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Baseflow In hydrologic terms, streamflow which results from precipitation that infiltrates into the soil and eventually moves through the soil to the stream channel. This is also referred to as ground water flow, or dry-weather flow. Basin An area having a common outlet for its surface runoff. Also called a "Drainage Basin. Basin Lag In hydrologic terms, the time it takes from the centroid of rainfall for the hydrograph to peak. Basin Recharge In hydrologic terms, rainfall that adds to the residual moisture of the basin in order to help recharge the water deficit.
Bathymetry The science of measuring depths of the oceans, lakes, seas, etc. BCKG Backing- A counterclockwise shift in wind direction for example, south winds shifting to the east. If there is no variation in density, the beam is considered to be filled. Usually that width where the power density is one-half that of the axis beam.
Half-Power or 3 dB point Bear's Cage [Slang], a region of storm-scale rotation, in a thunderstorm, which is wrapped in heavy precipitation.
The term reflects the danger involved in observing such an area visually, which must be done at close range in low visibility. Beaufort Scale The Beaufort wind scale is a system used to estimate and report wind speeds when no measuring apparatus is available. It was invented in the early 19th Century by Admiral Sir Francis Beaufort of the British Navy as a way to interpret winds from conditions at sea.
Since that time, the scale has been modernized for effects on land. Beaufort Force 0 - Wind less than 1 kt, Calm, Sea surface smooth and mirror-like. Smoke drift indicates wind direction, still wind vanes. Wind felt on face, leaves rustle, vanes begin to move. Beaufort Force 3 - Wind kt, Gentle Breeze, Large wavelets, crests begin to break, scattered whitecaps. Leaves and small twigs constantly moving, light flags extended.
Special Avalanche Warning Issued by the National Weather Service when avalanches are imminent or occurring in the mountains. This product will be updated more frequently when it is used during active weather. An easterly wave or tropical wave can develop into a tropical cyclone. Fetch length is related to the height of the wind-generated wave heights. These inversions form between sinking heated air and air below and they are characterized by temperature increase with height through the inversion, while above the inversion, the temperature cools almost dry adiabatically.
Dust, leaves, and loose paper lifted, small tree branches move. Beaufort Force 5 - Winds kt, Fresh Breeze, Moderate waves 4 -8 ft taking longer form, many whitecaps, some spray. Small trees in leaf begin to sway. Beaufort Force 6 - Winds kt, Strong Breeze, Larger waves 8 ft, whitecaps common, more spray. Larger tree branches moving, whistling in wires. Beaufort Force 7 - Winds kt, Near Gale, Sea heaps up, waves 13 ft, white foam streaks off breakers. Whole trees moving, resistance felt walking against wind.
Beaufort Force 8 - Winds kt Gale, Moderately high 13 ft waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks. Whole trees in motion, resistance felt walking against wind. Beaufort Force 9 - Winds kt, Strong Gale, High waves 20 ft , sea begins to roll, dense streaks of foam, spray may reduce visibility. Slight structural damage occurs, slate blows off roofs.
Beaufort Force 10 - Winds kt, Storm, Very high waves 20 ft with overhanging crests, sea white densely blown foam, heavy rolling, lowered visibility. Seldom experienced on land, trees broken or uprooted, "considerable structural damage". Beaufort Force 11 - Winds kt, Violent Storm, Exceptionally high 30 ft waves, foam patches cover sea, visibility more reduced. Beaver 's Tail [Slang], a particular type of inflow band with a relatively broad, flat appearance suggestive of a beaver's tail. It is attached to a supercell's general updraft and is oriented roughly parallel to the pseudo-warm front, i.
As with any inflow band, cloud elements move toward the updraft, i. Its size and shape change as the strength of the inflow changes. See also inflow stinger. Bed Load In hydrologic terms, sand, silt, gravel, or soil and rock detritus carried by a stream on or immediately above its bed. The particles of this material have a density or grain size such as to preclude movement far above or for a long distance out of contact with the stream bed under natural conditions of flow.
Beginning of Freezup In hydrologic terms, date on which ice forming a stable winter ice cover is first observed on the water surface Beginning of the Breakup In hydrologic terms, date of definite breaking, movement, or melting of ice cover or significant rise of water level. BM - In hydrologic terms, a permanent point whose known elevation is tied to a national network.
These points are created to serve as a point of reference. Benchmarks have generally been established by the USGS, but may have been established by other Federal or local agencies. Benchmarks can be found on USGS maps. Bergeron Process The process by which ice crystals in a cloud grow at the expense of supercooled liquid water droplets. Bergy Bit A piece of ice which has broken away from an iceberg, extending meters above the sea surface and square meters in area. Can also be the remains of a melting iceberg.
Bermuda High A semi-permanent, subtropical area of high pressure in the North Atlantic Ocean off the East Coast of North America that migrates east and west with varying central pressure. Depending on the season, it has different names. When it is displaced westward, during the Northern Hemispheric summer and fall, the center is located in the western North Atlantic, near Bermuda.
In the winter and early spring, it is primarily centered near the Azores in the eastern part of the North Atlantic. Also known as Azores High. Best Track A subjectively-smoothed representation of a tropical cyclone's location and intensity over its lifetime. The best track contains the cyclone's latitude, longitude, maximum sustained surface winds, and minimum sea-level pressure at 6-hourly intervals. Best track positions and intensities, which are based on a post-storm assessment of all available data, may differ from values contained in storm advisories.
They also generally will not reflect the erratic motion implied by connecting individual center fix positions. Billow Cloud A cloud consisting of broad parallel bands oriented perpendicular to the wind. BIN Radar sample volume. Specifically, the term most often refers to the planetary boundary layer, which is the layer within which the effects of friction are significant. For the earth, this layer is considered to be roughly the lowest one or two kilometers of the atmosphere. It is within this layer that temperatures are most strongly affected by daytime insolation and nighttime radiational cooling, and winds are affected by friction with the earth's surface.
The effects of friction die out gradually with height, so the "top" of this layer cannot be defined exactly. Slang reference to patchy ice on roadways or other transportation surfaces that cannot easily be seen. In hydrologic terms, transparent ice formed in rivers and lakes. Blackbody A hypothetical "body" that absorbs all of the electromagnetic radiation striking it - it does not reflect or transmit any of the incident radiation. A blackbody not only absorbs all wavelengths, but emits at all wavelengths with the maximum possible intensity for any given temperature. Blackbody Radiation The electromagnetic radiation emitted by an ideal blackbody adhering to the radiation laws; it is the theoretical maximum amount of electromagnetic radiation of all wavelengths that can be emitted by a body at a given temperature.
BLZD - A blizzard means that the following conditions are expected to prevail for a period of 3 hours or longer: These conditions are expected to prevail for a minimum of 3 hours. BLO Below Blocked Flow Flow approaching a mountain barrier that is too weak or too stable to be carried over the barrier. Blowing A descriptor used to amplify observed weather phenomena whenever the phenomena are raised to a height of 6 feet or more above the ground Blowing Dust or Sand Strong winds over dry ground, that has little or no vegetation, can lift particles of dust or sand into the air.
These airborne particles can reduce visibility, cause respiratory problems, and have an abrasive affect on machinery. Blowing Snow Blowing snow is wind-driven snow that reduces surface visibility. Blowing snow can be falling snow or snow that has already accumulated but is picked up and blown by strong winds. Blowing snow is usually accompanied by drifting snow. Blowing Snow Advisory Issued when wind driven snow reduces surface visibility, possibly, hampering traveling. Blowing snow may be falling snow, or snow that has already accumulated but is picked up and blown by strong winds.
Blue Watch or Blue Box [Slang], a severe thunderstorm watch. Blustery Same as Breezy ; 15 to 25 mph winds.
Bora A regional downslope wind whose source is so cold that it is experienced as a cold wind, despite compression warming as it descends the lee slope of a mountain range. Border Ice In hydrologic terms, an ice sheet in the form of a long border attached to the bank or shore. Boundary Layer In general, a layer of air adjacent to a bounding surface. Specifically, the term most often refers to the planetary boundary layer , which is the layer within which the effects of friction are significant. The effects of friction die out gradually with increasing height, so the "top" of this layer cannot be defined exactly.
There is a thin layer immediately above the earth's surface known as the surface boundary layer or simply the surface layer. This layer is only a portion of the planetary boundary layer, and represents the layer within which friction effects are more or less constant throughout as opposed to decreasing with height, as they do above it. The surface boundary layer is roughly 10 meters thick from the surface up to 10 m above the ground , but again the exact depth is indeterminate. Like friction, the effects of insolation and radiational cooling are strongest within this layer.
Radar signature within a thunderstorm characterized by a local minimum in radar reflectivity at low levels which extends upward into, and is surrounded by, higher reflectivities aloft. This feature is associated with a strong updraft and is almost always found in the inflow region of a thunderstorm. It cannot be seen visually. Damaging straight-line winds often occur near the "crest" or center of a bow echo. Areas of circulation also can develop at either end of a bow echo, which sometimes can lead to tornado formation - especially in the left usually northern end, where the circulation exhibits cyclonic rotation.
Bowen Ratio For any moist surface, the ratio of heat energy used for sensible heating conduction and convection to the heat energy used for latent heating evaporation of water or sublimation of snow. The Bowen ratio ranges from about 0. It is named for Ira S. Bowen , an American astrophysicist.
Box Model A computer model used to calculate air pollution concentrations. Shoaling The process whereby waves coming into shallow waters are slowed by bottom friction and become closer together and steeper. Shore Ice An ice sheet in the form of a long border attached to the bank or shore. Short-fuse warnings include tornado warnings, severe thunderstorm warnings, and flash flood warnings. Tornado and severe thunderstorm warnings typically are issued for periods of an hour or less, flash flood warnings typically for three hours or less.
Short Term Forecast This National Weather Service narrative summary describes the weather in the local area and includes a short-range forecast usually not more than 6 hours. This product will be updated more frequently when it is used during active weather. This product is also sometimes referred to as a nowcast.
Shortwave or Shortwave Trough A disturbance in the mid or upper part of the atmosphere which induces upward motion ahead of it. If other conditions are favorable, the upward motion can contribute to thunderstorm development ahead of a shortwave. Sidelobe A secondary energy maximum located outside the main radar beam. Typically, it contains a small percentage of energy compared to the main lobe, but it may produce erroneous echoes. Side Channel Spillway A spillway whose crest is roughly parallel to the channel immediately downstream of the spillway.
Significant Wave Height The average height trough to crest distance of the one-third highest waves. An experienced observer will most frequently report heights equivalent to the average of the highest one-third of all waves observed. Single Cell Thunderstorm This type of thunderstorm develops in weak vertical wind shear environments.
Siphon Spillway A spillway with one or more siphons built at crest level. This type of spillway is sometimes used for providing automatic surface-level regulation within narrow limits or when considerable discharge capacity is necessary within a short period of time.
Site-Specific Term used in conjunction with "forecast" or "warning" to convey the fact that a hydrologic stream forecast is produced for an individual stream gage location as opposed to a general area e. These grains usually bounce upon impact with the ground or pavement. Slight Chance A National Weather Service precipitation descriptor for a 20 percent chance of measurable precipitation 0.
When the precipitation is convective in nature, the term widely scattered is used. See Precipitation Probability PoP. Slight Risk of Severe Thunderstorms An area of organized severe storms, which is not widespread in coverage with varying levels of intensity. See high risk , moderate risk , enhanced risk and marginal risk. Sling psychrometer A psychrometer in which the wet and dry bulb thermometers are mounted upon a frame connected to a handle. The psychrometer may be whirled by hand in order to provided the necessary ventilation.
Small Craft Advisory This is issued by the National Weather Service to alert small boats to sustained more than 2 hours hazardous weather or sea conditions. Small Stream Flooding Flooding of small creeks, streams, or runs.
Smog Originally smog meant a mixture of smoke and fog. Now, it means air that has restricted visibility due to pollution or pollution formed in the presence of sunlight--photochemical smog. Smoke FU A suspension in the air of small particles produced by combustion. Smoke Management Conducting a prescribed fire or slash burn with firing techniques and meteorological conditions that keep the smoke's impact on the environment with acceptable limits. Snow Advisory This product is issued by the National Weather Service when a low pressure system produces snow that may cause significant inconveniences, but do not meet warning criteria and if caution is not exercised could lead to life threatening situations.
The advisory criteria varies from area to area. Snow and Blowing Snow Advisory This product is issued by the National Weather Service during situations that cause significant inconveniences, but do not meet warning criteria and if caution is not exercised could lead to life threatening situations. The warning criteria in this definition varies from area to area.
Snow Core A sample of either freshly fallen snow, or the combined old and new snow on the ground. This is obtained by pushing a cylinder down through the snow layer and extracting it. Snow Density The mass of snow per unit volume which is equal to the water content of the snow divided by its depth. Snow Depth The combined total depth of both the old and new snow on the ground.
Snow Flurries They are intermittent light snowfalls of short duration generally light snow showers with no measurable accumulation. Snow Grains SG Precipitation of very small, white, and opaque grains of ice. They can be distinguished from ice pellets , because ice pellets bounce and snow grains do not bounce at all. Snow Pack The combined layers of snow and ice on the ground at any one time. It is also called snowcover. Snow Pillow An instrument used to measure snow water equivalents.
Snow pillows typically have flat stainless steel surface areas. The pillow below this flat surface is filled with antifreeze solution and the pressure in the pillow is related to the water-equivalent depth of the snow on the platform. One great advantage of snow pillows over a snow survey is the frequency of observations, which can be as high as twice per day. Snow Pellets GS Precipitation of white, opaque grains of ice. The grains are round or sometimes conical. Diameters range from about 0. Some accumulation is possible.
They are accompanied by strong, gusty surface winds, and possibly lightning generally moderate to heavy snow showers. Snow accumulations may be significant. Snow Stick A portable rod used to measure snow depth. Snow Water Equivalent The water content obtained from melting accumulated snow. Snowboard A flat, solid, white material, such as painted plywood, approximately two feet square, which is laid on the ground, or snow surface by weather observers to obtain more accurate measurements of snowfall and water content.
Snowmelt Flooding Flooding caused primarily by the melting of snow. Snowpack The total snow and ice on the ground, including both the new snow and the previous snow and ice which has not melted. Soil Moisture Water contained in the upper part of the soil mantle. This moisture evaporates from the soil and is the used and transpired by vegetation. Sounding A plot of the vertical profile of temperature and dew point and often winds above a fixed location.
Soundings are used extensively in severe weather forecasting, e. Southern Oscillation SO A "see-saw" in surface pressure in the tropical Pacific characterized by simultaneously opposite sea level pressure anomalies at Tahiti, in the eastern tropical Pacific and Darwin, on the northwest coast of Australia. Space Weather Prediction Center SWPC This center provides real-time monitoring and forecasting of solar and geophysical events, conducts research in solar-terrestrial physics, and develops techniques for forecasting solar and geophysical disturbances.
It also provides guidance on other short-term mesoscale phenomenon that may be of significance for example heavy snow potential, the formation of dense fog, etc. Spearhead Echo A radar echo associated with a Down burst with a pointed appendage extending toward the direction of the echo motion. The appendage moves much faster than the parent echo, which is drawn into the appendage. During its mature stage, the appendage turns into a major echo and the parent echo loses its identity. Special Avalanche Warning Issued by the National Weather Service when avalanches are imminent or occurring in the mountains.
It is usually issued for a 24 hour period. Special Fire Weather Meteorological services uniquely required by user agencies which cannot be provided at an NWS office during normal working hours. Examples are on-site support, weather observer training, and participation in user agency training activities.
Special Marine Warning SMW This is issued by the National Weather Service for hazardous weather conditions thunderstorms over water, thunderstorms that will move over water, cold air funnels over water, or waterspouts usually of short duration 2 hours or less and producing sustained winds or frequent gusts of 34 knots or more that is not covered by existing marine warnings.
This statement focuses on the major threat s of the disturbance, such as the potential for torrential rainfall on an island or inland area. The statement is coordinated with the appropriate forecast office s. Special Weather Statement SPS This is used by the National Weather Service to provide additional information about expected or ongoing significant weather changes not covered in other statements. This would include non-severe convective, winter weather, and non-precipitation events. Specific Humidity In a system of moist air, the ratio of the mass of water vapor to the total mass of the system.
Spectrum Width Cross Section SCS This WSRD radar product displays a vertical cross section of spectrum width on a grid with heights up to 70, feet 21 kilometers on the vertical axis and distance up to nm km on the horizontal axis. It is used to: Speed Shear The component of wind shear which is due to a change in wind speed with height, e. Speed shear is an important factor in severe weather development, especially in the middle and upper levels of the atmosphere. Spillway A structure over or through which excess or flood flows are discharged.
If the flow is controlled by gates, it is a controlled spillway, if the elevation of the spillway crest is the only control, it is an uncontrolled spillway. Some various types of spillways include: Auxiliary or Emergency Spillway - A secondary spillway designed to operate only during exceptionally large flood flows. Allows inflows from large storms to be released from the reservoir before the water level raises high enough to overtop the dam.
Fuse Plug Spillway - An auxiliary or emergency spillway comprising a low embankment or a natural saddle designed to be overtopped and eroded away during flood flows. Primary or Principal Spillway - The spillway which would be used first during normal inflow and flood flows. Shaft or Morning Glory Spillway - A vertical or inclined shaft into which flood water spills and then is conducted through, under, or around a dam by means of a conduit or tunnel. If the upper part of the shaft is splayed out and terminates in a circular horizontal weir, it is termed a "bellmouth" or "morning glory" spillway.
Spillway Crest The elevation of the highest point of a spillway. Spin-up Slang for a small-scale vortex initiation, such as what may be seen when a gustnado, landspout, or suction vortex forms. Splitting Storm A thunderstorm which 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, slower. Of the two, the left mover is most likely to weaken and dissipate but on rare occasions can become a very severe anticyclonic-rotating storm , while the right mover is the one most likely to reach supercell status.
They are issued upon request of User Agencies for wildfires, prescribed burns, or special projects. Spray PY An ensemble of water droplets torn by the wind from the surface of the of an extensive body of water, generally from crests of waves, and carried a short distance into the air. Spring An issue of water from the earth; a natural fountain; a source of a reservoir of water.
Spring Tide A tide higher than normal which occurs around the time of the new and full moon. Squall SQ A strong wind characterized by a sudden onset in which the wind speed increases at least 16 knots and is sustained more than 22 knots or more for at least one minute. Squall Line A line or narrow band of active thunderstorms. The line may extend across several hundred miles.
It forms along and ahead of an advancing cold front. Stability Index The overall stability or instability of a sounding is sometimes conveniently expressed in the form of a single numerical value. Used alone, it can be quite misleading, and at times, is apt to be worthless. The greatest value of an index lies in alerting the forecaster to those soundings which should be examined more closely.
Stable An atmospheric state with warm air above cold air which inhibits the vertical movement of air. Stable Air Air with little or no tendency to rise, that is usually accompanied by clear dry weather. Staccato Lightning A Cloud to Ground CG lightning discharge which appears as a single very bright, short-duration stroke, often with considerable branching. Staff Gage A vertical staff graduated in appropriate units which is placed so that a portion of the gage is in the water at all times.
Observers read the river stage off the staff gage. Stage The level of the water surface above a given datum at a given location along a river or stream. Stair Stepping The process of continually updating river forecasts for the purpose of incorporating the effects rain that has fallen since the previous forecast was prepared. The goal of using QPF is to minimize "stair-stepping. It gives the current weather condition in one word cloudy, rain, snow, fog, etc.
Station Identifier A group of four alphabetic characters used to identify a location that makes weather observations. Station Pressure The pressure that is read from a barometer but is not adjusted to sea level. Stationary Front A front that barely moves with winds blowing in almost parallel, but in opposite directions on each side of the front. Occasionally, these fronts can cause widespread flooding, because showers and thunderstorms moving along them will continue to move across the same area. This weather situation is called "train echoing". Steam Fog It forms as cold air moves over warm water.
Steering Winds or Steering Currents A prevailing synoptic scale flow which governs the movement of smaller features embedded within it. Stepped Leader A leader which initiates the very first stroke and establishes the channel for all subsequent streamers of a lightning discharge. Stilling Basin A basin constructed to dissipate the energy of fast-flowing water e.
Stoplogs Large logs, timbers or steel beams placed on top of each other with their ends held in guides on each side of a channel or conduit providing a temporary closure versus a permanent bulkhead gate. Storm Any disturbed state of the atmosphere, especially affecting the Earth's surface, and strongly implying destructive and otherwise unpleasant weather. Storms range in scale from tornadoes and thunderstorms through tropical cyclones to widespread extratropical cyclones. Reports contain information on storm paths, deaths, injuries, and property damage. The December issue includes annual tornado, lightning, flash flood, and tropical cyclone summaries.
Storm Hydrograph A hydrograph representing the flow or discharge of water past a point on a river. Storm Motion The speed and direction at which a thunderstorm travels. The SPC is 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. It is available for every elevation angle sampled. It is used to aid in displaying shear and rotation in storms and storm top divergence that might otherwise be obscured by the storm's motion, investigate the 3-D velocity structure of a storm, and help with determining rotational features in fast and uniform moving storms.
Storm Relative Mean Radial Velocity Region SRR This WSRD radar product depicts a 27 nm by 27 nm 50 km by 50 km region of storm relative mean radial velocity centered on a point which the operator can specify anywhere within a nm km radius of the radar. Storm Scale Referring to weather systems with sizes on the order of individual thunderstorms. See synoptic scale and mesoscale. Storm Tide The actual sea level resulting from astronomical tide combined with the storm surge.
This term is used interchangeably with "hurricane tide". Storm Track The path that a low pressure area follows. Straight-Line Hodograph The 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. This shape of hodograph favors multicell thunderstorms. Straight Line Winds Generally, any wind that is not associated with rotation, used mainly to differentiate them from tornadic winds. Stratiform Descriptive of clouds of extensive horizontal development, as contrasted to the more narrow and vertically developed cumuliform type. Stratiform clouds cover large areas but show relatively little vertical development. Stratiform precipitation, in general, is relatively continuous and uniform in intensity i.
Stratiform Rain Horizontally widespread rain, uniform in character, typically associated with macroscale fronts and pressure systems. Stratiform Rings and Bands These occur between the active convective bands of a hurricane outside of the eye wall. Stratiform Snow Same as for stratiform rain except precipitation is in the form of snow.
Stratocumulus Sc It has globular masses or rolls unlike the flat, sometimes definite, base of stratus. Stratosphere The layer of the atmosphere above the troposphere, where temperature increases with height. Stratus St It is a low, uniform sheet-like cloud. Stratus may appear in the form of ragged patches, but otherwise does not exhibit individual cloud elements as do cumulus and stratocumulus clouds. It usually is located between the ground and 6, feet meters.
It usually consist of mainly water vapor. Fog is a stratus cloud with its base located at the ground. Stream Gage A site along a stream where the stage water level is read either by eye or measured with recording equipment. Streamer A channel of very high ion density which propagates through the air by the continual establishment of an electron avalanche ahead of its tip. Streamflow Water flowing in the stream channel. It is often used interchangeably with discharge.
Striations Grooves or channels in cloud formations, arranged parallel to the flow of air and therefore depicting the airflow relative to the parent cloud. Striations often reveal the presence of rotation, as in the barber pole or "corkscrew" effect often observed with the rotating updraft of an Low Precipitation LP storm.
Sublimation The change from ice a solid directly to water vapor a gas without going through the liquid water phase. It is the opposite of Deposition. Subrefraction The bending of the radar beam in the vertical which is less than under standard refractive conditions. This causes the beam to be higher than indicated, and lead to the underestimation of cloud heights.
The slow sinking of air usually associated with high pressure areas. It is usually over a broad area. Sinking down of part of the earth's crust due to underground excavation, such as the removal of groundwater. These inversions form between sinking heated air and air below and they are characterized by temperature increase with height through the inversion, while above the inversion, the temperature cools almost dry adiabatically. The dew point temperature, relative humidity , and mixing ratio values all decrease with height through the inversion.
Subsurface Storm Flow The lateral motion of water through the upper layers until it enters a stream channel. This usually takes longer to reach stream channels than runoff. This also called interflow. Substation A location where observations are taken or other services are furnished by people not located at NWS offices who do not need to be certified to take observations. Sub-Synoptic Low Essentially the same as mesolow.
Subtropical Cyclone A low pressure system that develops over subtropical waters that initially has a non-tropical circulation, but in which some elements of tropical cyclone cloud structure are present. Subtropical cyclones can evolve into tropical cyclones. Subtropical cyclones are generally of two types: Cold Low Type - This type has a circulation extending from the surface to the upper troposphere, with the maximum sustained low-level winds typically extending to a radius of miles or more from the center.
Subtropical Depression A subtropical cyclone in which the maximum sustained surface wind speed using the U. Subtropical Storm A subtropical cyclone in which the maximum sustained surface wind speed using the U. Suction Vortex sometimes Suction Spot A small but very intense vortex within a tornado circulation. Several suction vortices typically are present in a multiple-vortex tornado. Much of the extreme damage associated with violent tornadoes F4 and F5 on the Fujita scale is attributed to suction vortices.
Supercell A thunderstorm with a persistent rotating updraft. Important in the formation of graupel and hail. Superrefraction Bending of the radar beam in the vertical which is greater than sub-standard refractive conditions. This causes the beam to be lower than indicated, and often results in extensive ground clutter as well as an overestimation of cloud top heights.
Surcharge Capacity The 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 normal full-pool elevation of the reservoir with the crest gates in the normal closed position. Surface Based Convection Convection occurring within a surface-based layer, i.
Compare with elevated convection. Surface Impoundment An indented area in the land's surface, such as a pit, pond, or lagoon. Surface Pressure The pressure that is read from a barometer but is not adjusted to sea level. Rain that falls on the stream channel is often lumped with this quantity. Surface Water Water that flows in streams and rivers and in natural lakes, in wetlands, and in reservoirs constructed by humans.
Sustained Wind Wind speed determined by averaging observed values over a 2-minute period. Sunny When there are no opaque not transparent clouds.
Surge A rise in water level caused by strong wind or fluctuations in the atmospheric pressure. This term is usually applied to a sharp set-up effect at the downwind end of the lake, but thunderstorms can cause brief local storm surges in bays and harbours. Sustained Overdraft Long-term withdrawal from the aquifer of more water than is being recharged.