Radioisotope Snow GageA snow water equivalent gage based on the absorption of gamma radiation by snow; this gage can measure up to 55 inches water equivalent with a 2 to 5…
RadiosondeAn instrument that is carried aloft by a balloon to send back information on atmospheric temperature, pressure and humidity by means of a small…
Radius of Maximum WindsThe distance from the center of a tropical cyclone to the location of the cyclone's maximum winds.
RainPrecipitation that falls to earth in drops more than 0.5 mm in diameter.
Rain FootSlang for a horizontal bulging near the surface in a precipitation shaft, forming a foot-shaped prominence. It is a visual indication of a wet microburst.
Rain ForestA forest which grows in a region of heavy annual precipitation. There are two major types, tropical and temperate.
rain gageA device, usually a cylindrical container, for measuring rainfall.
Rain GaugeAn instrument for measuring the quantity of rain that has fallen.
Rain Induced FogWhen warm rain falls through cooler air, water evaporates from the warm rain. It subsequently condenses in the cool air forming fog.
Rain ShadowAn area of reduced precipitation on the lee side of a mountain barrier caused by warming of air and dissipation of cloudiness as air descends the barrier.
Rain ShieldIn a hurricane, a solid or nearly solid area of rain that typically becomes heavier as one approaches the eye.
Rain-free BaseA dark, horizontal cloud base with no visible precipitation beneath it. It typically marks the location of the thunderstorm updraft.
RainbowA flop that contains three different suits, thus no flush can be made on the turn.
RainfallThe amount of precipitation of any type, primarily liquid. It is usually the amount that is measured by a rain gauge.
Rainfall EstimatesA series of NEXRAD products that employ a Z-R relationship to produce accumulations of surface rainfall from observed reflectivity.
RangeGeographic region in which a given plant or animal normally lives or grows.
Range FoldingThis occurs when the radar receives a signal return from a pulse other than the most recent pulse.
Range GateThe discrete point in range along a single radial of radar data at which the received signal is sampled.
Range Height IndicatorThe RHI is a radar display in which the radar scans vertically, with the antenna pointing at a specific azimuth or radial.
Range NormalizationA receiver gain function in the radar which compensates for the effect of range (distance) on the received power for an equivalent reflectivity.
Range ResolutionThe ability of the radar to distinguish two targets along the same radial but at different ranges. it is approximately ½ the pulse length.
Range UnfoldingProcess of removing range ambiguity in apparent range of a multitrip target on the radar.
RangelandLand on which the native vegetation, climax, or natural potential consists predominately of grasses, grasslike plants, forbs, or shrubs.
Rankine VortexVelocity profile for a symmetric circulation in which the inner core is in solid rotation and tangential winds outside the core vary inversely with radial…
Rapid DeepeningA decrease in the minimum sea-level pressure of a tropical cyclone of 1.75 mb/hr or 42 mb for 24 hours
Rapid IntensificationAn increase in the maximum sustained winds of a tropical cyclone of at least 30 kt in a 24-h period.
Rapidly IntensifyingIndicator for a maritime cyclone whose central pressure is dropping, or is expected to drop, at a rate of 1 MB per hour for 24 hours.
RawinsondeA radiosonde that is tracked to measure winds.
ReachAny specified length of stream, channel, or other water conveyance. A portion of a stream or a river.
Real TimeWhen an event is reported as it happens - such as a quick jump in a stock's price or the constantly changing numbers on a market index - you are getting…
Rear Flank DowndraftA region of dry air subsiding on the back side of, and wrapping around, a mesocyclone. It often is visible as a clear slot wrapping around the wall cloud.
ReceiverThe component of a central receiver solar thermal system where reflected solar energy is absorbed and converted to thermal energy.
Reconnaissance CodeAn aircraft weather reconnaissance code that has come to refer primarily to in-flight tropical weather observations, but actually signifies any detailed…
Record Event ReportThis non-routine narrative product is issued by the National Weather Service to report meteorological and hydrological events that equal or exceed…
Recreation ReportThis National Weather Service product is used to relay reports on conditions for resorts and recreational areas and/or events.
recurrence(ree-KER-ents) Cancer that has recurred (come back), usually after a period of time during which the cancer could not be detected.
RecyclingThe process of converting materials that are no longer useful as designed or intended into a new product.
Red FlagThis a fire weather program which highlights the onset of critical weather conditions conducive to extensive wildfire occurrences.
Red Flag WarningA term used by fire-weather forecasters to call attention to limited weather conditions of particular importance that may result in extreme burning…
Reference MarkA relatively permanent point of known elevation which is tied to a benchmark.
reflectionThe process whereby radiation (or other waves) incident upon a surface is directed back into the medium through which it traveled.
ReflectivityThe measure of the efficiency of a radar target in intercepting and returning Electro Magnetic Energy.
reflectivity (dBZ)(dBZ)A measure of the returned power, which is sensitive to the size and number of hydrometeors (i.e., the particle size spectra).
Reflectivity Cross SectionThis WSR-88D radar product displays a vertical cross section of reflectivity on a grid with heights up to 70,000 feet on the vertical axis and distance up…
Reflectivity FactorThe result of a mathematical equation (called the Weather Radar Equation) that converts the analog power (in Watts) received by the radar antenna into a…
ReforestationPlanting of forests on lands that have previously contained forests but that have been converted to some other use.
RefractionThe change in direction of a ray of light when it passes through one media to another with differing optical densities.
Refractive IndexA measure of the amount of refraction. Numerically equal to the ratio of wave velocity in a vacuum to a wave speed in the medium, i.e.
RefractivityExpressed as N; N = (n-1)*106, where n is refractive index and N is a function of temperature, pressure and vapor pressure (in the atmosphere).
Regional HazeHaze that is mixed uniformly between the surface and the top of a convective boundary layer.
relative datingthe process of determining the order in which certain events occurred or certain materials were formed.
Relative HumidityA measure of the percent of moisture actually in the air compared with what would be in it if it were fully saturated at that temperature.
Relative VorticityThe 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.
Relative WindThe wind with reference to a moving point. Sometimes called APPARENT WIND. See also APPARENT WIND, TRUE WIND.
RelocatedA term used in an advisory to indicate that a vector drawn from the preceding advisory position to the latest known position is not necessarily a…
Remnant LowA post-tropical cyclone that no longer possesses the convective organization required of a tropical cyclone...
ReportFormatted output of a system providing specific information.
ReservoirA reservoir of an infectious agent, such as a virus, is any animal, person, plant, soil, substance—or combination of any of these — in which the…
Residence TimeThe average time spent in a reservoir by an individual atom or molecule. With respect to greenhouse gases, residence time usually refers to how long a…
Residual fuel oilHeavy fuel oil produced from the residue in the fractional distillation process rather than from the distilled fractions. No.
Residual Layerthe elevated portion of a convective boundary layer that remains after a stable boundary layer develops at the ground (usually in late afternoon or early…
Residual MoistureAtmospheric moisture which lingers over an area after the main weather system has departed.
resonanceThe state of a system in which an abnormally large vibration is produced in response to an external stimulus, occurring when the frequency of the stimulus…
RespirationThe process whereby living organisms convert organic matter to CO2, releasing energy and consuming O2.
Response TimeThe amount of time in which it will take a watershed to react to a given rainfall event.
Retrogression(or Retrograde Motion) - Movement of a weather system in a direction opposite to that of the basic flow in which it is embedded, usually referring to a…
Return FlowDrainage water from irrigated farmlands that re-enters the water system to be used further downstream.
Return StrokeAn electrical discharge that propagates upward along a lightning channel from the ground to the cloud.
Rex BlockA blocking pattern where there is an upper level high located directly north of a closed low.
RFCRiver Forecast Center. Centers that serve groups of Weather Service Forecast offices and Weather Forecast offices, in providing hydrologic guidance and is…
Ribbon LightningAppears to be a broad stream of fire. A succession of strokes, each blown a bit to the side of the previous strokes by wind, but striking so fast that all…
RidgeA line or wall of broken ice forced up by pressure. May be fresh or weathered.
Ridge IceIce piled haphazardly one piece over another in the form of ridges or walls.
Right AscensionThe celestial longitude of the sun. This value is 0 at the vernal equinox, 90 at the summer solstice, 180 at the autumnal equinox and 270 at the winter…