Saffir-Simpson Scale - a scale developed to estimate the possible damage a hurricane’s sustained winds and storm surge could do to a coastal area

SAME - see Specific Area Message Encoding

Sandstorm (SS) - particles of sand carried aloft by strong winds. The sand particles are mostly confined to the lowest ten feet, and rarely rise more than fifty feet above the ground. One kind of sandstorm is a haboob.

Santa Ana Wind - in southern California, a weather condition in which strong, hot, dust-bearing winds descend to the Pacific Coast around Los Angeles from elevated, inland desert regions.

SAT - see Satellite

SAT - Saturday

Satellite (SAT, SATL, or STLT) - an object that orbits a larger object. In weather, we usually refer to a man-made object that orbits the Earth and provides weather data as a satellite.

SATL - see Satellite

Saturation (of air) - the presence of the most water possible in the air. Saturation depends on the pressure and temperature of the air. If more water is added to already saturated air, the excess will be condensed from the air (moving from gas to liquid form).

Saturation Vapor Pressure - see Equilibrium Vapor Pressure

SBCAPE - CAPE calculated using a surface-based parcel

SBND - southbound

SBSD - subside

SC - South Carolina

SC - see Stratocumulus

Scary Looking Cloud (SLC) - a dark, ominous-looking cloud. Many SLCs are part of the turbulent flow (which is often seen as small areas of rotation) under a shelf cloud. This rotation does not usually produce tornadoes; nevertheless, it has been known to lead to "tornado" reports. Most SLCs are harmless.

Scattering - the process by which small particles are forced to change their direction of motion

Science and Operations Officer (SOO) - a position in a National Weather Service Forecast Office. The primary focus of the Science and Operations Officer is to ensure the scientific integrity of the hydrometeorological products and services provided to the public by the WFO. He or she also leads or participates in joint research projects with the collocated university/research center. The SOO monitors and evaluates the accuracy and scientific basis of forecast and warning products and services provided by the forecast office.

SCT - scattered

Scud (or Fractus) - small, ragged, low cloud fragments that are unattached to a larger cloud base. They are often seen with and behind cold fronts and thunderstorm gust fronts. Scud can also rise up and eventually form part of a wall cloud on a supercell thunderstorm.

SD - South Dakota

SE - southeast

Sea Breeze - a cooling breeze blowing generally inland from the sea in the daytime, caused by the temperature difference when the sea surface is cooler than the adjacent land

Sea Level Pressure (SLP) - the atmospheric pressure computed from the station pressure for the elevation of the station above mean sea level

Sea Surface Temperature (SST) - this term refers to the mean/average temperature of the ocean in the upper few meters.

Second Law of Thermodynamics - entropy (a measure of chaos) tends to increase in energy systems. For example, solid crystals, the most organized form of matter, have low values of entropy. Gases, which are highly disorganized, have high values of entropy.

SELY - southeasterly

Sensible Heat - the heat absorbed or transmitted when the temperature of a substance changes but the substance does not change state

SERN - southeastern

Severe Thunderstorm - a thunderstorm with wind gusts of 50 knots (58 mph) or greater, hail at least one inch (quarter-sized) in diameter, and/or a tornado or funnel cloud

Severe Thunderstorm Watch (WW) - conditions are favorable for the development of severe thunderstorms.

Severe Weather Threat Index (SWEAT) - incorporates instability, wind shear, and wind speeds. Values of 250-300 or greater indicate a greater potential for severe weather.

SEWD - southeastward

SFC - surface

SG - see Snow Grains

SGFNT - significant

Shear - see Wind Shear

Shelf Cloud - a low, horizontal wedge-shaped arcus cloud, associated with a thunderstorm gust front (or occasionally with a cold front, even in the absence of thunderstorms). Unlike the roll cloud, the shelf cloud is attached to the base of the parent cloud above it (usually a thunderstorm). Rising cloud motion often can be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent, boiling, and wind-torn. Many shelf clouds are SLCs, and tornadoes usually do not form in this region.

SHFT - shift

SHLW - shallow

Shortwave (or Shortwave Trough) (S/W, S/WV, SHRTWV) - a disturbance in the middle or upper part of the atmosphere that induces upward motion ahead of it (it creates lift)

Shortwave Radiation - in meteorology, radiation having a wavelength equal to or less than that of visible light

Shower (SHWR) - intermittent precipitation from a convective cloud, generally of short duration

SHRA - rain showers

SHRAS - showers

SHRT - short

SHRTWV - see Shortwave

SHSN - see Snow Shower

SHUD - should

SHWR - see Shower

SIG - significant

SI Units - see International System of Units

Skew-T, Log P Diagram - skewed temperature, logarithmic pressure diagram. This is the chart used to plot radiosonde data (a sounding).

Sky Cover - a term used to describe the amount of sky covered or concealed by clouds or obscuring phenomena. Classifications for sky cover include clear, broken, partly cloudy, and overcast.

SKYWARN - a nationwide network of volunteer weather spotters who report to and are trained by the National Weather Service. These spotters report many forms of significant or severe weather such as severe thunderstorms, tornadoes, hail, heavy snow, or flooding.

SL - sea level

SLC - see Scary Looking Cloud

SLD - solid

Sleet (PL) - frozen or partly frozen falling rain; ice pellets

SLGT - slight

Slight Chance - in probability of precipitation, usually a 20 percent chance.

Slight Risk (of severe thunderstorms) - severe thunderstorms are expected to affect between 2 and 5 percent of the area. A slight risk generally implies that severe weather events are expected to be isolated.

SLO - slow

SLP - see Sea Level Pressure

SLT - slight

SLY - southerly

SM - see Statute Mile

Smog - a natural fog made heavier and darker by smoke and chemical fumes

SN - see Snow

Snow (SN, SNW) - precipitation in the form of small hexagonal ice crystals formed directly from the water vapor of the air at a temperature of less than 0 degrees Celsius (below 32 degrees Fahrenheit)

Snowflake - either a single hexagonal (6-sided) ice crystal that grows through deposition, or an accumulation of ice crystals that stick together and fall as a unit.

Snow Flurries - popular term for a light snow shower

Snow Grains (SG) - precipitation consisting of white, opaque ice particles usually less than 1mm in diameter.

Snow Pellets - precipitation in the form of white, opaque, approximately round ice particles, about 2 to 5 mm in diameter, with a snow-like structure

Snow Shower (SHSN) - intermittent snow falling from a convective cloud

Snow Squall - an intense, but limited duration, period of moderate to heavy snowfall accompanied by strong, gusty surface winds and possibly lightning. Snow accumulation may be significant.

SNW - snow or snowfall; see Snow

SNWFL - snowfall

SODAR - see Sonic Detection and Ranging

SOI - see Southern Oscillation Index

Solar Constant - the total power collected per unit area. The units are meters squared. Since the orbit of Earth is an ellipse (the Sun-Earth distance varies), the solar constant changes with time.

Solar Radiation - the radiation emitted by the sun

Solid - one of the three basic phases of matter; a substance that does not flow under moderate stress

SOLN - solution

SOLNS - solutions

Solstice - the times of the year when the sun appears to the farthest north or south of the equator, lying above either the Tropic of Cancer or the Tropic of Capricorn

Sonic Detection and Ranging (SODAR) - a type of wind profiler that measures the scattering of sound waves by turbulence, giving information on wind speed at various heights above the ground. SODAR is similar to radar, except that sound waves instead of radio waves are used for detection.

SOO - see Science and Operations Officer

Sounding - a plot of the vertical profile of temperature and dew point (and often winds) above a fixed location; used extensively in weather forecasting. See Skew-T, Log P Diagram.

Sounding-based Stability Index - an index calculated from balloon observations (e.g., CAPE, Lifted Index, K-Index, Bulk Richardson Number, Total-Totals Index) that provides guidance about the potential organization, type, and severity of thunderstorms (supercell, multi-cell, etc.)

Southern Oscillation - the reversal of typical surface air pressure patterns across the tropical Pacific that occurs during a major El Niño event

Southern Oscillation Index (SOI) - an index that monitors the Southern Oscillation using the difference between sea level pressures at Darwin, Australia and Tahiti. Large negative values of the SOI indicate a warm event (El Niño) and large positive values indicate a cold event (La Niña).

Space Weather Prediction Center (SWPC) - one of 9 NCEP centers; provides space weather alerts and warnings for disturbances that can affect people and equipment working in space and on Earth. It is located in Boulder, Colorado.

Spaghetti Plot - an ensemble (group) of forecasts or observed values that looks like spaghetti. For example, if we plot critical thickness lines on a map, most of the lines will not match up. Instead, they tend to look like spaghetti tossed on a plate.

SPC - see Storm Prediction Center

SPD - speed

Specific Area Message Encoding (SAME) - a tone alert system that allows NOAA Weather Radio receivers to sound an alert for only certain weather conditions or within a limited geographic area such as a county.

Specific Heat - the amount of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius; the higher the specific heat, the more heat is required to warm a substance. For example, water has a high specific heat--it takes a long time for it to heat up or to cool down. The ground has a relatively low specific heat (compared to water)--it takes a short time for it to heat up or to cool down.

Specific Volume - volume per unit mass; the reciprocal of density

Speed Shear - the component of wind shear resulting from a change in wind speed with height (e.g., southwesterly winds of 20 mph at 10,000 feet increasing to 50 mph at 20,000 feet). Speed shear is an important factor in severe weather development, especially in the middle and upper levels of the atmosphere.

Spin-up - slang for a small-scale vortex initiation, such as what may be seen when a gustnado, landspout, or suction vortex forms.

SPKL - sprinkle

Splitting Storm - a thunderstorm that splits into two storms, which follow diverging paths (a left mover and a right mover). The left mover typically moves faster than the original storm, the right mover moves slower. Of the two, the left mover is more likely to weaken and dissipate (but on rare occasions can become a very severe anticyclonically-rotating storm), while the right mover is the one more likely to produce severe weather and retain a supercell structure.

SPLNS - Southern Plains

SPRD - spread

SQLN - see Squall Line

Squall - a strong wind characterized by a sudden onset in which the wind speed increases at least 16 knots (18 mph) and is sustained at 22 knots (25 mph) or more for at least 1 minute.

Squall Line (SQLN) - a line or narrow band of active thunderstorms

SRH - see Storm-Relative Helicity

SRN - southern

SS - see Sandstorm

SST - see Sea Surface Temperature

ST - see Stratus

Stable (STBL) - if a parcel is displaced (or moved), it will go right back to its original position and will not continue to rise.

Stable Boundary Layer - the stable and stratified layer that forms at the surface and grows upward, usually at night or in winter, as heat is extracted from the atmosphere’s base in response to longwave radiative heat loss from the ground. Stable boundary layers can also form when warm air is advected over a cold surface or over melting ice.

Stalled Front/System - a front or weather system that is moving very slowly or not at all. Sometimes the stalling of a front occurs because the two air masses involved have very similar temperature and moisture characteristics. If this happens or if weak winds are behind the original front, the front is not likely to move.

Standard Atmosphere - a hypothetical distribution with height of atmospheric temperature, pressure, and density

Standard Atmospheric Pressure - the pressure exerted by a 760 millimeter column of mercury at sea level at a temperature of 0 degrees Celsius; equal to 1013.25 millibars (mb), 29.92 inches of mercury (in of Hg), or 14.7 pounds per square inch

Stationary Front - the boundary between two air masses, neither of which is replacing the other--they’re at a stand-off.

Station Model - the specific pattern for entering meteorological symbols on a weather map. It describes the state of the weather at that geographical location

Station Pressure - the actual pressure measured at a given station location after being corrected for temperature, gravity, and instrument error

Statute Mile (SM) - a U.S. mile (5,280 feet)

STBL - see Stable

Stefan-Boltzmann Law - a mathematical relationship for electromagnetic radiation, which states that the irradiance of a blackbody is proportional to the fourth power of the absolute temperature of the blackbody

Stepped Leader - a faint, negatively charged channel that emerges from the base of a thunderstorm and moves toward the ground in a series of steps of about 1 microsecond duration and 50-100 meters in length, initiating a lightning stroke.

STFR - see Stratus Fractus

STG - strong

STJ - see Subtropical Jet

STLT - see Satellite

STM - see Stratiform

STN - station

STNRY - stationary

Stomata - microscopic openings on the underside of leaves. Water is lost through the stomata during transpiration.

Storm - a disturbance of the atmosphere marked by wind and usually by rain, snow, hail, sleet, or thunder and lightning

Storm Centroid - the computer- derived location of the center of a given storm. The NEXRAD RPG runs a storm detection and tracking algorithm to determine storm centroids automatically for each volume scan

Storm Prediction Center (SPC) - a national forecast center in Norman, Oklahoma, which is part of NCEP (one of nine centers); responsible for providing short-term forecast guidance for severe convection, excessive rainfall (flash flooding), and severe winter weather over the contiguous United States

Storm-Relative - measured relative to a moving thunderstorm, usually referring to winds, wind shear, or helicity

Storm-Relative Helicity (SRH) - a measure of shear

Storm-Relative Velocity - the wind velocity minus storm motion. The wind at a given location may be the combination of the environmental flow plus winds due to a thunderstorm. NEXRAD produces a storm-relative radial velocity product from the base velocity product by subtracting the average motion of all identified storms on the radar scope.

Storm-Scale - referring to weather systems with sizes on the order of individual thunderstorms

Storm Surge - an atypical rise of the sea along a shore, primarily resulting from the winds of a storm, especially those of a hurricane

Storm Top - the height of the top of the clouds. The higher the cloud top, the more likely it is that the cloud will become a thunderstorm.

Straight-Line Winds - generally, any winds that are not associated with rotation, used mainly to differentiate them from tornadic winds.

Stratified - the atmosphere is divided into distinct layers, each with different densities or temperatures. Stably stratified means that density decreases with height (e.g., cold, dense air is on the bottom).

Stratiform (STM, STRFM) - having extensive horizontal development, as opposed to the more vertical development characteristic of convection; stratiform precipitation, in general, is relatively continuous and uniform in intensity

Stratocumulus (SC) - a low-level cloud in the form of a gray and/or whitish flat layer or patch, which nearly always has dark parts and is non-fibrous. Elements often are arranged in rows, bands, or waves.

Stratopause - the layer between the Stratosphere and the Mesosphere, located at an altitude approximately between 50 and 55 km (around 31 to 34 miles above the ground).

Stratosphere - a layer above the Troposphere. This layer is where most of the ozone resides, so temperature increases with height (ozone absorbs ultraviolet radiation, warming this layer).

Stratus (ST) - a low-level cloud in the form of a gray layer with a rather uniform base; one example is fog.

Stratus Fractus (STFR) - lower in height and darker in color than cumulus fractus, this cloud also has a ragged, shredded appearance.

Streamer - a positively charged channel that emerges from the ground or from an object (e.g., top of a tree) and moves toward the sky, initiating a lightning stroke if it meets with a stepped leader.

STRFM - see Stratiform

Subgeostrophic - around a trough or low-pressure system, the wind speed is weaker than it would have been if it were blowing in a straight line.

Sublimation - the process of changing from a solid directly to vapor or gas

Subsidence - sinking (downward) motion in the atmosphere, usually over a broad area

Subtropical High - a semi-permanent high pressure region near 30 degrees latitude

Subtropical Jet (STJ) - this jet stream is usually found between 20° and 30° latitude at altitudes between 12 and 14 km.

Suction Vortex (sometimes Suction Spot) - a small but very intense vortex within a tornado circulation; much of the extreme damage associated with violent tornadoes is attributed to suction vortices.

SUF - sufficient

Summer - the period extending from the summer solstice, about 21 June, to the autumnal equinox, about 22 September

Summer Solstice - the solstice when the sun is highest in the sky; the first day of summer

Sundog - a colored luminous spot appearing approximately 22 degrees on either side of the sun and at the same elevation as the sun. See Parhelion.

Sun Pillar - a luminous streak of white or slightly reddened light extending vertically above and below the sun, most frequently observed near sunrise or sunset

Supercell (or Supercell Storm) - a violent thunderstorm that can produce hail and large tornadoes. It contains tilted updrafts and downdrafts that are nearly in balance, allowing it to maintain itself for several hours. Radar characteristics often (but not always) include a hook echo, bounded weak echo region (BWER), V-notch, mesocyclone, and sometimes a TVS. Visual characteristics often include a rain-free base (with or without a wall cloud), flanking line, overshooting top, and back-sheared anvil, all of which normally are observed in or near the right rear or southwest part of the storm.

Supercooled - a condition in which the temperature of water is below freezing (0ºC or 32ºF), but the state of matter is still liquid. The liquid water will not freeze until its molecules are aligned in a certain way--this alignment can be provided if the droplet comes into contact with ice nuclei. As soon as a supercooled liquid hits an object that is below freezing, it will freeze on contact with the object (e.g., freezing rain).

Supergeostrophic - around a ridge or high pressure system, the wind speed is stronger than it would have been if it were blowing in a straight line

Super Typhoon - a typhoon that has maximum sustained winds of 150 mph or greater.

SVR - severe

SVR - abbreviation for Severe Thunderstorm Warning (issued by NWS Weather Forecast Offices)

SVRL - several

SW - southwest

S/W - see Shortwave

S/WV - see Shortwave

SWEAT Index - see Severe Weather Threat Index

SWLY - southwesterly

SWPC - see Space Weather Prediction Center

SWRN - southwestern

SWWD - southwestward

SXN - section

Synoptic - relating to or displaying conditions as they exist simultaneously over a broad area

Synoptic Scale - the scale of the high and low pressure systems of the lower troposphere; generally considered to be 1000 to 2500 km in length

SYNS - synopsis

SYS - system