Weather Words - Sn-Sz
-- Sn-Sz --
Snow: (1) Solid precipitation in the form of ice crystals of feathery or needlelike structure. The crystals may fall singly, or a large number of them may be matted together in the form of snowflakes. (2) The solid form of water which grows while floating, rising or falling in the free air of the atmosphere. It often takes the form of beautiful crystals generally having a hexagonal pattern.
Snow accumulation: The actual depth of snow on the ground at any instant. This may be during a snowstorm in progress, or after any single storm or series of storms; also called snow depth.
Snow as an insulator: Fresh snow is an excellent insulator. Ten inches of fresh snow is approximately equal to a six-inch layer of fiberglass insulation with an insulation value of R-18. As snow settles and air spaces diminish, the insulating quality decreases.
Snow blindness: Impaired vision or temporary blindness caused by sunlight reflected from snow surfaces. The medical name is niphablepsia. Symptoms of snow blindness are a gritty sensation under the eyelids, excessive watering, double vision.
Snow climate: (also called polar climate, arctic climate) The climate of geographical polar regions, but especially the climate of polar regions which are too cold to support the growth of trees.
Snow concrete: Snow that has been compressed at low temperature and that sets as a tough substance of considerably greater strength than uncompressed snow.
Snow creep: The continuous but extremely slow downhill movement of a layer of snow on a hillside or other slope.
Snow crust: The crisp, firm, almost icy surface upon fallen snow, usually formed by the slight melting and refreezing of the snow surface. A snow crust is designated as breakable or unbreakable according to its ability to support a man on skis.
Snow crust: A crisp, firm outer surface upon snow. A snow crust is designated as breakable or unbreakable according to its ability to support a man on skis.
Snow, deaths from: Snow kills hundreds of people in the United States each year. The primary snow-related deaths are from traffic accidents, overexertion, and exposure, but deaths from avalanches have been steadily increasing.
Snow depth: The actual depth of snow on the ground at any instant. This may be during a snowstorm in progress, or after any single storm or series of storms. Also called snow accumulation.
Snow devil: A small rotating wind or whirlwind of brief duration (a few seconds) that picks up and carries loose snow several feet into the air; also called a "snowspout".
Snow eater: Warm, dry chinook winds that sweep down the east slopes of the Rocky Mountains in the winter -- winds that can cause the disappearance of up to a foot on snow in one day as a combined result of evaporation and melting.
Snow fence: An open, slatted board fence 3-10 feet high, placed about 50 feet upwind of a highway, used to disrupt wind flow so that wind-blown snow is deposited immediately downwind of the fence, leaving a clear, protected strip parallel to the fence and slightly farther downwind.
Snow flurries: Brief occurrences of very light snow characterized by sudden onset, short duration and quick cessation, and which produce little or no accumulation.
Snow garland: A rare and beautiful phenomenon in which snow is festooned from trees, fences, etc., in the form of ropes up to several feet long and several inches in diameter.
Snow level: The elevation in mountainous terrain below which precipitation falls as rain and above which precipitation falls as snow. The snow level changes from storm to storm and even during a single storm.
Snow line: A line of elevation above which snow accumulates, either temporarily (seasonal snow line) or perennially. The snow line rises from sea level in polar regions to about 21,000 feet in equatorial regions.
Snow roller: A rolled-up cylinder of snow common in hilly regions when moist, cohesive snow is rolled downhill by wind. Sizes range from an inch up to three feet in length and a foot in diameter.
Snow shed: A protective structure erected over railroad tracks to prevent snow accumulation on the tracks. It is used where plowing is difficult, as in deep cuts, or where snow slides are frequent.
Snow sky: A bright illumination, usually white (but it can be any color), on the underside of clouds at night, produced by the reflection of light from a snow-covered surface; also called snow blink.
Snow shower: Snow which is characterized by sudden onset, vigor, rapid change in intensity, short duration and quick cessation. The appearance of the sky changes quickly during showery weather.
Snow showers: Snow characterized by sudden onset, great vigor, rapid change in intensity, short duration and quick cessation. Significant accumulation can result.
Snowball: A mass of snow formed by pressing soft, wet snow together (usually with the hands), or by rolling snow together.
Snowbelt: Any area downwind of an inland lake or sea in which lake-effect snows result in significantly greater seasonal snowfall totals than in surrounding areas of the region.
Snowbow: A rainbow produced when sunlight is reflected and refracted by ice crystals in the air (just as a normal rainbow is produced by the reflection and refraction of sunlight by raindrops).
Snowburst: A brief, very intense shower of snow that greatly reduces visibility and produces rapid snow accumulation. Snowbursts usually occur in association with lake-effect snow produced by the Great Lakes.
Snowdrift: A mass or bank of snow piled up by the wind; also called a drift. Drifted snow is usually difficult to shovel or plow because of its great density.
Snowflake fall speed: The vast majority of snowflakes, perhaps 95 percent or more, fall at speeds of one to six feet per second, or 0.7 to 4.1 m.p.h. A snowflake's surface area and weight are the most important factors determining fall speed.
Snowflake size: Snowflakes, "packets" of falling snow formed when at least a few (and often many) individual ice crystals are matted together, can grow to huge size. The largest snowflakes are three to four inches in diameter. In extreme cases, ten-inch flakes have been reported.
Snowflakes: "Packets" of falling snow formed when at least a few (and often many) individual ice crystals are matted together. The largest snowflakes tend to occur when temperatures are near freezing. Most snowflakes fall at speeds of 0.7 to 4.1 m.p.h.
Snowfree months: In official Chicago snowfall records dating from 1885, July and August are the only two months of the year in which snow has never occurred. Traces of snow have fallen in June and September.
Snowiest city: Rochester, NY, receives an average of 94 inches of snow per year and is the snowiest major U.S. city (population 200,000 or more). Its annual municipal snow-removal budget (1995) is $3.7 million. Chicago's average annual snowfall is about 40 inches.
Snowpack: The total snow and ice on the ground, including new snow and all snow and ice still remaining from previous storms. The depth of Chicago's snowpack is measured daily at Midway Airport and recorded to the nearest inch.
Snowspout: A small rotating wind or whirlwind of brief (a few seconds) duration that picks up and carries loose snow several feet into the air; also called a snow devil.
Socked in: Colloquially descriptive of airport visibility so poor that the airport is effectively closed to aircraft operations. The term originated in the early days of aviation when dense fog hid the airport's wind sock (used to determine wind direction).
Soft day: In Ireland, an overcast, foggy, gray day with drizzle or misty rain but no heavy downpours.
Soil creep: The very slow downslope movement of surface soil or rock debris, usually imperceptible except to observations of long duration. Indications of this process are tree and post tilt.
Solar constant: (1) The total radiation energy received from the sun per unit of time per unit of area on a theoretical surface perpendicular to the sun's rays and at the Earth's average distance from the sun. The value of the solar constant is 12.77 calories per square inch per minute. (2) Solar constant: The amount of energy that the Earth receives from the sun on a surface perpendicular to the sun's rays; the value of the solar constant is 12.77 calories per square inch per minute.
Solar distance: The sun is eight light-minutes from the Earth (93
million miles). That means the sun we see "now" is actually what it looked like eight minutes ago.
Solar flare: The sudden release of magnetic energy from the sun's atmosphere, resulting in emission of radiation across the entire electromagnetic spectrum (including visible light). Radiation from a solar flare reaches the Earth in eight minutes.
Solar summer: The three-month period when day length is longest and solar radiation above the clouds is greatest. In the Northern Hemisphere solar summer is the period from about May 1 to August 1.
Solar winter: The three-month period when day length is shortest and solar radiation (above the clouds) is the least. In the Northern Hemisphere, approximately the period of November, December, January.
Sonic boom: A shock wave that is produced by an aircraft or other object flying at a speed equal to or exceeding the speed of sound and that is heard on the ground as a sound like a clap of thunder.
Sound: A pressure fluctuation in a gas (or liquid or solid) in the range of sonic frequencies that is detected by a suitable receiver (like a mechanical device or the human ear).
Sounding: A series of measurements of atmospheric variables (such as temperature, air pressure or winds) through a large vertical depth of the atmosphere.
South America's highest temperature: On Dec. 11, 1905, the temperature at Rivadavia, Argentina, soared to 120 degrees F, the highest temperature ever recorded on the continent of South America.
South America's lowest temperature: On June 1, 1907, the temperature at Sarmiento, Argentina, plunged to -29 degrees F, the lowest temperature ever recorded on the continent of South America. This value is close to Chicago's all-time lowest temperature, -27 degrees F (January 20, 1985).
South Pole's coldest month: July, 1997, with an average temperature of -87 degrees F for the month, as observed at the South Pole Station, Antarctica. The previous record cold month at that location was July, 1965, with an average temperature of -84 degrees F.
Southern lights: The aurora of the Southern Hemisphere (aurora australis), comparable to the northern lights (aurora borealis) of the Northern Hemisphere.
Spider lightning: Lightning that branches upward and outward along the sides and tops of large thunderstorms. The lightning seems to "crawl" across the sky, branching as it goes; also called "anvil crawlers."
Spiral bands: The characteristic arrangement of rain bands associated with hurricanes; they curve cyclonically (counterclockwise) inward toward the center of the storm.
Splash erosion: The spattering of small soil particles caused by the impact of raindrops on wet soils. The loosened and spattered particles may or may not be subsequently removed by surface runoff.
Spring: The season of the year comprising the transition period from winter to summer. (1) At Chicago spring is a time of decreasing cyclonic activity, rising temperatures, and increasingly frequent and strong thunderstorm activity. (2) At Chicago, spring is a time of rising temperatures and increasingly frequent and strong thunderstorm activity. Meteorological spring begins today and consists of March, April and May. Astronomical spring extends from the vernal equinox, March 20th this year, to the summer solstice, June 20th.
Sprinkle: A very light shower of rain lasting a few minutes or less; a shower so brief and light that it merely dampens but does not wet an exposed surface.
Sprite: A weak luminous emission that appears directly above a thunderstorm at the same time that a lightning flash occurs within the thunderhead.
Sputnik: The first artificial satellite to be launched into space. Its launch by the Union of Soviet Socialist Republics on October 4, 1957, marked the beginning of the space age.
Squall: A strong wind characterized by sudden onset, duration of the order of minutes, then rather sudden decrease. A squall must produce a wind speed of at least 18 m.p.h. for two minutes or longer.
Squall line: A line of thunderstorms sometimes several hundred miles in length, with individual thunderstorms strung out along the line. Squall lines in the United States are the world's strongest and most severe.
Stable: A state of the atmosphere in which vertical air motions are inhibited, usually resulting from an inversion (warm air overlying cool air).
Stable air: A layer of air or an air mass in which vertical air motions are inhibited, usually resulting from an inversion (warm air overlying cool air).
Stage: The elevation of the water surface in a river as measured by a gage with reference to an arbitrarily selected base. It is a common method of expressing stream flow where the height of the water surface is the important factor.
Standard atmosphere: A unit of air pressure that is equal to the average atmospheric pressure naturally existing at sea level on the Earth's surface; the pressure exerted by a column of mercury 29.9213 inches high.
Standard atmospheric pressure: The pressure exerted by the weight of air at sea level: 14.7 pounds per square inch, 29.92 inches of mercury, 760 millimeters of mercury, 1013.25 millibars or 101.3 kilopascals.
Stationary front: The relatively motionless transition zone between two air masses; winds blow approximately parallel to the stationary front, but in opposite directions on either side of the frontal boundary.
Statistics: Accumulations of numerical facts. The science of statistics develops methods for dealing with large quantities of numerical data, then representing their essential features with a small number of statements.
Steam fog: Fog formed when very cold air drifts over much warmer water. During the winter, it is most pronounced around sunrise, the usual time of the daily minimum temperature.
Steam fog: Fog formed when water vapor is added to air which is colder than the vapor's source; occurs mainly when cold air drifts across relatively warm water. It is most pronounced around sunrise, the usual time of the daily minimum temperature.
Steering: A term loosely used for any influence upon the direction of movement of a weather feature (low pressure system, air mass, thunderstorm, etc.) exerted by another aspect of the atmosphere. For example, upper-level winds are said to "steer" surface weather systems.
Stevenson screen: A shelter for thermometers, consisting of a wooden box painted white, with double louvered sides and mounted on a stand four feet above the ground.
Storm: Any disturbed state of the atmosphere, especially as it affects the Earth's surface, and strongly implying destructive or otherwise unpleasant weather.
Storm chaser: A person who positions himself in or near severe storms (especially thunderstorms and hurricanes) in order to observe, photograph and study them. For many, viewing tornadoes is a main goal.
Storm surge: (1) The rapid rise of the level of the sea as a hurricane makes landfall. The storm surge is the most damaging and most dangerous aspect of a hurricane. (2) An increase in the level of the sea above the level that prevails when there is no storm. Large surges occur with hurricanes, but minor surges occur with the passage of low pressure systems.
Storm track: The path followed by the center of a low pressure system over a given period of time, usually its lifetime (a few days).
Stormy: Colloquially descriptive of any disturbed state of the atmosphere, especially as it affects the Earth's surface, and implying unpleasant weather, and possibly dangerous or destructive conditions.
Stovepipe tornado: A colloquial term used by tornado chasers to describe a tornado with straight sides (as contrasted to a tornado with tapering sides); a tornado as wide at its base as it is at cloud level.
Stratiform: Referring to clouds having extensive horizontal development, as opposed to the vertical orientation of convective (cumulus) clouds. Stratiform clouds cover large areas (sometimes hundreds of miles) and the precipitation they produce is relatively continuous and uniform in intensity. Stratiform clouds predominate during the winter in climates like Chicago's.
Stratus: (1) A uniform and nearly featureless layer of low cloud, resembling fog but not resting on the ground. It is invariably gray in color. When broken up into irregular shreds, it is called fractostratus. (2) A uniform, gray and nearly featureless layer of low cloud, resembling fog but not resting on the ground. The base of a stratus cloud layer is occasionally only one or two hundred feet above the ground.
Stratus clouds: A uniform, gray and nearly featureless layer of low cloud, often less than 1,000 feet above the ground. When broken up into irregular shreds, it is called stratus fractus.
Stratus fractus clouds: A ragged, gray layer of low cloud, often less than 1,000 feet above the ground, and usually occurring during inclement winter weather; also called fractostratus.
Streamwood microburst: At 8:10 a.m. CDT on June 29, 1990, a powerful microburst lasting about 30 seconds blasted the 4B Industrial Park in northwest suburban Streamwood, injuring six people and killing one. Brief 150 m.p.h. winds caused $10 million damage to 25 stores and industrial buildings.
Strong tornado: A tornado with a wind speed of 113-206 m.p.h. F2 or F3 on the tornado F scale developed by Dr. T. Fujita of the University of Chicago. Of all tornado occurrences, about 35 percent are strong.
Subgelisol: Unfrozen ground beneath permafrost.
Subjective forecast: A weather forecast produced largely by methods involving the judgment and skill of a forecaster as opposed to an "objective forecast" produced by mathematical models of the atmosphere.
Sublimation: The process by which ice is converted directly into water vapor gas without going through the liquid state, or the reverse process by which water vapor gas is converted directly into ice without going through the liquid state.
Subsidence: A sinking or descending motion of air in the atmosphere, usually over a broad area (hundreds of miles) such as is associated with high pressure systems; also, the localized sinking of air that occurs in the vicinity of large thunderstorms.
Sultry: An oppressively uncomfortable state of the weather resulting from the simultaneous occurrence of high temperature, high humidity and (usually) calm air and a cloudy sky.
Summer: (1) The warmest season of the year. Astronomical summer extends from the summer solstice, June 21, to the autumnal equinox, Sept. 21. Meteorological summer consists of June, July and August. (2) The most dangerous season in the sense that the stress of summer heat kills more Americans than any other weather-related phenomenon. Urban elderly are most at risk.
Summer of 1816: Atmospheric dust pollution following the 1815 eruption of the volcano Tambora in the East Indies reduced Northern Hemisphere temperatures and produced a chilly summer in 1816 across southeast Canada and the eastern U.S.
Summer solstice: The point on the sun's annual path at which it is displaced farthest north (to the Tropic of Cancer) from the Earth's equator. The Northern Hemisphere summer solstice falls on June 21.
Summertime lag of seasons: The period of time between the longest day (which represents the time of maximum heat input from the sun--June 21) and the actual date of the average highest temperatures (in Chicago, about July 22). Chicago's lag of seasons: about one month.
Sun: The closest star to the Earth (at a distance of 93 million miles) and the source of virtually all the heat energy that warms the planet and powers our weather. (1) The sun's mass is 330,000 times that of the Earth and its radius is 109 times that of the Earth. (2) The sun subtends 1/2 degree in our sky, roughly the same as the moon. (3) It derives its energy from the fusion of hydrogen atoms into helium atoms. (4) At its core, the sun's density is 100 times that of water. (5) The sun, carrying the Earth along with it, is rotating around the galactic center at the incredible speed of 140 miles per second, and it takes the sun about 200 million years to make one complete rotation.
Sun pillar: A luminous streak of light, white or slightly reddened, extending above and below the sun, most frequently seen near sunrise or sunset.
Sun scald: A sunlight-caused injury to the stems of trees or other woody plants that results in local death of the plant tissue. (1) In winter, sun scald is caused by the great variation in temperature on the side of the tree that is exposed to the sun in cold weather. (2) In summer, sun scald is due to excessive action of the sun's rays.
Sunburn: (1) The skin's response to injury from ultraviolet radiation from the sun or artificial light sources. Cellular and DNA damage are a given when this occur. (2) A superficial inflammation of the skin caused by the sun's rays. A form of erythema that occurs when histamine is formed as the result of a photochemical reaction under the influence of ultraviolet radiation.
Sundogs: (1) Two bright spots of light at opposite sides of a circular halo around the sun. The halo results from the bending of the sun's rays as they pass through air filled with ice crystals creates the halo. At a point on each side of the sun, the crystals act as tiny mirrors, reflecting the sun and forming the brilliant sundog highlights on the halo. (2) Two bright spots of reflected light at opposite sides of a circular halo around the sun. The halo results from bending of sunlight as is shines through ice crystals in the atmosphere.
Sunny: The state of the daytime sky when there is a total absence of clouds, or when the presence of clouds is minimal and in no way dulls the sky or aspect of the day.
Sunrise: The phenomenon of the sun's daily appearance on the eastern horizon as a result of the Earth's rotation. The time of sunrise is defined as the instant when the upper limb of the sun appears on the sea-level horizon.
Sunset: The phenomenon of the sun's daily disappearance below the western horizon as a result of the Earth's rotation. The time of sunset is defined as the instant when the upper limb of the sun just disappears below the sea-level horizon.
Sunshine: Direct radiation from the sun, as opposed to the shading of a location by clouds or other obstructions.
Sunspot: A temporary disturbed area on the face of the sun, appearing darker because it is cooler than surrounding areas. Sunspots appear in approximate 11-year cycles.
Sunspot cycle: A cycle with an average length of 11.1 years, but varying between about 7 and 17 years, in the number and area of sunspots on the sun. Eleven-year cycles have been suggested for many kinds of weather events, but none of these has been conclusively substantiated.
Supercell thunderstorm: A huge, often severe, thunderstorm which persists for several hours because of an internal separation and balance between its updrafts and downdrafts. Thunderstorms normally last an hour or less.
Supercooled water: (1) Water that exists in the liquid state even though its temperature is below freezing (32 degrees F). This is a very common condition for tiny water droplets, and many clouds at sub-freezing temperatures contain supercooled droplets. (2) Water that stays in liquid form if undisturbed even though it has been cooled below its normal freezing point.
Superior air: An exceptionally dry mass of air formed when atmospheric processes force cold dry air aloft to sink to the earth's surface.
Supersaturation: A condition existing in air when its relative humidity exceeds 100 percent. It occurs when air that is saturated with water vapor and totally free of condensation nuclei is cooled.
Supersonic: Referring to an object moving faster than the speed of sound in the gas or liquid surrounding it.
Supplementary clouds: Portions of larger clouds which display special visual characteristics. Examples are incus, the anvil portion of cumulonimbus (thunderhead); mamma, the hanging protuberances, like udders, on the under surface of a cloud.
Surf: Waves occurring on a beach inshore of the point at which incoming waves break. Surf consists of waves that have broken and have air bubbles mixed in with the water.
Surge: An increase in the level of the sea above the level that prevails when there is no storm. Large surges occur with hurricanes, but minor surges occur with the passage of low pressure systems.
Surging glacier: A glacier experiencing a great increase in movement, 10 to 100 times faster than its usual rate. Glacial surge events last less than one year, occurring at intervals of 15 to 100 years.
Susurrus: The soft, whispering, murmuring or rustling sound of a gentle wind; more generally, a whisper or murmur.
Swell: Ocean waves that are no longer being built or supported by the wind. (1) Ocean waves that have traveled beyond the generating area. (2) Swell characteristically exhibits a longer and more regular period and has flatter wave crests than waves that are still being built by the wind.
Sweltering: An oppressively uncomfortable state of the weather resulting from the simultaneous occurrence of high temperatures and high humidity.
Sydney, Australia, hailstorm: On April 14, 1999 (a Wednesday) a severe thunderstorm lashed Sydney, Australia, for five hours, bringing hail 3.5 inches in diameter. Total damage in the city: $650 million.
Synoptic: Pertaining to an overall view. In meteorology, referring to the use of weather data obtained simultaneously over a wide area -- thousands of miles -- in order to present a comprehensive and instantaneous picture of the state of the atmosphere.
Synoptic scale: Of or relating to atmospheric phenomena ranging in size from a few hundred miles to about two thousand miles. An example of a synoptic scale event: a low pressure system.
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