Prognostic DiscussionThis Hydrometeorological Prediction Center (HPC) discussion may include analysis of numerical and statistical models, meteorological circulation patterns…
Progressive DerechoDerecho characterized by a short curved squall line oriented nearly perpendicular to the mean wind direction with a bulge in the general direction of the…
ProminenceA structure in the corona consisting of cool plasma supported by magnetic fields.
propagationThe duplication of a whole plant from a range of vegetative materials; adapted for in vitro culture as micropropagation.
Property ProtectionMeasures that are undertaken usually by property owners in order to prevent, or reduce flood damage.
ProtonA small, positively charged particle of matter found in the atoms of all elements.
Proton EventIn solar-terrestrial terms, the measurement of at least 10 protons/cm2/sec/steradian at energies greater than 10 MeV.
Proton FlareIn solar-terrestrial terms, any flare producing significant fluxes of greater-than-10 MeV protons in the vicinity of the earth.
ProxyIf you own common stock in a US corporation, you have the right to vote on certain company policies and elect the board of directors by casting a proxy…
PSTPlease Send Tell. Indicates that the person speaking wants to receive communication via a /t(ell) or /w(hisper) command.
PsychrometerAn instrument for measuring relative humidity by means of wet and dry-bulb temperatures.
Psychrometric tablesPsychrometric tables Tables prepared from the psychrometric formula and used to obtain vapor pressure, relative humidity, and dew point from wet- and…
PTDYOn a buoy report, Pressure Tendency is the sign (plus or minus) and the amount of pressure change (hPa) for a three hour period ending at the time of…
PTWC(Pacific Tsunami Warning Center) - The Pacific Tsunami Warning Center in Ewa Beach (pronounced Eva Beach), HI has an international warning responsibility…
Public Information StatementA narrative statement issued by a National Weather Service Forecast Office that can be used for: 1) A current or expected nonhazardous event of general…
Public Severe Weather OutlookThese are issued when the Storm Prediction Center (SPC) in Norman, Oklahoma anticipates an especially significant and/or widespread outbreak of severe…
PuddleTo compact loose soil by soaking it and allowing it to dry.
Puget Sound Convergence ZoneA situation where wind forced around the Olympic Mountains converges over the Puget Sound.
PulseA short burst of electromagnetic energy that a radar sends out in a straight line to detect a precipitation target.
Pulse DurationThe time over which a radar pulse lasts. The pulse duration can be multiplied by the speed of light to determine the pulse length or pulse width.
Pulse LengthThe linear distance in range occupied by an individual pulse from a radar. h = c * t , where t is the duration of the transmitted pulse, c is the speed of…
Pulse RadarA type of radar, designed to facilitate range (distance) measurements, in which are transmitted energy emitted in periodic, brief transmission.
Pulse Repetition Frequency (PRF)The amount of time between successive pulses, or bursts, of electromagnetic energy that is transmitted by a radar.
Pulse Repetition Time (PRT)The time elapsed between pulses by the radar. This is also called the pulse interval.
Pulse Resolution VolumeA discrete radar sampling volume, of dimensions (horizontal beamwidth * vertical beamwidth * 1 range gate).
Pulse Severe ThunderstormsSingle cell thunderstorms which produce brief periods of severe weather (3/4 inch hail, wind gusts in the excess of 58 miles an hour, or a tornado).
Pulse StormA thunderstorm within which a brief period (pulse) of strong updraft occurs, during and immediately after which the storm produces a short episode of…
Pulse WidthSame as Pulse Length; the linear distance in range occupied by an individual pulse from a radar.
Pulse-Pair ProcessingNickname for the technique of mean velocity estimation by calculation of the signal complex covariance argument.
PVAThe Plant Variety Act. See U.S. Department of Agriculture.
pWPrecipitable Water - measure of the depth of liquid water at the surface that would result after precipitating all of the water vapor in a vertical column…
PWATPrecipitable Water - measure of the depth of liquid water at the surface that would result after precipitating all of the water vapor in a vertical column…
QPFQuantitative Precipitation Forecast. A spatial and temporal precipitation forecast that will predict the potential amount of future precipitation for a…
QPF DiscussionThis HPC forecast discussion is directed completely to explaining manual forecasts of areas in the contiguous 48 states expected to receive 1/4 inch or…
QuadratureThe component of the complex signal that is 90 degrees out of phase with the inphase component.
Quality Measurement Experiments (QME)(QME)A special class of value-added product that regularly compares two or more data sets intended to understand the individual datastreams either as functions…
Quality of SnowThe amount of ice in a snow sample expressed as a percent of the weight of the sample.
quality-assured dataTypically, the final form of data to be submitted to the ARM data system. Includes datastream description documentation, fully calibrated data in commonly…
Quantitative Precipitation ForecastA spatial and temporal precipitation forecast that will predict the potential amount of future precipitation for a specified region, or area.
Quasi-stationary(abbrev. QSTNRY)- Describes a low or high pressure area or a front that is nearly stationary.
Quasi-stationary FrontA front which is nearly stationary or moves very little since the last synoptic position. Also known as a stationary front.
Quaternary periodthe second period of the Cenozoic era containing the Pleistocene epoch and the Holocene epoch and lasting from 1.8 million years to the present.
Quick LooksDaily and weekly plots of ARM data that give users a browsable quick view of a subset of data available at the ARM Archive.
RADAP IIRAdar DAta Processor II, attached to some WSR-57 and WSR-74 radar units. It automatically controls the tilt sequence and computes several radar-derived…
radarAcronym for RAdio Detection And Ranging; a radio device or system for locating an object by means of ultrahigh-frequency radio waves reflected from the…
Radar BeamThe straight line that a radar pulse travels along. As the radar beam gets further away from the radar, it gets wider and wider.
Radar Coded MessageThis is an alphanumeric coded message which will be used in preparation of a national radar summary chart.
Radar Cross SectionThe area of a fictitious, perfect reflector of electromagnetic waves (e.g., metal sphere) that would reflect the same amount of energy back to the radar…
Radar Data AcquisitionAn acronym for Radar Data Acquisition. The RDA is the hardware component of the NEXRAD system that consists of the radar antenna, transmitter, receiver…
radar dopplerThe power spectrum and moments of the radar signal expressed as a function of Doppler frequency or Doppler velocity.
Radar MeteorologyBranch of meteorology that uses radars for weather observations and forecasts.
Radar MosaicA radar product that combines information from multiple radars to give a regional or national view of reflectivity or precipitation.
Radar Product Generator (RPG)The RPG is the computer in the NEXRAD system that receives polar-coordinate base radar data from the RDA and processes these data into end-user products.
Radar RangeDistance from the radar antenna. The WSR-88D radar has a range for velocity products out to 124 nautical miles and reflectivity products out to 248…
Radar ReflectivityThe sum of all backscattering cross-sections (e.g., precipitation particles) in a pulse resolution volume divided by that volume.
Radar Reflectivity Factor (z)z = the sum (over i) of (N_i * D_i^6), where N_i is the number of drops of diameter D_i in a pulse resolution volume.
Radial VelocityComponent of motion toward or away from a given location. As "seen" by Doppler radar, it is the component of motion parallel to the radar beam.
radianceA measure of the intensity of the radiant energy flux emitted by a body in a given direction.
Radiation(RAY-dee-AY-shun) Energy released in the form of particle or electromagnetic waves.
Radiation FogA fog that forms when outgoing longwave radiation cools the near-surface air below its dew point temperature.
Radiation LawsThe four physical laws which fundamentally describe the behavior of blackbody radiation: Kirchhoff's law, Planck's law, Stefan-Boltzmann law and Wien's…
Radiational CoolingThe cooling of the Earth's surface. At night, the Earth suffers a net heat loss to space due to terrestrial cooling.
Radiational InversionUsed interchangably with Nocturnal Inversion; a temperature inversion that develops during the night as a result of radiational cooling of the surface.
Radiative ForcingRadiative forcing is the change in the net vertical irradiance (expressed in Watts per square metre: Wm-2) at the tropopause due to an internal change or…
radiative heating rateThe heating rate due to the divergence of long and shortwave radiative flux; this is a calculated quantity using the state of the atmospheric and…
Radio EmissionEmissions of the sun in radio wavelengths from centimeters to dekameters, under both quiet and disturbed conditions. Type I.
Radio EventFlares with Centimetric Bursts and/or definite Ionospheric Event (SID)
radiocarbon (<sup>14</sup>C)a radioactive isotope of carbon. Since it decays with a half-life of 5570 years, its concentration in organic materials relative to the stable…