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Weather Term Definitions
- Parhelion: The scientific name for sun dogs.
- Partly Cloudy: Sky condition when between 3/10 and 7/10 of the sky is covered. Used more frequently at night.
- Partly Sunny: Similar to partly cloudy. Used to emphasize daytime sunshine.
- Peak Gust: The highest instantaneous wind speed observed or recorded.
- Period: Time, in seconds, between the passage of consecutive ocean wave crests past a fixed location. (Abbreviated T).
- PIREP: Pilot Report. A report of in-flight weather by an aircraft pilot or crew member.
- POES: Polar Orbiting Environmental Satellite. NOAA's polar satellite series.
- Polar Orbiting Satellite: A satellite that orbits the Earth from pole to pole at an altitude of approximately 500 miles as the Earth rotates underneath it. This allows higher resolution images than Geostationary Satellites, but with less frequent coverage for any specific land area.
- Polar Air: A mass of very cold, very dry air that forms in polar regions.
- Polar front: The semi-permanent, semi-continuous front that encircles the northern hemisphere separating air masses of tropical and polar origin.
- Polar Jet: Jet stream that is the boundary between the polar air and the subtropical air. 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.
- Pollutant: Strictly too much of any substance in the wrong place or at the wrong time is a pollutant. More specifically, atmospheric pollution may be defined as the presence of substances in the atmosphere, resulting from man-made activities or from natural processes, causing adverse effects to man and the environment.
- Precipitation: Liquid or solid water that falls from the atmosphere and reaches the ground.
- Pressure: The force exerted by the interaction of the atmosphere and gravity. Also known as atmospheric pressure.
- 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 Gradient: The rate of decrease of pressure with distance at a fixed level.
- 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 the 3-hour period preceding an observation.
- Prevailing Wind: The direction from which the wind blows most frequently in any location.
- Probability of Precipitation (PoP): The average probability (likelihood) that any given point in the forecast area will observe 0.01 inches of precipitation (water) for a given forecast period (usually twelve hours unless otherwise expressed). This is expressed in percent, 0% meaning dry, and 100% meaning certain precipitation.
- 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.
- Psychrometer: An instrument used for measuring the water vapor content of the atmosphere. It consists of two thermometers, one of which is an ordinary glass thermometer, while the other has its bulb covered with a jacket of clean muslin which is saturated with distilled water prior to use.
