PDS Watch - [Slang], a tornado watch with enhanced wording
(Particularly Dangerous Situation).
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.
Popcorn Convection - [Slang], 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
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 CG - 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-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.
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.
PPINE - Plan Position Indicates No Echoes, referring to the
fact that a radar detects no precipitation within its range.
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.
Pseudo-Cold Front - A boundary between a supercell's inflow
region and the rear-flank downdraft (or RFD). It extends outward
from the mesocyclone centre, usually toward the south or southwest
(but occasionally bows outward to the east or southeast in the case
of an occluded mesocyclone), and is characterized by advancing of
the downdraft air toward the inflow region. It is a particular form
of gust front. See also pseudo-warm front.
Pseudo-Warm Front - A boundary between a supercell's inflow
region and the forward-flank downdraft (or FFD). It extends outward
from at or near the mesocyclone centre, usually toward the east or
southeast, and normally is either nearly stationary or moves
northward or northeastward ahead of the mesocyclone. See pseudo-cold
front and beaver tail.
Pulse Storm - A thunderstorm within which a brief period
(pulse) of strong updraft occurs, during and immediately after which
the storm produces a short episode of severe weather. These storms
generally are not tornado producers, but often produce large hail
and/or damaging winds. See overshooting top, cyclic storm.
PVA - Positive Vorticity Advection. 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.