Subj : Wx Terms (P)(4)
To : All
From : Daryl Stout
Date : Fri Nov 17 2017 12:05 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.
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