Subj : Wx Terms (P)(1)
To   : All
From : Daryl Stout
Date : Thu Aug 17 2017 12:04 am

PAC
Pacific

Pacific Decadal Oscillation
(Abbrev. PDO) - a recently described pattern of climate variation similar
to ENSO though on a timescale of decades and not seasons. It is
characterized by SST anomalies of one sign in the north-central Pacific
and SST anomalies of another sign to the north and east near the
Aleutians and the Gulf of Alaska. It primarily affects weather patterns
and sea surface temperatures in the Pacific Northwest, Alaska, and
northern Pacific Islands.

Palmer Drought Severity Index
(Abbrev. PDSI) - an index used to gage the severity of drought conditions
by using a water balance equation to track water supply and demand. This
index is calculated weekly by the National Weather Service.

Pan Pan
A headline within National Weather Service high seas forecasts
transmitted via the GMDSS to indicate that a hurricane or hurricane
force winds are forecast.

Pancake Ice
In hydrologic terms, circular flat pieces of ice with a raised rim; the
shape and rim are due to repeated collisions.

Panhandle Hook
Low pressure systems that originate in the panhandle region of Texas and
Oklahoma which initially move east and then "hook" or recurve more
northeast toward the upper Midwest or Great Lakes region. In winter,
these systems usually deposit heavy snows north of their surface track.
Thunderstorms may be found south of the track.

Parameter
A subset of the group of evaluations that constitute each element of an
observation.

Parapet Wall
In hydrologic terms, a solid wall built along the top of the dam for
ornament, safety, or to prevent overtopping.

Parcel
A volume of air small enough to contain uniform distribution of its
meteorological properties and large enough to remain relatively
self-contained and respond to all meteorological processes.

Parhelion
The scientific name for sun dogs. Either of two colored luminous spots
that appear at roughly 22 degrees on both sides of the sun at the same
elevation. They are caused by the refraction of sunlight passing
through ice crystals. They are most commonly seen during winter in the
middle latitudes and are exclusively associated with cirriform clouds.
They are also known as mock suns.

Partial Beam Filling
A limitation of the rainfall estimation techniques used by NEXRAD. At
far ranges from the radar, a storm may occupy only a portion of the
radar beam (which may be several miles across). However, the radiation
received by the radar antenna consists of the average reflectivity
across the entire beam, so the reflectivity and associated rainfall
rates are underestimated.

Partial-Duration Flood Series
In hydrologic terms, a list of all flood peaks that exceed a chosen
base stage or discharge, regardless of the number of peaks occurring
in a year.

Particle Trajectory Model
A computer sub-model that tracks the trajectories of multiple particles
that are released into an atmospheric flow model.

Partly Cloudy
When the predominant/average sky condition is covered 3/8 to 4/8 with
opaque (not transparent) clouds. Same as Partly Sunny.

Partly Sunny
When the predominant/average sky condition is covered 3/8 to 4/8 with
opaque (not transparent) clouds. Same as Partly Cloudy.

Pascal
The unit of pressure produced when one newton acts on one square meter
(1 N/m2). It is abbreviated Pa.

PAT
Pattern

PBL
Probable

PC-GRIDDS
PC-Gridded Interactive Display and Diagnostic System - Allows the
forecaster to view fields of gridded model output in contour or vector
format. By doing this, the forecaster can extract relevant information
from the numerical model grid-point data.

PCPN
Precipitation

PCT
precent

PD
Period

PDI
Palmer Drought Index

PDMT
Predominant

PDO
Pacific Decadal Oscillation - a recently described pattern of climate
variation similar to ENSO though on a timescale of decades and not
seasons. It is characterized by SST anomalies of one sign in the
north-central Pacific and SST anomalies of another sign to the north
and east near the Aleutians and the Gulf of Alaska. It primarily
affects weather patterns and sea surface temperatures in the Pacific
Northwest, Alaska, and northern Pacific Islands. Two main characteristics
distinguish PDO from El Ni�o/Southern Oscillation (ENSO): first,
20th century PDO "events" persisted for 20-to-30 years, while typical
ENSO events persisted for 6 to 18 months; second, the climatic
fingerprints of the PDO are most visible in the North Pacific/North
American sector, while secondary signatures exist in the tropics-
the opposite is true for ENSO. Several independent studies found
evidence of just two full PDO cycles in the past century: cool" PDO
regimes prevailed from 1890-1924 and again from 1947-1976, while
"warm" PDO regimes dominated from 1925-1946 and from 1977 through
(at least) the mid-1990's. Causes for the PDO are not currently known.
Likewise, the potential predictability for this climate oscillation are
not known.

PDS
Particularly Dangerous Situation (PDS) wording is used in rare
situations when long-lived, strong and violent tornadoes are possible.
This enhanced wording may also accompany severe thunderstorm watches
for intense convective wind storms.

PDS Watch
The Particularly Dangerous Situation (PDS) wording is used in rare
situations when long-lived, strong and violent tornadoes are possible.
This enhanced wording may also accompany severe thunderstorm watches
for intense convective wind storms.

PDSI
Palmer Drought Severity Index - an index used to gage the severity of
drought conditions by using a water balance equation to track water
supply and demand. This index is calculated weekly by the National
Weather Service.

PDT
Pacific Daylight Time

Peak Discharge
In hydrologic terms, the rate of discharge of a volume of water passing
a given location.

Peak Gust
The highest instantaneous wind speed observed or recorded.

Peak Pulse
The amount of power transmitted by a radar during a given pulse. Note
that because these pulses are widely spaced, the average power will be
much smaller.

Peak Wind Speed
The maximum instantaneous wind speed since the last observation that
exceeded 25 knots.

Pendant Echo
Radar signature generally similar to a hook echo, except that the hook
shape is not as well defined.

Penetrating Top
Same as Overshooting Top; a dome-like protrusion above a thunderstorm
anvil, representing a very strong updraft and hence a higher potential
for severe weather with that storm. A persistent and/or large
overshooting top (anvil dome) often is present on a supercell. A
short-lived overshooting top, or one that forms and dissipates in
cycles, may indicate the presence of a pulse storm.

Penumbra
In solar-terrestrial terms, the sunspot area that may surround the
darker umbra or umbrae. It consists of linear bright and dark elements
radial from the sunspot umbra.

Perched Groundwater
In hydrologic terms, local saturated zones above the water table which
exist above an impervious layer of limited extent.

Percolation
In hydrologic terms, the movement of water, under hydrostatic pressure,
through the interstices of a rock or soil, except the movement through
large openings such as caves.

Percolation Path
In hydrologic terms, the course followed by water moving or percolating
through any other permeable material, or under a dam which rests upon a
permeable foundation.



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