ACCAS(usually pronounced ACK-kis) - AltoCumulus CAStellanus; mid-level clouds (bases generally 8 to 15 thousand feet), of which at least a fraction of their upper parts show cumulus-type development. These clouds often are taller than they are wide, giving them a turret-shaped appearance. ACCAS clouds are a sign of instability aloft, and may precede the rapid development of thunderstorms.Active Storage CapacityIn hydrologic terms, the total amount of reservoir capacity normally available for release from a reservoir below the maximum storage level. It is total or reservoir capacity minus inactive storage capacity. More specifically, it is the volume of water between the outlet works and the spillway crest. Area Forecast DiscussionThis National Weather Service product is intended to provide a well-reasoned discussion of the meteorological thinking which went into the preparation of the Zone Forecast Product. The forecaster will try to focus on the most particular challenges of the forecast. The text will be written in plain language or in proper contractions. At the end of the discussion, there will be a list of all advisories, non-convective watches, and non-convective warnings. The term non-convective refers to weather that is not caused by thunderstorms. An intermediate Area Forecast Discussion will be issued when either significant forecast updates are being made or if interesting weather is expected to occur.Area-Capacity CurveIn hydrologic terms, a graph showing the relation between the surface area of the water in a reservoir, the corresponding volume, and elevation. Astronomical DawnThe time at which the sun is 18 degrees below the horizon in the morning. Astronomical dawn is that point in time at which the sun starts lightening the sky. Prior to this time during the morning, the sky is completely dark.Astronomical DuskThis is the time at which the sun is 18 degrees below the horizon in the evening. At this time the sun no longer illuminates the sky.Astronomical Unit(abbrev. AU)- The mean earth-sun distance, equal to 1.496x1013 cm, or 214.94 solar radii.BackscatterThe portion of power scattered back in the incident direction.Bear's Cage[Slang], a region of storm-scale rotation, in a thunderstorm, which is wrapped in heavy
precipitation. This area often coincides with a radar hook echo and/or mesocyclone, especially one
associated with an HP storm.
The term reflects the danger involved in observing such an area visually, which must be done at close range
in low visibility.Beaufort ScaleThe 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 rises vertically.
Beaufort Force 1 - Wind 1-3 kt, Light Air, Scaly ripples, no foam crests. Smoke drift indicates wind direction, still wind vanes.
Beaufort Force 2 - Wind 4-6 kt, Light Breeze, Small wavelets, crests glassy, no breaking waves. Wind felt on face, leaves rustle, vanes begin to move.
Beaufort Force 3 - Wind 7-10 kt, Gentle Breeze, Large wavelets, crests begin to break, scattered whitecaps. Leaves and small twigs constantly moving, light flags extended.
Beaufort Force 4 - Winds 11-16 kt, Moderate Breeze, Small waves 1 -4 ft. becoming longer, numerous whitecaps. Dust, leaves, and loose paper lifted, small tree branches move.
Beaufort Force 5 - Winds 17-21 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 22-27 kt, Strong Breeze, Larger waves 8 -13 ft, whitecaps common, more spray. Larger tree branches moving, whistling in wires.
Beaufort Force 7 - Winds 28-33 kt, Near Gale, Sea heaps up, waves 13 -20 ft, white foam streaks off breakers. Whole trees moving, resistance felt walking against wind.
Beaufort Force 8 - Winds 34-40 kt Gale, Moderately high (13 -20 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 41-47 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 48-55 kt, Storm, Very high waves (20 -30 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 56-63 kt, Violent Storm, Exceptionally high (30 -45 ft) waves, foam patches cover sea, visibility more reduced.
Beaufort Force 12 -Winds 64+ kt, Hurricane, Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced.
CACloud-to-Air lightning.CAACold Air AdvectionCADCold Air Damming. The phenomenon in which a low-level cold air mass is trapped topographically. Often, this cold air is entrenched on the east side of mountainous terrain. Cold Air Damming often implies that the trapped cold air mass is influencing the dynamics of the overlying air mass, e.g. in an overrunning scenario.
Effects on the weather may include cold temperatures, freezing precipitation, and extensive cloud coverCADASCentralized Automated Data Acquisition System - a system of two minicomputers in NWSH.CalibrationIn hydrologic terms, the process of using historical data to estimate parameters in a hydrologic forecast technique such as SACSMA, routings, and unit hydrographs.CalmA weather condition when no air motion (wind) is detected.Canyon WindA foehn wind that is channeled through a canyon as it descends the lee side of a mountain barrier.Cap(also called "Lid") A layer of relatively warm air aloft, usually several thousand feet above the ground, which suppresses or delays the development of thunderstorms. Air parcels rising into this layer become cooler than the surrounding air, which inhibits their ability to rise further and produce thunderstorms. As such, the cap often prevents or delays thunderstorm development even in the presence of extreme instability. However, if the cap is removed or weakened, then explosive thunderstorm development can occur.
The cap is an important ingredient in most severe thunderstorm episodes, as it serves to separate warm, moist air below and cooler, drier air above. With the cap in place, air below it can continue to warm and/or moisten, thus increasing the amount of potential instability. Or, air above it can cool, which also increases potential instability. But without a cap, either process (warming/moistening at low levels or cooling aloft) results in a faster release of available instability - often before instability levels become large enough to support severe weather development.Cap CloudA stationary cloud directly above an isolated mountain peak, with cloud base below the elevation of the peak.CAPEConvective Available Potential Energy. A measure of the amount of energy available for convection. CAPE is directly related to the maximum potential vertical speed within an updraft; thus, higher values indicate greater potential for severe weather. Observed values in thunderstorm environments often may exceed 1000 joules per kilogram (J/kg), and in extreme cases may exceed 5000 J/kg.
However, as with other indices or indicators, there are no threshold values above which severe weather becomes imminent. CAPE is represented on an upper air sounding by the area enclosed between the environmental temperature profile and the path of a rising air parcel, over the layer within which the latter is warmer than the former. (This area often is called positive area.) See also CIN.CapillarityIn hydrologic terms,
1.The degree to which a material or object containing minute openings or passages, when immersed in a liquid, will draw the surface of the liquid above the hydrostatic level. Unless otherwise defined, the liquid is generally assumed to be water.
2. The phenomenon by which water is held in interstices above the normal hydrostatic level, due to attraction between water molecules. Capillary FringeIn hydrologic terms, the soil area just above the water table where water can rise up slightly through the cohesive force of capillary action. This layer ranges in depth from a couple of inches, to a few feet, and it depends on the pore sizes of the materials. The capillary fringe is also called the capillary zone.Capillary WavesWaves caused by the initial wind stress on the water surface causes what are known as capillary waves. These have a wavelength of less than 1.73 cm, and the force that tries to restore them to equilibrium is the cohesion of the individual molecules. Capillary waves are important in starting the process of energy transfer from the air to the water. Capillary ZoneUsed interchangably with Capillary Fringe; the soil area just above the water table where water can rise up slightly through the cohesive force of capillary action. This layer ranges in depth from a couple of inches, to a few feet, and it depends on the pore sizes of the materials.CappingA region of negative buoyancy below an existing level of free convection (LFC) where energy must be supplied to the parcel to maintain its ascent.
This tends to inhibit the development of convection until some physical mechanism can lift a parcel to its LFC. The intensity of the cap is measured by its convective inhibition. The term capping inversion is sometimes used, but an inversion is not necessary for the conditions producing convective inhibition to exist.Capping InversionAlternate term for Cap; a layer of relatively warm air aloft, usually several thousand feet above the ground, which suppresses or delays the development of thunderstorms. Air parcels rising into this layer become cooler than the surrounding air, which inhibits their ability to rise further and produce thunderstorms. As such, the cap often prevents or delays thunderstorm development even in the presence of extreme instability. However, if the cap is removed or weakened, then explosive thunderstorm development can occur.
The cap is an important ingredient in most severe thunderstorm episodes, as it serves to separate warm, moist air below and cooler, drier air above. With the cap in place, air below it can continue to warm and/or moisten, thus increasing the amount of potential instability. Or, air above it can cool, which also increases potential instability. But without a cap, either process (warming/moistening at low levels or cooling aloft) results in a faster release of available instability - often before instability levels become large enough to support severe weather development.CAPSCenter for Analysis and Prediction of StormsCarbon DioxideCO2; a colorless and odorless gas which is the fourth most abundant constituent of dry air.Carrington LongitudeA system of fixed longitudes rotating with the sunCatalina EddyA Catalina Eddy (coastal eddy) forms when upper level large-scale flow off Point Conception interacts with the complex topography of the Southern California coastline. As a result, a counter clockwise circulating low pressure area forms with its center in the vicinity of Catalina Island. This formation is accompanied by a southerly shift in coastal winds, a rapid increase in the depth of the marine layer, and a thickening of the coastal stratus. Predominately these eddies occur between April and September with a peak in June. A typical Catalina eddy will allow coastal low clouds and fog to persist into the afternoon. A strong Catalina eddy may extend to 6000 feet and these clouds will move through the inland valleys and reach as far as Palmdale.Catchment AreaIn hydrologic terms, an area having a common outlet for its surface runoff (also see Drainage Area or Basin, Watershed).CategoricalA National Weather Service precipitation descriptor for a 80, 90, or 100 percent chance of measurable precipitation (0.01 inch). See Precipitation Probability (PoP)Caution StageThe stage which, when reached by a rising stream, represents the level where appropriate officials (e.g., county sheriff, civil defense officials, or bypass gate operators) are notified of the threat of possible flooding. Alert stage or caution stage are used instead of caution stage in some parts of the country.CAVUClear or Scattered Clouds (visibility greater than 10 mi.)Chlorofluorocarbons(CFCs) - Manufactured substances used as coolants and computer-chip cleaners. When these products break down they destroy stratospheric ozone, creating the Antarctic Ozone Hole in the Southern Hemisphere spring (Northern Hemisphere autumn). While no longer in use, their long lifetime will lead to a very slow removal from the atmosphere.Climatological OutlookAn outlook based upon climatological statistics for a region, abbreviated as CL on seasonal outlook maps. CL indicates that the climate outlook has an equal chance of being above normal, normal, or below normal.Coastal Waters Forecast (CWF)The marine forecast for areas, including bays, harbors, and sounds, from a line approximating the mean high water mark (average height of high water over a 19-year period) along the mainland or near shore islands extending out to as much as 100 NM.
Cold Air Damming (CAD)The phenomenon in which a low-level cold air mass is trapped topographically. Often, this cold air is entrenched on the east side of mountainous terrain. Cold Air Damming often implies that the trapped cold air mass is influencing the dynamics of the overlying air mass, e.g. in an overrunning scenario.
Effects on the weather may include cold temperatures, freezing precipitation, and extensive cloud coverCounty Warning and Forecast AreaThe group of counties for which a National Weather Service Forecast Office is responsible for issuing warnings and weather forecasts.Critical DepthIn hydrologic terms, The depth of water flowing in an open channel or conduit, partially filled, corresponding to one of the recognized critical velocities.Critical FlowIn hydrologic terms, a condition of flow where the mean velocity is at one of the critical values; ordinarily at Belanger's critical depth and velocity. Another important usage is in reference to the Reynolds' critical velocities which define the point at which the flow changes from streamline or nonturbulent to turbulent flow. Critical Rainfall Probability(Abbrev. CRP) - In hydrologic terms, the Probability that the actual precipitation during a rainfall event has exceeded or will exceed the flash flood guidance value. Daily Climatological ReportAs the name indicates, this climatological product is issued daily by each National Weather Service office. Most of the climatological data in this report are
presented in a tabular form; however, some narrative statements may also be used in the product. The report is organized so that similar items are grouped together (i.e., temperature,
precipitation, wind, sunrise and sunset times, etc.).DecadalOccurring over a 10-year period, such as an oscillation whose period is roughly 10 years ("Pacific Decadal Oscillation").DesertificationA tendency toward more prominent desert conditions in a region.Ensemble ForecastMultiple predictions from an ensemble of slightly different initial conditions and/or various versions of models. The objectives are to improve the accuracy of the forecast through averaging the various forecasts, which eliminates non-predictable components, and to provide reliable information on forecast uncertainties from the diversity amongst ensemble members. Forecasters use this tool to measure the likelihood of a forecast.Ensemble Hydrologic ForecastingIn hydrologic terms, a process whereby a continuous hydrologic model is successively executed several times for the same forecast period by use of
varied data input scenarios, or a perturbation of a key variable state for each model run. A common method employed to obtain a
varied data input scenario is to use the historical meteorological record, with the assumption that several years of observed data
covering the time period beginning on the current date and extending through the forecast period comprises a reasonable estimate
of the possible range of future conditions.Environment CanadaThe Canadian federal government department responsible for issuing weather forecasts and weather warnings in Canada.Exclusive Flood Control Storage CapacityIn hydrologic terms, the space in a reservoir reserved for the sole purpose of regulating flood inflows to abate flood damageExtended Forecast DiscussionThis discussion is issued once a day around 2 PM EST (3 PM EDT) and is primarily intended to provide insight into guidance forecasts for the 3-
to 5-day forecast period. The geographic focus of this discussion is on the United States (including Alaska and Hawaii). Although portions of this narrative will parallel the
Hemispheric Map Discussion, a much greater effort is made to routinely relate the model forecasts and necessary modifications to weather forecasts, mainly in terms of temperature and
precipitation. ExtratropicalA term used in advisories and tropical summaries to indicate that a cyclone has lost its "tropical" characteristics. The term implies both poleward displacement of the
cyclone and the conversion of the cyclone's primary energy source from the release of latent heat of condensation to baroclinic (the temperature contrast between warm and cold air
masses) processes. It is important to note that cyclones can become extratropical and still retain winds of hurricane or tropical storm force.Extratropical CycloneA cyclone in the middle and high latitudes often being 2000 kilometers in diameter and usually containing a cold front that extends toward the equator for hundreds of kilometers.Extratropical LowA low pressure center which refers to a migratory frontal cyclone of middle and higher latitudes. Tropical cyclones occasionally evolve into extratropical lows losing tropical characteristics and become associated with frontal discontinuity. F ScaleAbbreviation for Fujita Scale, a system of rating the intensity of tornadoes; for detailed information, see the definition for that term.Field (Moisture) CapacityThe amount of water held in soil against the pull of gravityFlood CategoriesTerms defined for each forecast point which describe or categorize the severity of flood impacts in the corresponding river/stream reach. Each flood category is bounded by an upper and lower stage (see Example 1). The severity of flooding at a given stage is not necessarily the same at all locations along a river reach due to varying channel/bank characteristics or presence of levees on portions of the reach. Therefore, the upper and lower stages for a given flood category are usually associated with water levels corresponding to the most significant flood impacts somewhere in the reach. The flood categories used in the NWS are:
*Minor Flooding* - minimal or no property damage, but possibly some public threat.
*Moderate Flooding* - some inundation of structures and roads near stream. Some evacuations of people and/or transfer of property to higher elevations.
*Major Flooding* - extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.
*Record Flooding* - flooding which equals or exceeds the highest stage or discharge at a given site during the period of record keeping.
Note: all three of the lower flood categories (minor, moderate, major) do not necessarily exist for a given forecast point. For example, at the level where a river reaches flood stage, it may be considered moderate flooding. However, at least one of these three flood categories must start at flood stage. ForecastA statement of prediction.Forecast CrestIn hydrologic terms, the highest elevation of river level, or stage, expected during a specified storm event.Forecast GuidanceComputer-generated forecast materials used to assist the preparation of a forecast, such as numerical forecast models.Forecast Issuance StageThe stage which, when reached by a rising stream, represents the level where RFCs need to begin issuing forecasts for a non-routine (flood-only) forecast point. This stage is coordinated between WFO and RFC personnel and is not necessarily the same as action or alert stage. The needs of WFO/RFC partners and other users are considered in determining this stage. Forecast PeriodsOfficial definitions for NWS products:
Today...............................Sunrise to sunset
This afternoon..................noon till 6 p.m.
This evening.....................6 p.m. till sunset
Tonight.............................sunset till sunrise
Tomorrow.........................sunrise to sunset of the following dayForecast PointA location along a river or stream for which hydrologic forecast and warning services are provided by a WFO. The observed/forecast stage or discharge for a given forecast point can be assumed to represent conditions in a given reach (see /reach/).Forecast valid forThe period of time the forecast is in effect
beginning at a given day, date and time, and ending at a given day, date
and time.Fujita Scale(or F Scale) - A scale of tornado intensity in which wind speeds are inferred from an analysis of wind damage:
|F0 (weak)||40-72 mph, light damage
|F1 (weak)||73-112 mph, moderate damage
|F2 (strong)||113-157 mph, considerable damage
|F3 (strong)||158-206 mph, severe damage
|F4 (violent)||207-260 mph, devestating damage
|F5 (violent)||260-318 mph (rare), incredible damage
All tornadoes, and most other severe local windstorms, are assigned a single number from this scale according to the most intense damage caused by the storm.Full-Physics Numerical ModelA computer model used to calculate air pollution concentrations. A full-physics numerical model uses a full set of equations describing the thermodynamic and dynamic state of the atmosphere and can be used to simulate atmospheric phenomena.Geophysical EventsIn solar-terrestrial terms, flares (Importance two or larger) with Centimetric
Outbursts (maximum of the flux higher than the Quiet Sun flux,
duration longer 10 minutes) and/or strong SID. Sometimes these
flares are followed by Geomagnetic Storms or small PCA. (Class M
Flares)Global Ensemble Forecast System (GEFS)A weather forecast model made up of 21 separate forecasts, or ensemble members. The National Centers for Environmental Prediction (NCEP) started the GEFS to address the nature of uncertainty in weather observations, which are used to initialize weather forecast models.Global Forecast System(GFS)- One of the operational forecast models run at NCEP. The GFS is run four times daily, with forecast output out to 384 hours.Great Lakes Marine Forecast (MAFOR)A National Weather Service coded summary appended to each of the Great Lakes Open Lakes forecasts. Great Lakes Weather Broadcast(LAWEB) - A National Weather Service product containing an observation summary prepared to provide Great Lakes mariners with a listing of weather observations along or on the Lakes.HectopascalA unit of pressure equal to a millibar (1 hPa = 1 mb). Abbreviated hPa.High Resolution Ensemble Forecast (HREF)An ensemble of products from several different models running at ~3 km horizontal grid spacing.High Seas Forecast(HSF) - Marine forecasts for the major oceans of the world. In this context, major gulfs or seas (e.g., the Gulf of Mexico or the Bering Sea) are included within these forecast areas. Areas of responsibility for the U.S. are determined by international agreements under the auspices of the World Meteorological Organization (WMO).Hurricane(abbrev. HURCN) A tropical cyclone in the Atlantic, Caribbean Sea, Gulf of Mexico, or eastern Pacific, which the maximum 1-minute sustained surface wind is 64 knots (74 mph) or greater.Hurricane Force Wind WarningA warning for sustained winds, or frequent gusts, of 64 knots (74 mph) or greater, either predicted or occurring, and not directly associated with a tropical
cyclone. Hurricane Force Wind WatchA watch for an increased risk of a hurricane force wind event for sustained surface winds, or frequent gusts, of 34 knots 64 knots (74 mph) or greater, but its occurrence, location, and/or timing is still uncertain.Hurricane Local StatementA public release prepared by local National Weather Service offices in or near a
threatened area giving specific details for its county/parish warning area on
(2) evacuation decisions made by local officials
precautions necessary to protect life and property.Hurricane SeasonThe part of the year having a relatively high incidence of tropical cyclones. In the Atlantic, Caribbean, and Gulf of Mexico, and central North Pacific, the hurricane season is the period from June through November; in the eastern Pacific, May 15 through November 30. Tropical cyclones can occur year-round in any basin.Hurricane WarningAn announcement that hurricane conditions (sustained winds of 74 mph or higher) are expected somewhere within the specified coastal area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds. The warning can remain in effect when dangerously high water or a combination of dangerously high water and waves continue, even though winds may be less than hurricane force. Hurricane WatchAn announcement that hurricane conditions (sustained winds of 74 mph or higher) are possible within the specified coastal area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical-storm-force winds.Hydrologic Ensemble Forecast System (HEFS)A probabilistic forecast tool with the goals to provide hydrologic forecasts including an analysis of “probable outcomes” and to minimize biases in the atmospheric models and in the hydrologic models.Inactive Storage CapacityIn hydrologic terms, the portion of capacity below which the reservoir is not normally drawn, and which is provided for
sedimentation, recreation, fish and wildlife, aesthetic reasons, or for the creation of a minimum controlled operational or power head in
compliance with operating agreements or restrictions.Infiltration CapacityIn hydrologic terms, the maximum rate at which water can enter the soil at a particular point under a given set of conditions.Intertropical Convergence Zone(ITCZ) The region where the northeasterly and southeasterly trade winds converge, forming an often continuous band of clouds or thunderstorms near the equator. Kelvin Temperature ScaleAn absolute temperature scale in which a change of 1 Kelvin equals a change of 1 degree Celsius; 0ºK is the lowest temperature on the Kelvin scale. The freezing point of water is +273ºK (Kelvin) and the boiling point of +373ºK. It is used primarily for scientific purposes. It is also known as the Absolute Temperature Scale.KilopascalThe internationally recognized unit used by the Atmospheric Environment Service for measuring atmospheric pressure. Abbreviated kPa.Large Scale(Synoptic Scale) Size scale referring generally to weather systems with horizontal dimensions of several hundred miles or more. Most high and low
pressure areas seen on weather maps are synoptic-scale systems.LCD (Local Climatological Data)This National Climatic Data Center (NCDC) publication is produced monthly and annually for some 270 United States cities and it's territories. The
LCD summarizes temperature, relative humidity, precipitation, cloudiness, wind speed and direction observation. Live CapacityIn hydrologic terms, the total amount of storage capacity available in a reservoir for all purposes, from the dead storage level to the normal water or
normal pool level surface level. Does not include surcharge, or dead storage, but does include inactive storage, active conservation
storage and exclusive flood control storage.Local Convective WindIn fire weather terminology, local thermally driven winds arising over a comparatively small area and influenced by local terrain. Examples include sea and land breezes, lake breezes, diurnal mountain wind systems and columnar convective currents.MacroscaleLarge scale, characteristic of weather systems several hundred to several thousand kilometers in diameter.Major HurricaneA hurricane which reaches Category 3 (sustained winds greater than 110 mph) on the Saffir/Simpson Hurricane Scale. Maritime Tropical Air MassAn air mass characterized by warm, moist air. Abbreviated mT.Medium Range Forecast (MRF)A configuration of the National Water Model (NWM) that runs every 6 hours and produces 3-hourly deterministic forecasts of streamflow and hydrologic states for the contiguous United States (ConUS). This configuration is an ensemble forecast with 7 members; member 1 extends out to 10 days, while members 2-7 extend out to 8.5 days. Meteorological forcing data are drawn from the GFS.MesoscaleSize scale referring to weather systems smaller than synoptic-scale systems but larger than
storm-scale systems. Horizontal dimensions generally range from around 50 miles to several hundred miles.
Squall lines, MCCs, and MCSs are examples of mesoscale weather systemsMesoscale Convective Complex(abbrev. MCC)- MCC - Mesoscale Convective Complex. A large Mesoscale Convective System (MCS), generally round or oval-shaped, which normally reaches peak intensity at night. The formal definition includes specific minimum criteria for size, duration, and eccentricity (i.e., "roundness"), based on the cloud shield as seen on infrared satellite photographs:
* Size: Area of cloud top -32 degrees C or less: 100,000 square kilometers or more (slightly smaller than the state of Ohio), and area of cloud top -52 degrees C or less: 50,000 square kilometers or more.
* Duration: Size criteria must be met for at least 6 hours.
* Eccentricity: Minor/major axis at least 0.7.
MCCs typically form during the afternoon and evening in the form of several isolated thunderstorms, during which time the potential for severe weather is greatest. During peak intensity, the primary threat shifts toward heavy rain and flooding.Mesoscale Convective System(MCS): A complex of thunderstorms which becomes organized on
a scale larger than the individual thunderstorms, and normally persists for several hours or more.
MCSs may be round or linear in shape, and include systems such as tropical cyclones, squall
lines, and MCCs (among others). MCS often is used to describe a cluster of thunderstorms that
does not satisfy the size, shape, or duration criteria of an MCC. Mesoscale DiscussionWhen conditions actually begin to shape up for severe weather, SPC (Storm Prediction Center) often issues a Mesoscale Discussion (MCD) statement anywhere from roughly half an hour to several hours before issuing a weather watch. SPC also puts out MCDs for hazardous winter weather events on the mesoscale, such as locally heavy snow, blizzards and freezing rain (see below). MCDs are also issued on occasion for heavy rainfall, convective trends, and other phenomena, when the forecaster feels he/she can provide useful information that is not readily available or apparent to field forecasters. MCDs are based on mesoscale analysis and interpretation of observations and of short term, high resolution numerical model output.
The MCD basically describes what is currently happening, what is expected in the next few hours, the meteorological reasoning for the forecast, and when/where SPC plans to issue the watch (if dealing with severe thunderstorm potential). Severe thunderstorm MCDs can help you get a little extra lead time on the weather and allow you to begin gearing up operations before a watch is issued. The MCD begins with a numerical string that gives the LAT/LON coordinates of a polygon that loosely describes the area being discussed.Mesoscale High WindsThese high winds usually follow the passage of organized convective systems and are associated with wake depressions or strong mesohighs.Meteorological Model Ensemble River Forecast (MMEFS)An automated short-term hydrologic ensemble forecast system which utilizes temperature and precipitation output from the National Centers for Environmental Prediction (NCEP) GEFS and NAEFS meteorological models as inputs to River Forecast Center hydrologic models.MicroscalePertaining to meteorological phenomena, such as wind circulations or cloud patterns, that are less than 2 km in horizontal extent.Mie ScatteringAny scattering produced by spherical particles whose diameters are greater than
1/10 the wavelength of the scattered radiation. This type of scattering causes the clouds to
appear white in the sky. Often, hail exhibits in this type of scattering.MisoscaleThe scale of meteorological phenomena that ranges in size from 40 meters to about 4 kilometers. It includes rotation within a thunderstorm.MLCAPEMean Layer CAPE - CAPE calculated using a parcel consisting of Mean Layer values of temperature and moisture from the lowest 100 mb above ground level. See Convective Available Potential Energy (CAPE).Monthly Climatological ReportThis climatological product is issued once a month by each
National Weather Service office. It is a mix of tabular and narrative information. It is organized so
that similar items are grouped together (i.e., temperature, precipitation, wind, heating/cooling
degree information, etc.). Mount Wilson Magnetic ClassificationsIn solar-terrestrial terms, a classification system for sunspots:
National Digital Forecast Database(NDFD)- The National Weather Service's NDFD provides access to gridded forecasts of sensible weather elements (e.g., wind, wave height) through the National Digital Forecast Database (NDFD). NDFD contains a seamless mosaic of digital forecasts from NWS field offices working in collaboration with the National Centers for Environmental Prediction (NCEP). The database is made available to all customers and partners from the public, private and academic sectors. Those customers and partners may use this data to create a wide range of text, graphic, gridded and image products of their own. National Hurricane Center One of three branches of the Tropical Prediction Center (TPC). This center maintains a continuous watch on tropical cyclones over the Atlantic, Caribbean, Gulf of Mexico, and the Eastern Pacific from 15 May through November 30. The Center prepares and distributes hurricane watches and warnings for the general public, and also prepares and distributes marine and military advisories for other users. During the "off-season" NHC provides training for U.S. emergency managers and representatives from many other countries that are affected by tropical cyclones. NHC also conducts applied research to evaluate and improve hurricane forecasting techniques, and is involved in public awareness programs.National Hurricane Operations Plan(NHOP) - The NHOP is issued annually by the Federal Coordinator for Meteorological Services and Supporting Research. It documents interdepartmental agreements relating to tropical cyclone observing, warning, and forecasting services. National Hurricane Center (NHC), Central Pacific Hurricane Center (CPHC), and the JTWC serve as the principal offices in coordinating the day-to-day activities of the NWS in support of the Plan in their region of responsibility. National Water Model Medium-Range Forecast (NWM MRF)A 10-day streamflow forecast for the over 3.6 million waterway miles across the Nation, forced by the GFS and updated every 6 hours.National Water Model Short-Range Forecast (NWM SRF)An 18-hour streamflow forecast for the over 3.4 million waterway miles across the Nation, forced by the HRRR and updated hourly.Nautical DawnThe time at which the sun is 12 degrees below the horizon in the morning. Nautical dawn is defined as that time at which there is just enough sunlight for objects to be distiguishable. Nautical DuskThe time at which the sun is 12 degrees below the horizon in the evening. At this time, objects are no longer distinguishable. Nautical MileA unit of distance used in marine navigation and marine forecasts. It is equal to 1.15 statue miles or 1852 meters. It is also the length of 1 minute of latitude.Nautical TwilightThe time after civil twilight, when the brighter stars used for celestial navigation have appeared and the horizon may still be seen. It ends when the center of the sun is 12 degrees below the horizon, and it is too difficult to perceive the horizon, preventing accurate sighting of stars.NAVTEX Forecast(NAV) - A National Weather Service marine forecast combining various Coastal Waters and Offshore forecasts, optimized to accommodate transmission via NAVTEX. NCARNational Center for Atmospheric ResearchNearshore Forecast(NSH) - National Weather Service seasonal marine forecasts for an areas of the Great Lakes extending from a line approximating mean low water datum along the coast or an island, including bays, harbors, and sounds, out to 5 nm. These forecasts are normally issued from Daylight Savings Time ~April 7 through December 31, though the dates may be shortened or extended based on local/regional requirements. North American Ensemble Forecast System (NAEFS)An atmospheric ensemble of 20 members each from the NCEP GEFS and CMC EPS ensemble systems.North American Mesoscale Forecast System (NAM)One of the major weather models run by the National Centers for Environmental Prediction (NCEP) for producing weather forecasts.NowcastA short-term weather forecast, generally out to six hours or less. This is also called a Short Term Forecast.Numerical ForecastingA computer forecast or prediction based on equations governing the motions and the forces affecting motion of fluids. The equations are based, or initialized, on specified weather or climate conditions at a certain place and time.Numerical Weather PredictionSame as Numerical Forecasting; a computer forecast or prediction based on equations governing the motions and the forces affecting motion of fluids. The equations are based, or initialized, on specified weather or climate conditions at a certain place and time. Offshore Waters Forecast(OFF) - A National Weather Service marine forecast product for that portion of the oceans, gulfs, and seas beyond the coastal waters extending to a specified distance from the coastline, to a specified depth contour, or covering an area defined by specific latitude and longitude points. Open Lakes Forecast(GLF) - A National Weather Service marine forecast product for the U.S. waters within a Great Lake not including the waters covered by an existing Nearshore Waters Forecast (NSH). When the seasonal Nearshore forecast is not issued, the Open Lake forecast includes a forecast of nearshore waters. Overcast(Abbrev. OVC)- An official sky cover classification for aviation weather observations, when the sky is completely covered by an obscuring phenomenon. This is applied only when obscuring phenomenon aloft are present--that is, not when obscuring phenomenon are surface-based, such as fog.Pacific Decadal Oscillation(Abbrev. PDO) - a recently described pattern of climate variation similar to ENSO though on a timescale of decades and not seasons. It is characterized by SST anomalies of one sign in the north-central Pacific and SST anomalies of another sign to the north and east near the Aleutians and the Gulf of Alaska. It primarily affects weather patterns and sea surface temperatures in the Pacific Northwest, Alaska, and northern Pacific Islands.Pancake IceIn hydrologic terms, circular flat pieces of ice with a raised rim; the shape and rim are due to repeated collisionsPascalThe unit of pressure produced when one newton acts on one square meter (1 N/m2). It is abbreviated Pa.Persistence ForecastA forecast that the current weather condition will persist and that future weather will be the same as the present (e.g., if it is raining today, a forecast predicting rain tonight).Phenomenological ModelA computer model used to calculate air pollution concentrations. A phenomenological model focuses on an individual phenomenon, such as plume impingement or fumigation.Photochemical SmogAir pollution containing ozone and other reactive chemical compounds formed by the reaction of nitrogen oxides and hydrocarbons in the presence of sunlight.Plan Position IndicatorAn acronym for Plan Position Indicator. A PPI displays radar data horizontally using a map projection. In PPI mode, the radar makes a 360-degree sweep with the antenna at a specific elevation angle. A PPI display is the familiar radar display shown on the television weather programs.Polar Cap Absorption (PCA)In solar-terrestrial terms, an anomalous condition of the polar ionosphere whereby HF and VHF (3 - 300 MHz) radiowaves are absorbed, and LF and VLF (3 - 300 kHz) radiowaves are reflected at lower altitudes than normal. In practice, the absorption is inferred from the proton flux at energies greater than 10 MeV, so that PCAs and
proton events are simultaneous. Transpolar radio paths may still be disturbed for days, up to weeks, following the end of a proton event.Pre-Hurricane Squall LineIt is often the first serious indication that a hurricane is approaching. It is a generally a straight line and resembles a squall-line that occurs with a mid-latitude cold front. It is as much as 50 miles or even more before the first ragged rain echoes of the hurricane's bands and is usually about 100 to 200 miles ahead of the eye, but it has been observed to be as much as 500 miles ahead of the eye in the largest hurricanes.Prevention of Significant DeteriorationA program, specified in the Clean Air Act, whose goal is to prevent air quality from deteriorating significantly in areas of the country that are presently meeting the ambient air quality standards.Probability ForecastA forecast of the probability that one or more of a mutually exclusive set of weather conditions will occur.Probability of Tropical Cyclone ConditioThe probability, in percent, that the cyclone center will pass within 50 miles to the
right or 75 miles to the left of the listed location within the indicated time period
when looking at the coast in the direction of the cyclone's movement.Quantitative Precipitation ForecastA spatial and temporal precipitation forecast that will predict the potential amount of future precipitation for a specified region, or area.Range Height IndicatorThe RHI is a radar display in which the radar scans vertically, with the antenna pointing at a specific azimuth or radial. NEXRAD does not support RHI, but the PUP software allows the NEXRAD operator to construct a vertical cross-section using data from multiple scans of the radar.Rayleigh ScatteringChanges in directions of electromagnetic energy by particles whose diameters are 1/16 wavelength or less. This type of scattering is responsible for the sky being blue.RelocatedA term used in an advisory to indicate that a vector drawn from the preceding advisory position to the latest known position is not necessarily a reasonable representation of the cyclone's movement.River ForecastAn internal product issued by RFCs to other NWS offices. An RVF contains stage and/ or flow forecasts for specific locations based on existing, and forecasted hydrometeorologic conditions. The contents of these products are used by the HSA office to prepare Flood Warnings (FLW), Flood Statements (FLS), River Statements (RVS), as well as other products available to the public.River Forecast CenterCenters that serve groups of Weather Service Forecast offices and Weather Forecast offices, in providing hydrologic guidance and is the first echelon office for the preparation of river and flood forecasts and warnings.Saffir-Simpson Hurricane Wind ScaleThe Saffir-Simpson Hurricane Wind Scale is a 1 to 5 categorization based on the hurricane's intensity at the indicated time. The scale provides examples of the type of damage and impacts in the United States associated with winds of the indicated intensity. In general, damage rises by about a factor of four for every category increase. The maximum sustained surface wind speed (peak 1-minute wind at the standard meteorological observation height of 10 m [33 ft] over unobstructed exposure) associated with the cyclone is the determining factor in the scale. The scale does not address the potential for other hurricane-related impacts, such as storm surge, rainfall-induced floods, and tornadoes.
SBCAPESurface Based CAPE; CAPE calculated using a Surface based parcel.SCASmall Craft AdvisoryScatteredWhen used to describe precipitation (for example: "scattered showers") - Area coverage of convective weather affecting 30 percent to 50 percent of a forecast zone (s).
When used to describe sky cover: 3/8th to 4/8th (sky cover is measured in eighths or oktas) of the sky covered by clouds. In U.S. weather observing procedures, this is reported with the contraction “SCT.”ScatteringThe process in which a beam of light is diffused or deflected by collisions with particles suspended in the atmosphere.Sectorized Hybrid ScanA single reflectivity scan composed of data from the lowest four elevation scans. Close to the radar, higher tilts are used to reduce clutter. At further ranges, either the maximum values from the lowest two scans are used or the second scan values are used alone.Sediment Storage CapacityIn hydrologic terms, the volume of a reservoir planned for the deposition of sediment.Severe Local StormA convective storm that usually covers a relatively small geographic area, or moves in a narrow path, and is sufficiently intense to threaten life and/or property. Examples include severe thunderstorms with large hail, damaging wind, or tornadoes. Although cloud-to-ground lightning is not a criteria for severe local storms, it is acknowledged to be highly dangerous and a leading cause of deaths, injuries, and damage from thunderstorms. A thunderstorm need not be severe to generate frequent cloud-to-ground lightning. Additionally, excessive localized convective rains are not classified as severe storms but often are the product of severe local storms. Such rainfall may result in related phenomena (flash floods) that threaten life and property.Severe Local Storm WatchAn alert issued by the National Weather Service for the contiguous U.S. and its adjacent waters of the potential for severe thunderstorms or tornadoes. Short Range Forecast (SRF)A configuration of the National Water Model (NWM) that runs hourly and produces hourly deterministic forecasts of streamflow and hydrologic states out to 18 hours for the contiguous United States (ConUS), and out 48 hours for Hawaii and Puerto Rico/U.S. Virgin Islands. For ConUS, meteorological forcing data are drawn from the HRRR and RAP. For Hawaii and Puerto Rico/U.S. Virgin Islands, meteorological forcing data are drawn from the NAM-Nest with HIRESW WRF-ARW.Short Term ForecastA product used to convey information regarding weather or hydrologic events in the next few hours.Significant Wave HeightThe mean or average height of the highest one third of all waves in a swell train or in a wave generating region. It approximates the value an experienced observer would report if visually estimating sea height. When expressed as a range (e.g. Seas 2-4 ft) , indicates a degree of uncertainty in the forecast and/or expected changing conditions (not that all waves are between 2-4 ft). Generally, it is assumed that individual wave heights can be described using a Rayleigh distribution.
- Alpha: Denotes a unipolar sunspot group.
- Beta: A sunspot group having both positive and negative magnetic polarities, with a simple and distinct division between the polarities.
- Beta-Gamma: A sunspot group that is bipolar but in which no continuous line can be drawn separating spots of opposite polarities.
- Delta: A complex magnetic configuration of a solar sunspot group consisting of opposite polarity umbrae within the same penumbra.
- Gamma: A complex active region in which the positive and negative polarities are so irregularly distributed as to prevent classification as a bipolar group.
Example: Significant Wave Height = 10 ft
1 in 10 waves will be larger than 11 ft
1 in 100 waves will be larger than 16 ft
1 in 1000 waves will larger than 19 ft
Therefore, assuming a wave period of 8 seconds, for a significant wave height of 10 feet, a wave 19 feet or higher will occur every 8,000 seconds (2.2 hours).
Significant Weather OutlookA narrative statement produced by the National Weather Service, frequently issued on a routine basis, to
provide information regarding the potential of significant weather expected during the next 1 to 5 days.Small Craft Should Exercise CautionPrecautionary statement issued to alert mariners with small, weather sensitive boats. Special Tropical Disturbance StatementThis statement issued by the National Hurricane Center furnishes information on strong and formative non-depression systems. 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).Sphere CalibrationReflectivity calibration of a radar by pointing the dish at a metal sphere of (theoretically) known reflectivity. The sphere is often tethered to a balloon.Staccato LightningA Cloud to Ground (CG) lightning discharge which appears as a single very bright, short-duration stroke, often with considerable branching.State Forecast ProductThis National Weather Service product is intended to give a good general picture of what weather may be expected in the state during the next 5 days. The first 2 days of the forecast is much more specific than the last 3 days. In comparison with the Zone Forecast Product, this product will be much more general.Storm ScaleReferring to weather systems with sizes on the order of individual thunderstorms. See synoptic scale and mesoscale.Subtropical CycloneA non-frontal low pressure system that has characteristics of both tropical and extratropical cyclones. This system is typically an upper-level cold low with circulation extending to the surface layer and maximum sustained winds generally occurring at a radius of about 100 miles or more from the center. In comparison to tropical cyclones, such systems have a relatively broad zone of maximum winds that is located farther from the center, and typically have a less symmetric wind field and distribution of convection.Subtropical DepressionA subtropical cyclone in which the maximum 1-minute sustained surface wind is 33 knots (38 mph) or less. Subtropical Jet(Abbrev. STJ) - this jet stream is usually found between 20° and 30° latitude at altitudes between 12 and 14 km.Subtropical StormA subtropical cyclone in which the maximum 1-minute sustained surface wind is 34 knots (39 mph) or more. Sunspot Group Classification
Surcharge CapacityIn hydrologic terms, 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.Surf Zone Forecast(SRF) - A National Weather Service routine or event driven forecast product geared toward non-boating marine users issued for an area extending from the area of water between the high tide level on the beach and the seaward side of the breaking waves. Synoptic ScaleThe spatial scale of the migratory high and low pressure systems of the lower troposphere, with wavelengths of 1000 to 2500 km.Terminal Aerodrome ForecastThis NWS aviation product is a concise statement of the expected meteorological conditions at an airport during a specified period (usually 24 hours). Each country is allowed to make modifications or exceptions to the code for use in each particular country. TAFs use the same weather code found in METAR weather reports.Tropical AdvisoryOfficial information issued by tropical cyclone warning centers describing all tropical
cyclone watches and warnings in effect along with details concerning tropical
cyclone locations, intensity and movement, and precautions that should be taken.
Advisories are also issued to describe: (a) tropical cyclones prior to issuance of
watches and warnings and (b) subtropical cyclones.Tropical Analysis and Forecast BranchOne of three branches of the Tropical Prediction Center (TPC). It provides year-round products involving marine forecasting, aviation forecasts and warnings (SIGMETs), and surface analyses. The unit also provides satellite interpretation and satellite rainfall estimates for the international community. In addition, TAFB provides support to NHC through manpower and tropical cyclone intensity estimates from the Dvorak technique.Tropical CycloneA warm-core, non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters with organized deep convection and a closed surface wind circulation about a well-defined center.Tropical Cyclone Plan of the DayA coordinated mission plan that tasks operational weather reconnaissance requirements during the next 1100 to 1100 UTC day or as required, describes reconnaissance flights committed to satisfy both operational and research requirements, and identifies possible reconnaissance requirements for the succeeding 24-hour period.Tropical Cyclone Position EstimateThe National Hurricane Center issues a position estimate between scheduled advisories whenever the storm center is within 200 nautical miles of U.S. land-based weather radar and if sufficient and regular radar reports are available to the hurricane center. As far as is possible, the position estimate is issued hourly near the beginning of the hour. The location of the eye or storm center is given in map coordinates and distance and direction from a well-known point. Tropical Cyclone UpdateThis brief statement is issued by the National Hurricane Center in lieu of or preceding special advisories to inform of significant changes in a tropical cyclone or the posting or cancellation of watches and warnings.Tropical DepressionA tropical cyclone in which the maximum 1-minute sustained surface wind is 33 knots (38 mph) or less.Tropical DisturbanceA discrete tropical weather system of apparently organized convection--generally 100 to 300 mi in diameter--originating in the tropics or subtropics, having a nonfrontal migratory character and maintaining its identity for 24 hours or more. It may or may not be associated with a detectable perturbation of the wind field.Tropical StormA tropical cyclone in which the maximum 1-minute sustained surface wind ranges from 34 to 63 knots (39 to 73 mph) inclusive.Tropical Storm SummaryWritten by the Hydrometeorological Prediction Center* (HPC) after subtropical and names tropical cyclones have moved inland and advisories have been discontinued. These advisories will be terminated when the threat of flash flooding has ended or when the remnants of these storms can no longer be distinguished from other synoptic features capable of producing flash floods. Storm summaries will not be issued for storms that enter the coast of Mexico and do not pose an immediate flash flood threat to the coterminous United States. They will be initiated when and if flash flood watches are posted in the United States because of an approaching system. Storm summaries will continue to be numbered in sequence with tropical cyclone advisories and will reference the former storm's name in the text. Summaries will be issued at 0100, 0700, 1300, and 1900 Eastern Daylight Time (EDT). The only exception will be the first one in the series may be issued at a nonscheduled time.Tropical Storm WarningAn announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are expected somewhere within the specified coastal area within 36 hours.Tropical Storm WatchAn announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are possible within the specified coastal area within 48 hours.Tropical Wave(formerly known as inverted trough) - A trough or cyclonic curvature maximum in the trade wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere or may be the reflection of an upper tropospheric cold low or an equatorward extension of a mid-latitude trough.Tropical Weather DiscussionThese messages are issued 4 times daily by the Tropical Analysis and Forecast Branch (TAFB) to describe significant synoptic weather features in the tropics. One message will cover the Gulf of Mexico, the Caribbean, and the Atlantic between the equator and 32 degrees North and east of 140 degrees West. Plain language is used in these discussions.Tropical Weather OutlookThis outlook normally covers the tropical and subtropical waters, discussing the weather conditions, emphasizing any disturbed and suspicious areas which may become favorable for tropical cyclone development within the next day to two. In the Atlantic, the outlook is transmitted daily at 0530, 1130, 1730, and 2230 Eastern local time. In the eastern Pacific, it is transmitted daily at 0100, 0700, 1300, and 1900 Eastern local time. For the Central Pacific, transmission times are 1000 and 2200 UTC. Existing tropical and subtropical cyclones are mentioned, as are depressions not threatening land. Given for each system are its location, size, intensity, and movement. For the first 24 hours of a depression or tropical cyclone, the outlook includes a statement identifying the AFOS and World Meteorological Organization (WMO) headers for the advisory on it.Tropical Weather SummaryThe National Hurricane Center issues a monthly summary of tropical weather is included at the end of the month or as soon as feasible thereafter, to describe briefly the past activity or lack thereof and the reasons why.U.S. Geological Survey(Abbrev. USGS)- The Federal Agency chartered in 1879 by congress to classify public lands, and to examine the geologic structure, mineral
resources, and products of the national domain. As part of its mission, the USGS provides information and data on the Nation’s
rivers and streams that are useful for mitigation of hazards associated with floods and droughts.Variable Infiltration Capacity (VIC)A large-scale, semi-distributed hydrologic model that solves full water and energy balances. As such, it shares several basic features with other land surface models that are commonly coupled to global circulation models.Vertical VelocityThe component of velocity (motion) in the vertical. The evaluation of areas of upward vertical velocity is key to forecasting areas of active
weather.Vertical Wind Shearthe change in the wind's direction and speed with height. This is a critical factor in determining whether severe thunderstorms will develop.Vertically Stacked SystemA low-pressure system, usually a closed low or cutoff low, which is not tilted with height, i.e., located similarly at all levels of the atmosphere. Such systems typically are weakening and are slow-moving, and are less likely to produce severe weather than tilted systems. However, cold pools aloft associated with vertically-stacked systems may enhance instability enough to produce severe weather.
Volcanic AshFine particles of mineral matter from a volcanic eruption which can be dispersed long distances by winds aloft. The chemical composition and abrasiveness of the particles can seriously affect aircraft and also machinery on the ground. If it is blown into the stratosphere and it is thick enough, it can decrease the global temperature.Volume ScanA radar scanning strategy in which sweeps are made at successive antenna elevations (i.e., a tilt sequence), and then combined to obtain the three-dimensional structure of the echoes.Watch CancellationThis product will be issued to let the public know when either a Tornado Watch or Severe Thunderstorm Watch has been canceled early. It is issued by the Storm Prediction Center (SPC) in Norman, Oklahoma. In the text of the statement it will specify the severe weather watch number and the area which the watch covered.Weather Forecast Office(Abbrev. WFO) - this type of National Weather Service office is responsible for issuing advisories, warnings, statements, and short term forecasts for its county warning areaWest African Disturbance LineA line of convection about 300 miles long, similar to a squall line. It forms over west Africa north of the equator and south of 15 degrees North latitude. It moves faster than an Easterly Wave between 20 and 40 mph. They move off the African coast every 4 to 5 days mainly in the summer. Some reach the American tropics and a few develop into tropical cyclones.WhitecapThe breaking crest of a wave, usually white and frothy.Zurich Sunspot ClassificationIn solar-terrestrial terms, a sunspot classification system that has been
modified for SESC use.
- A: A small single unipolar sunspot or very small group of spots without penumbra.
- B: Bipolar sunspot group with no penumbra.
- C: An elongated bipolar sunspot group. One sunspot must have penumbra.
- D: An elongated bipolar sunspot group with penumbra on both ends of the group.
- E: An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 10 deg. but not 15 deg.
- F: An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 15 deg.
- H: A unipolar sunspot group with penumbra.
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