Subj : Wx Terms (R)(3) To : All From : Daryl Stout Date : Sun Nov 19 2017 12:05 am Red Watch or Red Box Slang for Tornado Watch. REF Reference Reference Mark A relatively permanent point of known elevation which is tied to a benchmark. Reflection The process whereby radiation (or other waves) incident upon a surface is directed back into the medium through which it traveled. Reflectivity Usually a reference to Radar Reflectivity; the sum of all backscattering cross-sections (e.g., precipitation particles) in a pulse resolution volume divided by that volume. The radar reflectivity can be related to the radar reflectivity factor through the dielectric constant term |K|^2, and the radar wavelength. Reflectivity Cross Section This 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 to 124 nm on the horizontal axis. Cross Section is similar to the Range Height Indicator (RHI) slices observed on conventional radar, but it is not limited to alignments along the radar radials. Instead the 2 end points are operator selected anywhere within 124 nm of the radar that are less than 124 nm apart. It is used to: 1) Examine storm structure features such as overhang, tilt, Weak Echo Regions (WER), and Bounded Weak Echo Regions (BWER); 2) Estimate height of higher dBZ's and echo tops; and 3) Locate the bright band (where snow is melting and becoming rain). Reflectivity Factor The result of a mathematical equation (called the Weather Radar Equation) that converts the analog power (in Watts) received by the radar antenna into a more usable quantity. The reflectivity factor (denoted by Z) takes into account several factors, including the distance of a target from the radar, the wavelength of the transmitted radiation, and certain assumptions about the kind and size of targets detected by the radar. The reflectivity factor ranges over several orders of magnitudes, so it is usually expressed on a logarithmic scale called dBZ (decibels of reflectivity). Refraction Changes in the direction of energy propagation as a result of density changes within the propagating medium. In weather terms, this is important on determining how a radar beam reacts in the atmosphere. Refractive Index A 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., n = c / v where: v is actual speed, and c is speed of light in a vacuum. Refractivity Expressed 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 Haze Haze that is mixed uniformly between the surface and the top of a convective boundary layer. Relative Humidity A dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. As such, relative humidity by itself does not directly indicate the actual amount of atmospheric moisture present. See dew point. 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. Relative Wind The wind with reference to a moving point. Sometimes called APPARENT WIND. See also APPARENT WIND, TRUE WIND. RELBL Reliable Relocated A 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 reasonable representation of the cyclone's movement. Remote Observing System Automation A type of automated data transmitter used by NWS Cooperative Program observers. REP Represent/Representative Report A weather report is a statement of the actual weather conditions observed at a specific time at a specific site. Reservoir In hydrologic terms, a manmade facility for the storage, regulation and controlled release of water. Residual Layer The elevated portion of a convective boundary layer that remains after a stable boundary layer develops at the ground (usually in late afternoon or early evening) and cuts off convection. Residual Moisture Atmospheric moisture which lingers over an area after the main weather system has departed. Resonance The 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 is the same, or nearly the same, as the natural vibration frequency of the system. Response Time In hydrologic terms, the 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 closed low or a longwave trough which moves westward. Return Flow South winds on the back (west) side of an eastward-moving surface high pressure system. Return flow over the central and eastern United States typically results in a return of moist air from the Gulf of Mexico (or the Atlantic Ocean). Return Stroke An electrical discharge that propagates upward along a lightning channel from the ground to the cloud. Rex Block A blocking pattern where there is an upper level high located directly north of a closed low. RFC River Forecast Center. Centers that serve groups of Weather Service Forecast offices and Weather Forecast offices, in providing hydrologic guidance and is the first echelon office for the preparation of river and flood forecasts and warnings. RGD Ragged RGN Region RH Relative Humidity - a dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. As such, relative humidity by itself does not directly indicate the actual amount of atmospheric moisture present. See dew point. RHI Range-Height Indicator Ribbon Lightning Appears 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 the strokes are seen at once as a ribbon-like flash. Ridge 1) An elongated area of relatively high atmospheric pressure; the opposite of trough. or 2) In hydrologic terms, a line or wall of broken ice forced up by pressure. May be fresh or weathered. Ridge Ice In hydrologic terms, ice piled haphazardly one piece over another in the form of ridges or walls. Right Ascension The 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 solstice. Right Entrance Region Used interchangably with Right Rear Quadrant; the area upstream from and to the right of an upper-level jet max (as would be viewed looking along the direction of flow). Upward motion and severe thunderstorm potential sometimes are increased in this area relative to the wind speed maximum. See also exit region, left front quadrant. --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .