Subj : Wx Terms (P)(2)
To   : All
From : Daryl Stout
Date : Tue Oct 17 2017 12:07 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



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