Weather Glossary – P


PACIFIC HIGH – A semipermanent anticyclone located in the Eastern North Pacific.

PACKAGE– A compilation of analysis and forecast charts and their interpretation.

PARTLY CLOUDY (PARTLY SUNNY) – Sky condition when between 3/10 and 7/10 of the sky is covered.

PBL– Planetary Boundary Layer. The lowest level of the atmosphere where friction is an important force and vertical mixing is common.

PERMAFROST – a soil layer below the surface of tundra regions that remains frozen permanently.

PD – Period

PG– Pressure gradient. Tightening pressure gradient indicates stronger winds.

PHASING– When two separate short waves come together to form one wave. Also, when upper and lower level features are positioned so that each provides energy to the other, it is said that the features are in phase with one another.

PINEAPPLE CONNECTION – A warm and moist flow of air with origins from the tropics which precedes major winter storms. It can bring significant rain and snow to the Pacific Northwest.

POP – Probability of Precipitation. This is the chance the NWS gives to precipitation across there forecast region. It may also refer to the POP a forecast model is predicting.

POSITIVE ISOTHERMAL VORTICITY ADVECTION (PIVA)– Advection of higher values of vorticity by the thermal wind on a map of vorticity and thickness contours. Implies an area of rising motion.

POSITIVE TILTED TROUGH– A trough which tilts from the northeast toward the southwest. Often a trough is positive tilted in it’s development stage.

POTENTIAL INSTABILITY- Also known as convective instability. Instability caused by dry air advecting over warm and humid PBL air. Lapse rate of temperature increases if lifting occurs.

PRECIPITABLE WATER (PW, PCPTBL WTR or H2O)– Total amount of water vapor in a layer of air, expressed in inches. Normally taken between 1000 and 500 mb. Higher values of precipitable water indicate a deep moisture layer, increasing the potential for heavy precipitation amounts.

PRECIPITATION (PCPN) -Liquid or solid water molecules that fall from the atmosphere and reach the ground.

PRESSURE –The force exerted by the interaction of the atmosphere and gravity. Also known as atmospheric pressure.

PROFILER– A remote ground-based sensing instrument that measures wind speed and direction at different levels of the atmosphere. The new National Weather Service WSR-88D radar has this capability, and its vertical wind profile is called a VAD Wind Profile (or VWP). VAD stands for Velocity Azimuth Display.

PROG– Model forecasted output

PROGRESSIVE FLOW or PROGRESSIVE PATTERN– An upper level flow pattern in which storm systems move along at a fairly regular pace.

PTWC – Pacific Tsunami Warning Center, located in Honolulu, HI.

PUNCH (or PUSH)– A fast moving mass of air (e.g. dry punch, cold punch)

PWAT(S)– Precipitable Water value(s)