Still gasAny form or mixture of gases produced in refineries by distillation, cracking, reforming, and other processes.
Stilling BasinConcrete portion downstream from conduit, tunnel, or control structure. A pool, usually lined with reinforced concrete, located below a spillway, gate, or…
STJSubtropical Jet - this jet stream is usually found between 20° and 30° latitude at altitudes between 12 and 14 km.
StoplogsLarge logs, planks, cut timbers, steel or concrete beams placed on top of each other with their ends held in guides between walls or piers to close an…
StormAny disturbed state of the atmosphere, especially affecting the Earth's surface, and strongly implying destructive and otherwise unpleasant weather.
Storm DataThis National Climatic Data Center (NCDC) monthly publication documents a chronological listing, by states, of occurrences of storms and unusual weather…
Storm MotionThe speed and direction at which a thunderstorm travels.
Storm RelativeMeasured relative to a moving thunderstorm, usually referring to winds, wind shear, or helicity.
Storm Relative Mean Radial Velocity Map(SRM): This WSR-88D radar product depicts a full 360º sweep of radial velocity data with the average motion of all identified storms subtracted out.
Storm Relative Mean Radial Velocity Regi(SRR): This WSR-88D radar product depicts a 27 nm by 27 nm region of storm relative mean radial velocity centered on a point which the operator can…
Storm ScaleReferring to weather systems with sizes on the order of individual thunderstorms. See synoptic scale and mesoscale.
Storm SurgeAn abnormal rise in sea level accompanying a hurricane or other intense storm, whose height is the difference between the observed level of the sea…
Storm TideThe actual level of sea water resulting from the astronomic tide combined with the storm surge.
Storm Total PrecipitationThis radar image is an estimate of accumulated rainfall since the last time there was a one-hour, or more, break in precipitation.
Storm Tracking InformationThis WSR-88D radar product displays the previous, current, and projected locations of storm centroids (forecast and past positions are limited to one hour…
Storm WarningA warning of sustained surface winds, or frequent gusts, in the range of 48 knots (55 mph) to 63 knots (73 mph) inclusive, either predicted or occurring…
Stormwater DischargePrecipitation that does not infiltrate into the ground or evaporate due to impervious land surfaces but instead flows onto adjacent land or water areas…
Straight-Line HodographThe name pretty well describes what it looks like on the hodograph. What causes this shape is a steady increase of winds with height (vertical wind shear).
Straight-line WindsGenerally, any wind that is not associated with rotation, used mainly to differentiate them from tornadic winds.
StratiformHaving extensive horizontal development, as opposed to the more vertical development characteristic of convection.
Stratiform Rings and BandsThese occur between the active convective bands of a hurricane outside of the eye wall.
StratocumulusLow-level clouds, existing in a relatively flat layer but having individual elements. Elements often are arranged in rows, bands, or waves.
StratopauseThe boundary between the stratosphere and mesosphere.
StratosphereThe region of the atmosphere extending from the top of the troposphere to the base of the mesosphere, an important area for monitoring stratospheric ozone.
Stratospheric OzoneIn the stratosphere, ozone has beneficial properties where it forms an ozone shield that prevents dangerous radiation from reaching the Earth's surface.
StratusA low, generally gray cloud layer with a fairly uniform base. Stratus may appear in the form of ragged patches, but otherwise does not exhibit individual…
Stream lineAn imaginary line within the flow which is everywhere tangent to the velocity vector.
StreamflowDischarge that occurs in a natural channel.
StriationsGrooves or channels in cloud formations, arranged parallel to the flow of air and therefore depicting the airflow relative to the parent cloud.
StrikeStrike means a labor dispute wherein employees engage in a concerted stoppage of work (including stoppage by reason of the expiration of a collective…
Strip miningCutting deep trenches to remove minerals such as coal and phosphate found near the earth's surface in flat or rolling terrain. See surface mining.
Subbituminous coalA dull, black coal of rank intermediate between lignite and bituminous coal. See coal.
SublimationThe transition of a substance from the solid phase directly to the vapor phase, or vice versa, without passing through an intermediate liquid phase.
Sublimation of iceThe transition of water from solid to gas without passing through the liquid phase.
SubrefractionThe bending of the radar beam in the vertical which is less than under standard refractive conditions.
SubsidenceSinking or settlement of the land surface, due to any of several processes. As commonly used, the term relates to the vertical downward movement of…
Subsidence InversionA temperature inversion that develops aloft as a result of air gradually sinking over a wide area and being warmed by adiabatic compression, usually…
SubstationAn electrical installation containing power conversion (and sometimes generation) equipment, such as transformers, compensators, and circuit breakers.
Subsurface Storm FlowThe lateral motion of water through the upper layers until it enters a stream channel. This usually takes longer to reach stream channels than runoff.
Subtle Heavy Rainfall SignatureThis heavy rain signature is often difficult to detect on satellite. These warm top thunderstorms are often embedded in a synoptic-scale cyclonic…
Subtropical CycloneA non-frontal low pressure system that has characteristics of both tropical and extratropical cyclones.
Subtropical DepressionA subtropical cyclone in which the maximum 1-minute sustained surface wind is 33 knots (38 mph) or less.
Subtropical Jet(Abbrev. STJ) - this jet stream is usually found between 20° and 30° latitude at altitudes between 12 and 14 km.
Subtropical StormA subtropical cyclone in which the maximum 1-minute sustained surface wind is 34 knots (39 mph) or more.
Suction VortexA small but very intense vortex within a tornado circulation. Several suction vortices typically are present in a multiple-vortex tornado.
Sudden Commencement (SC)In solar-terrestrial terms, an abrupt increase or decrease in the northward component of the geomagnetic field, which marks the beginning of a geomagnetic…
Sudden Impulse (SI+ or SI-)In solar-terrestrial terms, a sudden perturbation of several gammas in the northward component of the low-latitude geomagnetic field, not associated with…
Sudden Ionospheric Disturbance (SID)In solar-terrestrial terms, HF propagation anomalies due to ionospheric changes resulting from solar flares, proton events and geomagnetic storms.
Sulfate AerosolsParticulate matter that consists of compounds of sulfur formed by the interaction of sulfur dioxide and sulfur trioxide with other compounds in the…
Sulfur cycleCyclic movement of sulfur in different chemical forms from the environment, to organisms, and then back to the environment.
Sulfur dioxide (SO<sub>2</sub>)A compound composed of one sulfur and two oxygen molecules. Sulfur dioxide emitted into the atmosphere through natural and anthropogenic processes is…
Sulfur Hexafluoride (SF6)A colorless gas soluble in alcohol and ether, slightly soluble in water. A very powerful greenhouse gas used primarily in electrical transmission and…
Sulfur Hexafluoride (SF<sub>6</sub>)A colorless gas soluble in alcohol and ether, slightly soluble in water. A very powerful greenhouse gas used primarily in electrical transmission and…
Summation PrincipleThis principle states that the sky cover at any level is equal to the summation of the sky cover of the lowest layer plus the additional sky cover…
SummerTypically the warmest season of the year during which the sun is most nearly overhead.
Summer SolsticeThe time at which the sun is farthest north in the Northern Hemisphere, on or around June 21.
Sun PillarA bright column above or below the sun produced by the reflection of sunlight from ice crystals.
Sun PointingAlignment of the radar antenna by locating the position of the sun in the sky, which has an exactly known position given the radar's location and the…
sundogA colored luminous spot produced by refraction of light through ice crystals that appears on either side of the sun. Also called parhelion.
SunnyWhen there are no opaque (not transparent) clouds. Same as Clear.
SunriseThe phenomenon of the sun's daily appearance on the eastern horizon as a result of the earth's rotation.
SunsetThe phenomenon of the sun's daily disappearance below the western horizon as a result of the earth's rotation.
SunspotDark areas on the Sun created by strong magnetic fields beneath the Sun’s surface.
Sunspot Group ClassificationA: A small single unipolar sunspot or very small group of spots without penumbra. B: Bipolar sunspot group with no penumbra.
Sunspot NumberIn solar-terrestrial terms, a daily index of sunspot activity (R), defined as R = k (10 g + s) where S = number of individual spots, g = number of sunspot…
Super TyphoonTyphoon having maximum sustained winds of 130 knots (150 mph) or greater.
SupercellShort reference to Supercell Thunderstorm; potentially the most dangerous of the convective storm types.
Supercell ThunderstormPotentially the most dangerous of the convective storm types. Storms possessing this structure have been observed to generate the vast majority of…
SupercoolTo cool a liquid below its freezing point without solidification or crystallization.
Supercooled Liquid WaterIn the atmosphere, liquid water can survive at temperatures colder than 0 degrees Celsius; many vigorous storms contain large amounts of supercooled…
SuperrefractionBending of the radar beam in the vertical which is greater than sub-standard refractive conditions.
supersaturated airA condition that occurs in the atmosphere when the relative humidity is greater that 100 percent.
Surcharge CapacityThe volume of a reservoir between the maximum water surface elevation for which the dam is designed and the crest of an uncontrolled spillway, or the…
Surf ZoneArea of water between the high tide level on the beach and the seaward side of the breaking waves.
Surf Zone Forecast(SRF) - A National Weather Service routine or event driven forecast product geared toward non-boating marine users issued for an area extending from the…
surface albedoThe fraction of incoming solar radiation at a surface (i.e., land, cloud top) that is effectively reflected by that surface.
surface conditionState of the surface, including vegetation, land use, surface type, roughness, and such; often provided in model output.
Surface Energy BudgetThe energy or heat budget at the earth's surface, considered in terms of the fluxes through a plane at the earth-atmosphere interface.
Surface ImpoundmentAn indented area in the land's surface, such as a pit, pond, or lagoon.
Surface miningRemoval of soil, sub-soil, and other strata and then extracting a mineral deposit found fairly close to the earth's surface. See strip mining.
surface moisture fluxThe vertical flux of surface moisture due to atmospheric turbulent transport.
Surface observationSurface observation A meteorological observation made on the Earth's surface in contrast with an upper-air observation).
Surface RunoffPrecipitation, snow melt, or irrigation in excess of what can infiltrate the soil surface and be stored.
surface skin temperatureThe radiative surface skin temperature, from an infrared thermometer measuring the narrowband radiating temperature of the ground surface in its field of…
surface stressThe vertical flux of momentum near the surface as the the ambient flow interacts with the land/water surface.
Surface WaterWater on the Earth's surface that is directly exposed to the atmosphere, as distinguished from water in the ground (groundwater).
Surface Weather ChartAn analyzed synoptic chart of surface weather observations. A surface chart shows the distribution of sea-level pressure (therefore, the position of…
Surface windSurface wind Wind blowing near the Earth's surface. It is measured, by convention, at a height of 10 m above ground in an area where the distance between…
Surface-based ConvectionConvection occurring within a surface-based layer, i.e., a layer in which the lowest portion is based at or very near the earth's surface.