Subj : Wx Terms (P)(4) To : All From : Daryl Stout Date : Mon Jul 17 2017 12:08 am Power A radar equation to describe the amount of power that a radar emits. P = I * V (or) P = V2 / R (or) P = I2 / R where I is current (amps), V is voltage (volts), R is resistance (ohms), P is power (watts). PPI Plan Position Indicator PPINE Plan Position Indicates No Echoes, referring to the fact that a radar detects no precipitation within its range. An intensity-modulated display on which echo signals are shown in plain view with range and azimuth angle displayed in polar coordinates, forming a map-like display. Each PPI is taken at a single, fixed elevation angle, and thus forms a cone of coverage in space. PPIs may be run in sequence, creating a "volume scan". PQPF Probabilistic QPF; a form of QPF (see below) that includes an assigned probability of occurrence for each numerical value in the forecast product. PRBLTY Probability PRBLY probably PRCP Precipitation Pre-Frontal Squall Line A line of thunderstorms that precedes an advancing cold front. Pre-Frontal Trough An elongated area of relatively low pressure preceding a cold front that is usually associated with a shift in wind direction. Pre-Hurricane Squall Line It is often the first serious indication that a hurricane is approaching. It is a generally a straight line and resembles a squall-line that occurs with a mid-latitude cold front. It is as much as 50 miles or even more before the first ragged rain echoes of the hurricane's bands and is usually about 100 to 200 miles ahead of the eye, but it has been observed to be as much as 500 miles ahead of the eye in the largest hurricanes. PRECD Precede Precipitable 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 over a given location, usually extending from the surface to 300 mb. Precipitation The process where water vapor condenses in the atmosphere to form water droplets that fall to the Earth as rain, sleet, snow, hail, etc. Precipitation Attenuation The loss of energy that radar beam experiences as it passes through an area of precipitation. Precipitation Mode The standard, or default, operational mode of the WSR-88D. The radar automatically switches into precipitation mode from clear-air mode if the measured reflectivity exceeds a specific threshold value. The precipitation mode of NEXRAD is more sensitive than previous weather radars. The minimum detectable reflectivity in NEXRAD's precipitation mode is 5 dBZ, compared to 28 dBZ with the old WSR-57. Precipitation Processing System The WSR-88D system that generates 1-hour running, 3-hourly, and running storm total precipitation accumulations. Five functional steps are performed to calculate the best estimate of precipitation: 1) development of a sectorized hybrid scan, 2) conversion to precipitation rate, 3) precipitation accumulation, 4) adjustment using rain gages, 5) product update. Precision The accuracy with which a number can be represented, i.e., the number of digits used to represent a number. Predominant Wind The wind that prevails and generates the local component of the significant sea conditions across the forecast area. This is the wind included in all marine forecast products and is defined as a 10-meter wind, except over the nearshore marine zones where it is defined to be the wind at a 3-meter height. Preliminary Report Now known as the "Tropical Cyclone Report". A report summarizing the life history and effects of an Atlantic or eastern Pacific tropical cyclone. It contains a summary of the cyclone life cycle and pertinent meteorological data, including the post-analysis best track (six-hourly positions and intensities) and other meteorological statistics. It also contains a description of damage and casualties the system produced, as well as information on forecasts and warnings associated with the cyclone. NHC writes a report on every tropical cyclone in its area of responsibility. PRES Pressure Prescribed Fire A management ignited or natural wildland fire that burns under specified conditions where the fire is confined to a predetermined area and produces the fire behavior and fire characteristics required to attain planned fire treatment and resource management objectives. Present Movement The best estimate of the movement of the center of a tropical cyclone at a given time and given position. This estimate does not reflect the short-period, small scale oscillations of the cyclone center. Present Weather The type of weather observed at the reporting time. These conditions may include types and intensity of precipitation such as light rain or heavy snow, as well as the condition of the air environment such as foggy, hazy or blowing dust. Pressure The exertion of force upon a surface by a fluid (e.g., the atmosphere) in contact with it. Pressure Altimeter An aneroid barometer calibrated to indicate altitude in feet instead of units of pressure. It is read accurately only in a standard atmosphere and when the correct altimeter setting is used. Pressure Altitude The altitude in standard atmosphere at which a given pressure will be observed. It is the indicated altitude of a pressure altimeter at an altitude setting of 29.92 inches of mercury, and is therefore the indicated altitude above the 29.92 constant pressure surface. Pressure Change The net difference between the barometric pressure at the beginning and ending of a specified interval of time, usually the three hour period preceding an observation. Pressure Characteristic The pattern of the pressure change during the specified period of time, usually the three hour period preceding an observation. This is recorded in three categories: falling, rising, or steady. Pressure Couplet It is an area where you have a high pressure area located adjacent to a low pressure area. Pressure Falling Rapidly A decrease in station pressure at a rate of 0.06 inch of mercury or more per hour which totals 0.02 inch or more. Pressure Gage A device for registering the pressure of solids, liquids, or gases. It may be graduated to register pressure in any units desired. Pressure Gradient The amount of pressure change occurring over a given distance. Pressure Gradient Force A three-dimensional force vector operating in the atmosphere that accelerates air parcels away from regions of high pressure and toward regions of low pressure in response to an air pressure gradient. Usually resolved into vertical and horizontal components. Pressure Head Energy contained by fluid because of its pressure, usually expressed in feet of fluid (foot pounds per pound). Pressure Ice Floating sea, river, or lake ice that has been deformed, altered, or forced upward in pressure ridges by the lateral stresses of any combination of wind, water currents, tides, waves, and surf. Pressure Induced Wave A rare type of wave that does not develop from wind or seismic activity. Instead, these waves develop as a pressure perturbation moves over the water surface. The water surface adjusts to account for the atmospheric pressure change. As atmospheric pressure decreases, the force exerted upward by the water increases, creating a pressure induced wave. Pressure Jump A sudden, sharp increase in atmospheric pressure, typically occurring along an active front and preceding a storm. --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .