other vessels. Conditions include wind speeds between 20 knots (23 mph) and 34 knots (39 mph).

smoke
Small particles produced by combustion that are suspended in the air. A transition to haze may occur when the smoke particles have traveled great distance (25 to 100 miles or more), and when the larger particles have settled out. The remaining particles become widely scattered through the atmosphere. It is reported as 'FU' in an observation and on ...

snow
Frozen precipitation in the form of white or translucent ice crystals in complex branched hexagonal form. It most often falls from stratiform clouds, but can fall as snow showers from cumuliform ones. It usually appears clustered into snowflakes. It is reported as 'SN' in an observation and on the METAR.

snow advisory
A statement or advisory issued when snow is expected to create hazardous travel conditions. It warns of less severe weather conditions than a winter storm

snow banner
A plume of snow blown off a mountain crest, resembling smoke blowing from a volcano.

snow blindness
Temporary blindness or impaired vision that results from bright sunlight reflected off the snow surface. The medical term is niphablepsia.

snowburn
A burn of the skin, like a sunburn, but caused by the sun's rays reflected off the snow surface.

snow cover
The areal extent of ground covered by the snow. It is usually expressed as a percent of the total area of a given region.

snow creep
A continuous, extremely slow, downhill movement of a layer of snow.

snow crust
The crisp, almost icy, surface on fallen snow, usually formed by the slight melting and refreezing of the surface snow.

snow depth
The actual depth of snow on the ground at any instant during a storm, or after any single snowstorm or series of storms.

snow devil
A small, rotating wind that picks up loose snow instead of dirt (like a dust devil) or water (like a waterspout). Formed mechanically by the convergence of local air currents. May be called a snowspout.

snow eater
Any warm downslope wind, or foehn, that blows over snowy terrain and melts the snow. Related term: Chinook and Dave's Dictionary

snowfall
The rate at which snow falls, usually expressed in inches of snow depth over a six hour period.

snowflakes
An ice crystal or an aggregate of ice crystals which fall from clouds.

snow flurry/flurries
Light showers of snow, generally very brief without any measurable accumulation. May be reported as 'SHSN--' in an observation and on the METAR.

snow garland
Snow appearing as a beautiful long thick rope draped on trees, fences and other objects. Formed by the surface tension of thin films of water bonding individual snow crystals.

snow grains
Frozen precipitation in the form of very small, white, opaque grains of ice. The solid equivalent of drizzle. It is reported as 'SG' in an observation and on the METAR.

snow level
The elevation in mountainous terrain where the precipitation changes from rain to snow, depending on the temperature structure of the associated air mass.

snow line
The lowest elevation area of a perennial snow field on high terrain, such as a mountain range.

snowpack
The amount of annual accumulation of snow at higher elevations.

snow pellets
Frozen precipitation in the form of white, round or conical opaque grains of ice. Their diameter ranges from 0.08 to 0.2 inch (2 to 5 mm). They are easily crushed and generally break up after rebounding from a hard surface, unlike hail. Sometimes it is called small or soft hail. It is reported as 'GS' in an observation and on the METAR.

snow roller
The product of moist, cohesive snow that when initiated by wind rolls across the landscape, gathering snow until it can no longer move. It is shaped like a rolled sleeping bag, some reaching four feet across and seven feet in diameter.

snow shower
Frozen precipitation in the form of snow, characterized by its sudden beginning and ending. It is reported as 'SHSN' in an observation and on the METAR.

snow squall
A heavy snow shower accompanied by sudden strong winds, or a squall.

solar day
The complete rotation of the earth in relation to the sun. Although it varies, an average has determined a mean solar day of 24 hours. It is universally used for civil purposes. Related term: sidereal day

solar eclipse
An eclipse of the sun occurs when the moon is in a direct line between the sun and the earth, casting some of the earth's surface in its shadow. The moon's disk shaped outline appears to cover the sun's brighter surface, or photosphere. That part of the earth that is directly in the moon's shadow will see a total eclipse of the sun, while the areas...

solstice
The point at which the sun is the furthest on the ecliptic from the celestial equator. The point at which sun is at maximum distance from the equator and days and nights are most unequal in duration. The Tropic of Cancer and the Tropic of Capricorn are those parallels of latitude which lies directly beneath a solstice. In the Northern Hemisphere, t...

sounding
A plot of the atmosphere, using data rom upper air or radiosonde observations. Usually confined to a vertical profile of the temperatures, dew points, and winds above a fixed location.

southern oscillation
A periodic reversal of the pressure pattern across the tropical Pacific Ocean during El NiÑo events. It is represents the distribution of temperature and pressure over an oceanic area.

specific humidity
The ratio of the density of the water vapor to the density of the air, a mix of dry air and water vapor. It is expressed in grams per gram or in grams per kilograms. The specific humidity of an air parcel remains constant unless water vapor is added to or taken from the parcel.

spring
The season of the year which occurs as the sun approaches the summer solstice, and characterized by increasing temperatures in the mid-latitudes. Customarily, this refers to the months of March, April, and May in the North Hemisphere, and the months of September, October, and November in the Southern Hemisphere. Astronomically, this is the period b...

spring tide
A tide of increased range, which occurs about every two weeks when the moon is new or full. Related term: neap tide

squall
A sudden onset of strong winds with speeds increasing to at least 16 knots (18 miles per hour) and sustained at 22 or more knots (25 miles per hour) for at least one minute. The intensity and duration is longer than that of a gust. It is reported as 'SQ's in an observation and on the METAR.

squall line
A narrow band or line of active thunderstorms that is not associated with a cold front. It may form from an outflow boundary or the leading edge of a mesohigh.

st. elmo's fire
A luminous, and often audible, electric discharge that is sporadic in nature. It occurs from objects, especially pointed ones, when the electrical field strength near their surfaces attains a value near 1000 volts per centimeter. It often occurs during stormy weather and might be seen on a ship's mast or yardarm, aircraft, lightning rods, and steep...

stable/stability
Occurs when a rising air parcel becomes denser than the surrounding air. It will then return to its original position. When the density of the air parcel remains the same as the surrounding air after being lifted, it is also considered stable, since it does not have the tendency to rise or sink further. Contrast with unstable air and instability.

stagnation area
An area that has a combination of stable stratification, weak horizontal wind speed, and little, if any, significant precipitation. It is usually associated with an area of high pressure. Related terms: Tule fog

standard atmosphere
A standard atmosphere has been defined by the International Civil Aeronautical Organization (ICAO). It assumes a mean sea level temperature of 15°C a standard sea level pressure of 1,013.25 millibars or 29.92 inches of mercury, and a temperature lapse rate of 0.65°C per 100 meters up to 11 kilometers in the atmosphere.

standard surface pressure
The measurement of one atmosphere of pressure under standard conditions. It is equivalent to 1,013.25 millibars, 29.92 inches of mercury, 760 millimeters of mercury, 14.7 pounds per square inch, or 1.033 grams per square centimeter.

standing cloud
Any type of isolated cloud, generally formed over peaks or ridges of mountainous areas, that appears stationary or standing over the terrain. Related term: altocumulus lenticularis

standing wave
An atmospheric wave that is stationary with respect to the medium in which it is embedded. Related term: mountain wave

stationary front
A front which is nearly stationary or moves very little since the last synoptic position. May be known as a quasi-stationary front.

station elevation
The vertical distance above mean sea level that is the reference level for all current measurements of atmospheric pressure at that station.