Weather Words - Sa-Sm

-- Sa-Sm --

Safe room: A specially built tornado- or hurricane-resistant room in a house (or other building) designed with reinforced walls to provide occupants of the structure with safe shelter from severe storms.

Safe yield: The rate with which water can be indefinitely extracted from wells or diverted from surface water sources like lakes or reservoirs without causing depletion of the water supply.

Saffir-Simpson hurricane scale: A hurricane intensity scale that relates hurricane damage to wind speeds and central air pressures. Category 1: wind speeds 74-95 m.p.h; 2: 96-110 m.p.h; 3: 111-130 m.p.h.; 4: 131-155 m.p.h.; 5: over 155 m.p.h.

Sahara Desert: The Sahara Desert, stretching across the whole 3,200-mile span of north Africa, is the world's largest desert. Its 3.5 million square miles is almost as large as all 50 United States. Most of the Sahara's interior receives less than one inch of rain per year.

Saharan air layer (SAL): A mass of very dry, dusty air that originates over Africa's Sahara Desert during the late spring, summer and early autumn, and moves west and out over the tropical Atlantic Ocean. Its dryness inhibits hurricane formation over the ocean.

St. Elmo's Fire: The harmless luminous green or blue glow resulting from atmospheric electrical discharge sometimes seen on a ship's mast, on power lines, airplane wings, or just about any elevated objects.

St. Louis tornado: On Sept. 29, 1927, a tornado claimed the lives of 79 people as it slashed an 8-mile path across St. Louis, MO, to Granite City, Ill. The damage path was at times 1 1/4 miles wide.

St. Martin's summer: In English folklore, a period of fine, calm weather occurring in November. It is comparable to Indian Summer in the Midwest and New England areas of the United States.

St. Swithin's Day: In English folklore, July 15 is supposed to govern the weather on the following 40 days. Specifically, if it rains on St. Swithin's Day, it will continue to rain for 40 more days.

Saltiest ocean water: The surface waters of the North Atlantic Ocean have a higher salinity than those of any other ocean, with salinity values exceeding 37 parts per thousand in latitudes 20 degrees to 30 degrees N.

Sand haze: Reduced visibility caused by tiny suspended particles of sand and dust mixed into the air by wind, especially prevalent in desert regions where there is little moisture and vegetation.

Sand wall: The leading edge of a sharp wind increase (such as a thunderstorm gust front) that is filled with suspended sand and dust, and from a distance looks like an advancing knobby wall.

Sandstorm: A strong wind which carries sand through the air, but rarely raises the sand higher than 50 feet above ground. It usually occurs in desert regions, often among sand dunes.

Santa Ana: A hot, dry desert wind blowing from the east or northeast, especially in the pass and river Valley of Santa Ana, California. It blows, sometimes with great force, from the deserts to the east of the Sierra Nevada Mountains. 100 m.p.h. wind gusts have been recorded.

Saskatchewan screamer: A fast-moving winter low pressure system that sweeps from Saskatchewan, Canada, southeast into the Midwest. Screamers bring low water-content snow and, when intense, can produce blizzards.

Sastrugi: Sharp, irregular ridges formed on a snow surface by wind; the singular form of the word is "sastruga".

Satellite: Any natural or manmade object that orbits around a much larger astronomical body.

Saturated air: Experimentation has shown that a specific maximum amount of water vapor can be contained in air at a given temperature and air pressure, and air holding that maximum amount of moisture is said to be saturated.

Saturation: In meteorology, the state of the atmosphere in which air contains the maximum amount of water vapor that it can hold at a specific temperature and air pressure. At saturation: the relative humidity is 100 percent, temperature and dew point are equal, evaporation of water ceases.

Scattered cloudiness: Descriptive of an amount of cloudiness covering 10 to 50 percent of the sky, at least half of which is opaque. If less than half the cloud layer is opaque, the layer is called thin scattered.

Schaefer, Vincent Joseph: (1906-1993) U.S. chemist and meteorologist who initiated the modern era of cloud seeding and weather control when, on November 13, 1946, he released three pounds of dry ice (frozen carbon dioxide) pellets from an airplane into a cloud over Pittsfield, Mass., and streamers of snow began to fall from the cloud.

Scheele, Karl Wilhelm: (1742-1786) Swedish chemist and apothecary who isolated oxygen from various substances in 1772 (two years before Joseph Priestley, who is usually credited as the discoverer of oxygen).

Scintillation: Twinkling of the stars. More generally, scintillation is the rapid variation in apparent position, brightness or color of a distant luminous object when viewed through the Earth's atmosphere.

Scotch mist: A combination of dense fog, mist and heavy drizzle that occurs frequently in Scotland and in parts of England.

Scud: Unattached, ragged, low, gray clouds, usually stratus fractus, moving rapidly below a layer of higher clouds, and usually during inclement weather.

Sea: The collective and interconnected "world ocean" of salt water that occupies the Earth's depressions and covers the greater part of the Earth's surface.

Sea breeze: A coastal local wind that blows from sea to land, caused by the temperature difference when the sea surface is colder than the adjacent land. The Lake Michigan "lake breeze" is a sea breeze.

Sea level: The height of the ocean after averaging out variations due to waves. Sea levels rose about six inches in the 1900s. A further rise of 18 inches (three times greater) is possible in this century.

Sea level air pressure: 29.92 inches of mercury, the force exerted per unit area by the weight of the atmosphere at sea level; in other units: 1013.25 millibars, 14.7 pounds per square inch.

Season: A division of the year according to some regularly recurrent phenomena. In mid latitudes, seasons are based upon the annual cycle of temperature; in the tropics, seasons are often defined according to annual cycles of rain.

Seasonal affective disorder: A depressed, tired or irritable condition brought on by diminished sunlight, most common at higher latitudes during the winter when nights are long and days are frequently cloudy.

Seasonal drought: Drought which occurs in climates with distinct annual periods of very dry weather. The climate of coastal southern California brings seasonal drought (rainy winter, rain-free summer).

Seiche: (pronounced say-sh) In the Great Lakes region, any sudden rise in the water level on a coast or in a harbor of one of the Great Lakes. Seiches range in height from an inch or two to several feet.

September: The ninth month of the year and the beginning of meteorological autumn. With an average temperature of 64.4° and average precipitation of 3.82 inches, it is Chicago's 4th warmest and 2nd wettest month.

Settlement: The gradual decrease in thickness of a layer of snow from compaction due to gravity and a change in the ice crystal structure of the snow.

Severe storm: Any kind of storm that is destructive or life-threatening. The term is commonly applied to intense thunderstorms and to powerful winter storms, but also includes intense tropical storms like hurricanes.

Severe thunderstorm: A thunderstorm that produces one or more of the following phenomena: a tornado; winds of 50 knots (58 miles per hour) or greater; hail 3/4 inch in diameter or larger.

Severe weather: In general, any kind of destructive or life-threatening weather event. Thunderstorm phenomena that can be destructive and life-threatening are tornadoes, high winds, hail, excessive rainfall (and resultant flash flooding) and lightning.

Sferics (atmospherics): Radio-frequency electromagnetic radiations that originate mainly from thunderstorm lightning. Sferics are heard as the "static" in AM radios.

Shaw, Sir Napier: (1854-1945) British meteorologist who contributed to the development of modern meteorology. He introduced the millibar, a unit of air pressure in use today, and he first used lapse to describe the decrease of atmospheric temperature with height.

Sheet lightning: Diffuse illumination of those clouds that surround the path of a lightning bolt; not a unique form of lightning, only a manifestation of ordinary lightning in the presence of obscuring clouds.

Shelterbelt: Rows of trees and shrubs arranged and planted to break the wind, the purpose being to prevent soil erosion by wind and to protect people and livestock from cold winter winds.

Shore ice: Ice that is firmly attached to the shore of a lake or sea, or anchored on the sea bed. Pack ice drifts and freely moves with winds and water currents.

Short, medium, long-range forecasts: A short-range forecast consists of the first and second days; medium range is days three through seven; long range is considered to be eight days in the future, and beyond.

Showers: Precipitation characterized by sudden onset, rapid change in intensity, short duration and quick cessation. The appearance of the sky usually changes quickly during showery weather.

Siberian express: In the winter, upper winds that blow from Siberia north to the Arctic Ocean, then south across Canada into the United States, directing bitterly cold air into the United States.

Sidereal year: The time necessary for the Earth to make one complete revolution around the sun; 365 days, 6 hours 9 minutes, 9.5 seconds. The calendar year is 365 days, and 366 days every fourth year.

Signature: On a radar display, an identifying characteristic that enables the radar operator to determine the nature of the weather phenomenon being viewed (tornado signature, hail signature, etc.).

Silver frost: In Canada, a popular term for the deposit of glaze on trees and other exposed objects resulting from an occurrence of freezing rain or freezing drizzle; also called silver thaw.

Silver thaw: In Canada, a popular term for the deposit of glaze on trees and other exposed objects resulting from an occurrence of freezing rain or freezing drizzle; also called silver frost.

Singularity: A weather event that occurs around a certain date with a frequency of occurrence greater than chance would dictate. The "January thaw" is the only statistically provable singularity. Chicago temperatures show evidence of a "January thaw" from Jan. 20-22.

Sirocco: Hot, dusty winds that sweep from the deserts of north Africa across the Mediterranean Sea and reach Malta, Sicily and southern Italy as oppressively hot, humid, dusty south winds.

Ski: To glide or travel over snow by means of a pair of long, flat runners attached to the boots of the feet.

Skip: A phenomenon in which sound or radio energy may be detected only at various distance intervals from the energy source, as a result of the presence of an energy reflecting or refracting layer in the atmosphere.

Sky: The apparent hemispheric surface against which all aerial objects are seen from the Earth.

Slatch: A lull in a high windstorm; a momentary lull between breaking waves, favorable for launching a boat; in seamen's language, a period of transitory breezes, or an interval of fair weather.

Sleet: (1) Precipitation in the form of ice pellets formed when raindrops (or largely melted snowflakes) freeze as they fall through subfreezing air near the surface of the earth. (2) Precipitation in the form of small ice pellets. Sleet forms when raindrops, originating in warmer air aloft, fall through a layer of subfreezing air at ground level and then freeze on their way down.

SLOSH: Acronym for Sea, Lake and Overland Surges from Hurricanes, a computer model used by the National Hurricane Center to estimate storm surge heights and winds resulting from hurricanes.

Slush: Snow or ice on the ground that has been reduced to a soft, watery mixture by rain, warm temperatures or chemical treatment. Slush is often contaminated by oil, dirt and other debris.

Small craft advisory: Weather and/or sea conditions present or expected to occur within five miles of shore, characterized by sustained winds of 18-33 knots or waves four feet in height or greater.

Smallest raindrops: About 0.004 inch in diameter. When first formed, water droplets are about 0.0004 inch in diameter, and they float freely in the atmosphere. When they increase in size to about 0.004 inch in diameter, they become large enough to fall as raindrops.

Smog: Visible air pollution in urban areas. The word was coined in 1905 by Harold Des Veaux, a London physician, to describe natural fog contaminated by smoke. Today it is a synonym for general air pollution.

Smoke: Particulate matter in the atmosphere that results from combustion. When atmospheric smoke is present, it gives a very red color to the rising or setting sun and a reddish tinge to the overhead sun.

Smudging: A frost-preventive measure formerly employed in orchards. The technique involves the use of smoldering fires to generate dense smoke, thereby slowing radiational cooling and preventing frost formation.