Subj : Wx Terms (P)(2) To : All From : Daryl Stout Date : Mon Jul 17 2017 12:08 am Perennial Stream In hydrologic terms, a stream that flows all year round. Perigee The closest distance between moon and earth or the earth and sun. Perihelion The point on the annual orbit of a body (about the sun) that is closest to the sun; at present, the earth reaches this point on about 5 January. Opposite of aphelion. Permafrost A layer of soil at varying depths below the surface in which the temperature has remained below freezing continuously from a few to several thousands of years. Permeability In hydrologic terms, the ability of a material to transmit fluid through its pores when subjected to a difference in head. Permeability Coefficient In hydrologic terms, the rate of flow of a fluid through a cross section of a porous mass under a unit hydraulic gradient, at a temperature of 60 degrees Fahrenheit. Permeameter In hydrologic terms, a laboratory instrument for determining permeability by measuring the discharge through a sample of the material when a known hydraulic head is applied. Persistence Continuation of existing conditions. When a physical parameter varies slowly, the best prediction is often persistence. Persistence Forecast A forecast that the current weather condition will persist and that future weather will be the same as the present (e.g., if it is raining today, a forecast predicting rain tonight). Perturbation Model A computer model used to calculate air pollution concentrations. A perturbation model produces a wind field from solutions to a simplified set of equations that describe atmospheric motions. Pervious Zone In hydrologic terms, a part of the cross section of an embankment dam comprising material of high permeability. PFD QPF Discussion (issued by the HPC) Phenomenological Model A computer model used to calculate air pollution concentrations. A phenomenological model focuses on an individual phenomenon, such as plume impingement or fumigation. Phiezometer In hydrologic terms, an instrument used to measure pressure head in a conduit, tank, soil, etc. They are used in dams to measure the level of saturation. Photochemical Smog Air pollution containing ozone and other reactive chemical compounds formed by the reaction of nitrogen oxides and hydrocarbons in the presence of sunlight. Photosphere The intensely bright portion of the sun visible to the unaided eye; the "surface" of the sun. Reaching temperatures estimated at about 11,000 degrees Fahrenheit, it is the portion of the sun's atmosphere which emits continuous electromagnetic radiation. Phreatic water In hydrologic terms, water within the earth that supplies wells and springs; water in the zone of saturation where all openings in rocks and soil are filled, the upper surface of which forms the water table. Also termed Groundwater. PIBAL Pilot balloon. A small helium-filled meteorological balloon that is tracked as it rises through the atmosphere to determine how wind speed and direction change with altitude. Pilot Balloon (Abbrev. PIBAL)- A small helium-filled meteorological balloon that is tracked as it rises through the atmosphere to determine how wind speed and direction change with altitude. Pilot Report (Abbrev. PIREP)- A report of inflight weather by an aircraft pilot or crew member. A complete coded report includes the following information in this order: location and/or extent of reported weather phenomenon: type of aircraft (only with reports turbulence or icing). Pingo A large frost mound of more than one-year duration. PIREP Pilot Report. A report of inflight weather by an aircraft pilot or crew member. A complete coded report includes the following information in this order: location and/or extent of reported weather phenomenon: type of aircraft (only with reports turbulence or icing). Pitot Tube In hydrologic terms, a device for measuring the velocity of flowing water using the velocity head of the stream as an index of velocity. It consists essentially of an orifice held to a point upstream in the water, connected with a tube in which the rise of water due to velocity head may be observed and measured. It also may be constructed with an upstream and downstream orifice, with two water columns, in which case the difference in height of water column in the tubes is the index of velocity. PIX picture PK Peak PL Ice pellets (sleet) Plage In solar-terrestrial terms, an extended emission feature of an active region that exists from the emergence of the first magnetic flux until the widely scattered remnant magnetic fields merge with the background. Plage Corridor In solar-terrestrial terms, a space in chromospheric plage lacking plage intensity, coinciding with polarity inversion line. Plagenil In solar-terrestrial terms, spotless disc free of calcium plage. Plan Position Indicator An acronym for Plan Position Indicator. A PPI displays radar data horizontally using a map projection. In PPI mode, the radar makes a 360-degree sweep with the antenna at a specific elevation angle. A PPI display is the familiar radar display shown on the television weather programs. Planetary Boundary Layer The layer within the atmosphere between 1 km and the earth's surface where friction affects wind speed and wind direction. Plasma Any ionized gas; that is, any gas containing ions and electrons. Platform A generic radar term, often used to encompass the pedestal and antenna assembly; sometimes including the radar control, display and analysis hardware and software as well. Plow Wind A term used in the midwestern United States to describe strong, straight-line winds associated with the downdrafts spreading out in advance of squall lines and thunderstorms. Resulting damage is usually confined to narrow zones like that caused by tornadoes; however, the winds are all in one direction (straight-line winds). Plume Blight Visibility impairment caused by air pollution plumes aggregated from individual sources. Plume Impingement The collision of a plume with topography that rises above the plume altitude; often a temporary condition that occurs as the plume sweeps by the face of a hill as the wind shifts. Plume-dominated Fire A fire whose behavior is governed primarily by the local wind circulation produced in response to the strong convection above the fire rather than by the general wind. Pluvial In hydrology, anything that is brought about directly by precipitation. PMD Prognostic Discussion PMO Port Meteorological Officer. PNA Pacific North American teleconnection PNHDL Panhandle --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .