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. --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .