Subj : Wx Terms (P)(3) To : All From : Daryl Stout Date : Tue Oct 17 2017 12:07 am PNS Public Information Statement - a narrative statement issued by a National Weather Service Forecast Office that can be used for: 1) A current or expected nonhazardous event of general interest to the public that can usually be covered with a single message (e.g., unusual atmospheric phenomena such as sun dogs, halos, rainbows, aurora borealis, lenticular clouds, and stories about a long-term dry/cold/wet/warm spell). 2) Public educational information and activities, such as storm safety rules, awareness activities, storm drills, etc. 3) Information regarding service changes, service limitations, interruptions due to reduced or lost power or equipment outages, or special information clarifying interpretation of NWS data. For example, this product may be used to inform users of radar equipment outages or special information clarifying interpretation of radar data originating from an unusual source which may be mistaken for precipitation (such as chaff drops, smoke plumes, etc., that produces echoes on the radar display. POH Probability of Hail - a product from the NEXRAD hail detection algorithm that estimates the likelihood that hail is present in a storm. Point Precipitation Precipitation at a particular site, in contrast to the mean precipitation over an area. Point Source A pollutant source that can be treated in a dispersion model as though pollutants were emitted from a single point that is fixed in space. Example: the mouth of a smokestack. Compare area source and line source. Polar Cap Absorption (PCA) In solar-terrestrial terms, an anomalous condition of the polar ionosphere whereby HF and VHF (3 - 300 MHz) radiowaves are absorbed, and LF and VLF (3 - 300 kHz) radiowaves are reflected at lower altitudes than normal. In practice, the absorption is inferred from the proton flux at energies greater than 10 MeV, so that PCAs and proton events are simultaneous. Transpolar radio paths may still be disturbed for days, up to weeks, following the end of a proton event. Polar Front A semipermanent, semicontinuous front that separates tropical air masses from polar air masses. Polar Jet Marked by a concentration of isotherms and strong vertical shear, this jet is the boundary between the polar air and the subtropical air. It often divides into two branches, the north and the south, and marks the high speed core of the prevailing westerlies. It is associated with the location and motion of the high and low pressure areas of the middle latitudes, and therefore, is variable in position, elevation, and wind speed. Its position tends to migrate south in the Northern Hemispheric winter and north in the summer, and its core winds increase during the winter and become less strong in the summer. Polar Jet Stream Used interchangably with Polar Jet; a jet stream marked by a concentration of isotherms and strong vertical shear, this jet is the boundary between the polar air and the subtropical air. It often divides into two branches, the north and the south, and marks the high speed core of the prevailing westerlies. It is associated with the location and motion of the high and low pressure areas of the middle latitudes, and therefore, is variable in position, elevation, and wind speed. Its position tends to migrate south in the Northern Hemispheric winter and north in the summer, and its core winds increase during the winter and become less strong in the summer. Polar Orbiting Satellite A weather satellite which travels over both poles each time it orbits the Earth. It orbits about 530 miles (850 km) above the Earth's surface. A satellite with an orbit nearly parallel to the earth's meridian lines which crosses the polar regions on each orbit. Polarization Radar A radar which takes advantage of ways in which the transmitted waves' polarization affect the backscattering. Such radars may alternately transmit horizontal and vertically polarized beams, and measure differential reflectivity. Pollutant Particles, gases, or liquid aerosols in the atmosphere which have an undesirable effect on humans or their surroundings. Something unfavorable to health and life that has been added to the environment. Pondage In hydrologic terms, (1) The holding back of water for later release for power development above the dam of a hydroelectric plant to (a) equalize daily or weekly fluctuations of streamflow or (b) to permit irregular hourly use of water by the wheels to care for fluctuations in the load demand. (2) In general the holding back of water for later releases. (3) The storage capacity available for the use of such water. Ponding In hydrologic terms, in flat areas, runoff collects, or ponds in depression and cannot drain out. Flood waters must infiltrate slowly into the soil, evaporate, or be pumped out. Pool The elevation of the surface of a body of water such as a lake. Specifically, the pool at a lock and dam or a reservoir is the elevation of the water surface immediately upstream from the dam. Pool Height In hydrologic terms, the height of the water behind a dam. (Various datums may be used and various pool height may be used, e.g., conservation pool, flood control pool, etc.). POP Probability of Precipitation Popcorn Convection Slang for showers and thunderstorms that form on a scattered basis with little or no apparent organization, usually during the afternoon in response to diurnal heating. Individual thunderstorms typically are of the type sometimes referred to as air-mass thunderstorms: they are small, short-lived, very rarely severe, and they almost always dissipate near or just after sunset. POPS Probability of Precipitation Porosity In hydrologic terms, (1) The ratio of pore volume to total volume of the formation. Sandy soils have large pores and a higher porosity than clays and other fine-grained soils. (2) An index of the void characteristics of a soil or stream as pertaining to percolation; degree of previousness. POS Positive Positive Area The area on a sounding representing the layer in which a lifted parcel would be warmer than the environment; thus, the area between the environmental temperature profile and the path of the lifted parcel. Positive area is a measure of the energy available for convection; see CAPE. Positive Cloud to Ground Lightning A CG flash that delivers positive charge to the ground, as opposed to the more common negative charge. Positive CGs have been found to occur more frequently in some severe thunderstorms. Their occurrence is detectable by most lightning detection networks, but visually it is not considered possible to distinguish between a positive CG and a negative CG. (Some claim to have observed a relationship between staccato lightning and positive CGs, but this relationship is as yet unproven.) Positive Vorticity Advection (Abbrev. PVA) - Advection of higher values of vorticity into an area, which often is associated with upward motion (lifting) of the air. PVA typically is found in advance of disturbances aloft (i.e., shortwaves), and is a property which often enhances the potential for thunderstorm development. Positive-tilt Trough An upper level system which is tilted to the east with increasing latitude (i.e., from southwest to northeast). A positive-tilt trough often is a sign of a weakening weather system, and generally is less likely to result in severe weather than a negative-tilt trough if all other factors are equal. Post-Flare Loops In solar-terrestrial terms, a loop prominence system often seen after a major two-ribbon flare, which bridges the ribbons. Post-storm Report A report issued by a local National Weather Service office summarizing the impact of a tropical cyclone on it's forecast area. These reports include information on observed winds, pressures, storm surges, rainfall, tornadoes, damage and casualties. Potential Temperature The temperature a parcel of dry air would have if brought adiabatically (i.e., without transfer of heat or mass) to a standard pressure level of 1000 mb. Potential Vorticity This plays an important role in the generation of vorticity in cyclogenesis, especially along the polar front. It is also very useful in tracing intrusions of stratospheric air deep into the troposphere in the vicinity of jet streaks. Powder Snow Dry, loose, unconsolidated snow. --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .