Subj : Wx Terms (P)(5) To : All From : Daryl Stout Date : Thu Aug 17 2017 12:04 am Pressure Rising Rapidly An increase in station pressure at a rate of 0.06 inch of mercury or more per hour which totals 0.02 inch or more. Pressure Tendency The character and amount of atmospheric pressure change during a specified period of time, usually 3-hour period preceding an observation. Pressure Unsteady A pressure that fluctuates by 0.03 inch of mercury or more from the mean pressure during the period of measurement. Pressure-driven Channeling Channeling of wind in a valley by synoptic-scale pressure gradients superimposed along the valley's axis. Compare forced channeling. Prevailing Visibility The visibility that is considered representative of conditions at the station; the greatest distance that can be seen throughout at least half the horizon circle, not necessarily continuous. Prevailing Westerlies The westerly winds that dominant in middle latitudes. Prevailing Winds A wind that consistently blows from one direction more than from any other. Prevention of Significant Deterioration A program, specified in the Clean Air Act, whose goal is to prevent air quality from deteriorating significantly in areas of the country that are presently meeting the ambient air quality standards. PRIM Primary Primary Ambient Air Quality Standards Air quality standards designed to protect human health. Primary Control Tide Station A tide station where continuous observations have been made for a minimum of 19 years. Its purpose is to provide data for computing accepted values essential to tide predictions and for determining tidal datums for coastal and marine boundaries. The data series from primary control tide stations serves as a primary control for the reduction of tidal datum for subordinate tide stations with a shorter period of record. The 19 year period is the official tidal epoch for calculating tidal datums. Primary Pollutant Substances that are pollutants immediately on entering the atmosphere. Compare secondary pollutant. Primary Swell Direction Prevailing direction of swell propagation. PRIN Principal Probability A chance, or likelihood, that a certain event might happen. Probability Forecast A forecast of the probability that one or more of a mutually exclusive set of weather conditions will occur. Probability of Hail (Abbrev. POH) - a product from the NEXRAD hail detection algorithm that estimates the likelihood that hail is present in a storm. Probability of Precipitation (Abbrev. PoP)- The probability that precipitation will be reported at a certain location during a specified period of time. Probability of Thunderstorms The probability based on climatology that a thunderstorm will be reported at that location during a specified period of time. Probability of Tropical Cyclone Conditions The probability, in percent, that the cyclone center will pass within 50 miles to the right or 75 miles to the left of the listed location within the indicated time period when looking at the coast in the direction of the cyclone's movement. Product Resolution The smallest spatial increment or data element that is distinguishable in a given Doppler radar product. Profiler An instrument designed to measure horizontal winds directly above its location, and thus measure the vertical wind profile. Profilers operate on the same principles as Doppler radar. PROG Forecast (prognostication) PROGGED Forecasted Prognostic Discussion This Hydrometeorological Prediction Center (HPC) discussion may include analysis of numerical and statistical models, meteorological circulation patterns and trends, and confidence factors. Reference is usually made to the manually produced 6 to 10-day Northern Hemisphere prognoses for mean 500 millibar heights and mean 500 millibar height anomalies. Discussions may also refer to the method of operational ensemble predictions. Progressive Derecho Derecho characterized by a short curved squall line oriented nearly perpendicular to the mean wind direction with a bulge in the general direction of the mean flow. Downburst activity occurs along the bulging portion of the line. This type of derecho typically occurs in the warm season (May through August) and is most frequent in a zone extending from eastern South Dakota to the upper Ohio Valley. The severe wind storms typically begin during the afternoon and continue into the evening hours. Several hours typically pass between initial convection and the first wind damage report. Prominence A term identifying cloud-like features in the solar atmosphere. The features appear as bright structures in the CORONA above the solar LIMB and as dark FILAMENTs when seen projected against the solar DISK. PROPA Propagation (movement) Propagation 1. The movement of an atmospheric phenomenon. This term is frequently applied to the motion of thunderstorms into regions favorable for their continued development (into a maritime tropical airmass). 2. The transmission of electromagnetic energy as waves through or along a medium. Property Protection Measures that are undertaken usually by property owners in order to prevent, or reduce flood damage. Property protection measures are often inexpensive for the community because they are implemented by or cost-shared with property owners. In many cases the buildings' appearance or use is unaffected, so these measurements are particularly appropriate for historical sites and landmarks. These measures include relocation and acquisition, flood proofing, and buying flood insurance. Proton Solar activity levels with at least one high energy event (Class X Flares). Proton Event In solar-terrestrial terms, the measurement of at least 10 protons/cm2/sec/steradian at energies greater than 10 MeV. Proton Flare In solar-terrestrial terms, any flare producing significant fluxes of greater-than-10 MeV protons in the vicinity of the earth. PRST Persist PRVD Provide PSBL Possible PSBLY possibly Pseudo-Cold Front A boundary between a supercell's inflow region and the rear-flank downdraft (or RFD). It extends outward from the mesocyclone center, usually toward the south or southwest (but occasionally bows outward to the east or southeast in the case of an occluded mesocyclone), and is characterized by advancing of the downdraft air toward the inflow region. It is a particular form of gust front. Pseudo-Warm Front A boundary between a supercell's inflow region and the forward-flank downdraft (or FFD). It extends outward from at or near the mesocyclone center, usually toward the east or southeast, and normally is either nearly stationary or moves northward or northeastward ahead of the mesocyclone. PSG Passage PST Pacific Standard Time Psychrometer An instrument used to measure the water vapor content of the air; a hygrometer consisting essentially of two similar thermometers with the bulb of one being kept wet so that the cooling that results from evaporation makes it register a lower temperature than the dry one and with the difference between the readings constituting a measure of the dryness of the atmosphere. --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .