Subj : Wx Terms (P)(3)
To : All
From : Daryl Stout
Date : Sat Jun 17 2017 09:00 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.
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