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Active Conservation StorageIn hydrologic terms, the portion of water stored in a reservoir that can be released for all useful purposes such as municipal water supply, power, irrigation, recreation, fish, wildlife, etc. Conservation storage is the volume of water stored between the inactive pool elevation and flood control stage. 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. Air Mass ThunderstormGenerally, a thunderstorm not associated with a front or other type of synoptic-scale forcing mechanism. Air mass thunderstorms typically are associated with warm, humid air in the summer months; they develop during the afternoon in response to insolation, and dissipate rather quickly after sunset. They generally are less likely to be severe than other types of thunderstorms, but they still are capable of producing downbursts, brief heavy rain, and (in extreme cases) hail over 3/4 inch in diameter.
Since all thunderstorms are associated with some type of forcing mechanism, synoptic-scale or otherwise, the existence of true air-mass thunderstorms is debatable.Back-building ThunderstormA thunderstorm in which new development takes place on the upwind side (usually the west or southwest side), such that the storm seems to remain stationary or propagate in a backward direction.Bank StorageIn hydrologic terms, water absorbed and stored in the void in the soil cover in the bed and banks of a stream, lake, or reservoir, and returned in whole or in part as the level of water body surface falls.Complex Gale/Storm In the high seas and offshore forecasts, an area for which gale/storm force winds are forecast or are occurring but for which no single center is the principal generator of these winds.Conservation StorageIn hydrologic terms, storage of water for later release for usual purposes such as municipal water supply, power, or irrigation in contrast with storage capacity used for flood control.Continuum Storm (CTM)In solar-terrestrial terms, general term for solar noise lasting for hours and
sometimes days.Cyclic StormA thunderstorm that undergoes cycles of intensification and weakening (pulses)
while maintaining its individuality. Cyclic supercells are capable of producing multiple tornadoes (i.e.,
a tornado family) and/or several bursts of severe weather.Dead StorageIn hydrologic terms, the volume in a reservoir below the lowest controllable level.Depression StorageIn hydrologic terms, the volume of water contained in natural depressions in the land surface, such as puddles.Detention StorageIn hydrologic terms, the volume of water, other than depression storage, existing on the land surface as flowing water which has not yet reached the
channel.Developing Gale/StormIn the high seas and offshore forecasts, a headline used in the warnings section to indicate that gale/storm force winds are not now occurring but are expected before the end of the forecast period. Dry Line StormAny thunderstorm that develops on or near a dry line.Dry ThunderstormGenerally a high-based thunderstorm when lightning is observed, but little if any precipitation reaches the ground. Most of the rain produced by the thunderstorm evaporates into relatively dry air beneath the storm cell. May also be referred to as "dry lightning". Dust StormA severe weather condition characterized by strong winds and dust-filled air over an extensive area.Energy DissipatorIn hydrologic terms, a structure which slows fast-moving spillway flows in order to prevent erosion of the stream channel.Exclusive Flood Control Storage CapacityIn hydrologic terms, the space in a reservoir reserved for the sole purpose of regulating flood inflows to abate flood damageFlood Control StorageIn hydrologic terms, storage of water in reservoirs to abate flood damageGeomagnetic StormIn solar-terrestraial terms, a worldwide disturbance of the earth's magnetic field,
distinct from regular diurnal variations.
Minor Geomagnetic Storm: A storm for which the Ap index was
greater than 29 and less than 50.
Major Geomagnetic Storm: A storm for which the Ap index was
greater than 49 and less than 100.
Severe Geomagnetic Storm: A storm for which the Ap index was
100 or more.
Initial Phase: Of a geomagnetic storm, that period when there
may be an increase of the middle-latitude horizontal
intensity (H).
Main Phase: Of a geomagnetic storm, that period when the hori-
zontal magnetic field at middle latitudes is generally
decreasing.
Recovery Phase: Of a geomagnetic storm, that period when the
depressed northward field component returns to normal levels.Great Lakes Storm Summary(GLS) - A National Weather Service forecast product providing updated information whenever a storm warning is in effect on any of the Great Lakes.High Risk (of severe thunderstorms)Severe weather is expected to affect more than 10 percent of the
area. A high risk is rare, and implies an unusually dangerous situation and usually the possibility of a major
severe weather outbreak.HP Stormor HP Supercell - High-Precipitation storm (or High-Precipitation supercell). A supercell thunderstorm in which heavy precipitation (often including hail) falls on the trailing side of the mesocyclone.
Precipitation often totally envelops the region of rotation, making visual identification of any embedded tornadoes difficult and very dangerous. Unlike most classic supercells, the region of rotation in many HP storms develops in the front-flank region of the storm (i.e., usually in the eastern portion). HP storms often produce extreme and prolonged downburst events, serious flash flooding, and very large damaging hail events.Ice StormAn ice storm is used to describe occasions when damaging accumulations of ice are expected during freezing rain situations. Significant accumulations of ice pull down trees and utility lines resulting in loss of power and communication. These accumulations of ice make walking and driving extremely dangerous. Significant ice accumulations are usually accumulations of ¼" or greater.Ice Storm WarningThis product is issued by the National Weather Service when freezing rain produces a significant and possibly damaging accumulation of ice. The criteria for this
warning varies from state to state, but typically will be issued any time more than 1/4" of ice is expected to accumulate in an area.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.Interception Storage RequirementsIn hydrologic terms, water caught by plants at the onset of a rainstorm. This must be met before rainfall reaches the ground.Ionospheric StormA disturbance in the F region of the ionosphere, which
occurs in connection with geomagnetic activityLake Effect StormA fall or winter storm that produces heavy but localized precipitation as a result of temperature differences between the air over snow-covered ground and the air over the open waters of a lake.Littoral ZoneIn hydrologic terms, the area on, or near the shore of a body waterLP StormLow-Precipitation storm (or Low-Precipitation supercell). A
supercell thunderstorm characterized by a relative lack of visible precipitation. Visually similar to a
classic supercell, except without the heavy precipitation core. LP storms often exhibit a
striking visual appearance; the main tower often is bell-shaped, with a corkscrew appearance
suggesting rotation. They are capable of producing tornadoes and very large hail. Radar
identification often is difficult relative to other types of supercells, so visual reports are very
important. LP storms almost always occur on or near the dry line, and thus are sometimes referred
to as dry line storms. Marine Small Craft Thunderstorm AdvisoryA marine warning issued by Environment Canada
Atmospheric Environment Branch when the possibility of thunderstorms is greater than 40
percent.Moderate Risk (of severe thunderstorms)Severe thunderstorms are expected to affect between 5 and
10 percent of the area. A moderate risk indicates the possibility of a significant severe weather episode. See
high risk, slight risk, convective outlook. Monitor 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. (Used if different from action stage, and at the discretion of the WFO or river forecast center [RFC].) The term "alert stage" is to be used instead of warning stage. Monitor stage or caution stage may be used instead of alert stage in some parts of the country. see/ alert stage/.Multicell ThunderstormThese thunderstorms are organized in clusters of at least 2-4 short-lived cells. Each cell generates a cold air outflow and these individual outflows combine to form a large gust front. Convergence along the gust front causes new cells to develop every 5 to 15 minutes. The cells move roughly with the mean wind. However, the area (storm) motion usually deviates significantly from the mean wind due to discrete propagation (new cell development) along the gust front. The multicellular nature of the storm is usually apparent on radar with multiple reflectivity cores and maximum tops.Multiple Vortex TornadoA tornado in which two or more condensation funnels or debris clouds are present at the same time, often rotating about a common center or about each other. Multiple-vortex tornadoes can be especially damaging.National Severe Storms LaboratoryThis is one of NOAA's internationally known Environmental Research Laboratories, leading the way in investigations of all aspects of severe weather. Headquartered in Norman OK with staff in Colorado, Nevada, Washington, Utah, and Wisconsin, the people of NSSL, in partnership with the National Weather Service, are dedicated to improving severe weather warnings and forecasts in order to save lives and reduce property damage.Nocturnal ThunderstormsThunderstorms which develop after sunset. They are often associated with the strengthening of the low level jet and are most common over the Plains states. They also occur over warm water and may be associated with the seaward extent of the overnight land breeze.Particle Trajectory ModelA computer sub-model that tracks the trajectories of multiple particles that are released into an atmospheric flow model.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.Post-storm ReportA report issued by a local National Weather Service office summarizing the impact of a tropical cyclone on it's forecast area. These reports include information on observed winds, pressures, storm surges, rainfall, tornadoes, damage and casualties.Probability of ThunderstormsThe probability based on climatology that a thunderstorm will be reported at that location during a specified period of time.Pulse Severe ThunderstormsSingle cell thunderstorms which produce brief periods of severe weather (3/4 inch hail, wind gusts in the excess of 58 miles an hour, or a tornado). Pulse StormA thunderstorm within which a brief period (pulse) of strong updraft occurs, during and immediately after which the storm produces a short episode of severe weather. These storms generally are not tornado producers, but often produce large hail and/or damaging winds. See also overshooting top.Radar Product Generator (RPG)The RPG is the computer in the NEXRAD system that receives polar-coordinate base radar data from the RDA and processes these data into end-user products. Algorithms are utilized for pattern-recognition, rainfall estimation, computation of VIL and other products. The RPG communicates these products to end-users. A specific subset of available products is always generated for the NIDS vendors for distribution outside of the NWS, DoD, and FAA. Other products are generated by the RPG upon request from a PUP.Radar Reflectivity Factor (z)z = the sum (over i) of (N_i * D_i^6), where N_i is the number of drops of diameter D_i in a pulse resolution volume. Note that z may be expressed in linear or logarithmic units. The radar reflectivity factor is simply a more meteorologically meaningful way of expressing the radar reflectivity.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.Reflectivity FactorThe result of a mathematical equation (called the Weather Radar Equation) that converts the analog power (in Watts) received by the radar antenna into a more usable quantity. The reflectivity factor (denoted by Z) takes into account several factors, including the distance of a target from the radar, the wavelength of the transmitted radiation, and certain assumptions about the kind and size of targets detected by the radar. The reflectivity factor ranges over several orders of magnitudes, so it is usually expressed on a logarithmic scale called dBZ (decibels of reflectivity).Rotor CloudA turbulent altocumulus cloud formation found in the lee of some mountain barriers when winds cross the barrier at high speed. The air in the cloud rotates around an axis parallel to the range. Also called a roll cloud.SandstormParticles of sand carried aloft by strong wind. The sand particles are mostly confined to the lowest ten feet, and rarely rise more than fifty feet above the ground.Sector BoundaryIn solar-terrestrial terms, in the solar wind, the area of demarcation between sectors, which are large-scale features distinguished by the predominant direction of the interplanetary magnetic field, toward or away from the sun.Sector VisibilityThe visibility in a specific direction that represents at least a 45º arc of a horizontal circle.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. Severe ThunderstormA thunderstorm that produces a tornado, winds of at least 58 mph (50knots), and/or hail at least 1" in diameter. Structural wind damage mayimply the occurrence of a severe thunderstorm. A thunderstorm wind equalto or greater than 40 mph (35 knots) and/or hail of at least 1" isdefined as approaching severe.Severe Thunderstorm WarningThis is issued when either a severe thunderstorm is indicated by the WSR-88D radar or a spotter reports a thunderstorm producing hail one inch or larger in diameter and/or winds equal or exceed 58 miles an hour; therefore, people in the affected area should seek safe shelter immediately. Severe thunderstorms can produce tornadoes with little or no advance warning. Lightning frequency is not a criteria for issuing a severe thunderstorm warning. They are usually issued for a duration of one hour. They can be issued without a Severe Thunderstorm Watch being already in effect.
Like a Tornado Warning, the Severe Thunderstorm Warning is issued by your National Weather Service Forecast Office (NWFO). Severe Thunderstorm Warnings will include where the storm was located, what towns will be affected by the severe thunderstorm, and the primary threat associated with the severe thunderstorm warning. If the severe thunderstorm will affect the nearshore or coastal waters, it will be issued as the combined product--Severe Thunderstorm Warning and Special Marine Warning. If the severe thunderstorm is also causing torrential rains, this warning may also be combined with a Flash Flood Warning. If there is an ampersand (&) symbol at the bottom of the warning, it indicates that the warning was issued as a result of a severe weather report.
After it has been issued, the affected NWFO will follow it up periodically with Severe Weather Statements. These statements will contain updated information on the severe thunderstorm and they will also let the public know when the warning is no longer in effect.Severe Thunderstorm WatchThis is issued by the National Weather Service when conditions are favorable for the development of severe thunderstorms in and close to the watch area. A severe thunderstorm by definition is a thunderstorm that produces one inch hail or larger in diameter and/or winds equal or exceed 58 miles an hour. The size of the watch can vary depending on the weather situation. They are usually issued for a duration of 4 to 8 hours. They are normally issued well in advance of the actual occurrence of severe weather. During the watch, people should review severe thunderstorm safety rules and be prepared to move a place of safety if threatening weather approaches.
A Severe Thunderstorm Watch is issued by the Storm Prediction Center in Norman, Oklahoma. Prior to the issuance of a Severe Thunderstorm Watch, SPC will usually contact the affected local National Weather Service Forecast Office (NWFO) and they will discuss what their current thinking is on the weather situation. Afterwards, SPC will issue a preliminary Severe Thunderstorm Watch and then the affected NWFO will then adjust the watch (adding or eliminating counties/parishes) and then issue it to the public by way of a Watch Redefining Statement. During the watch, the NWFO will keep the public informed on what is happening in the watch area and also let the public know when the watch has expired or been cancelled.Single Cell ThunderstormThis type of thunderstorm develops in weak vertical wind shear environments. On a hodograph, this would appear as a closely grouped set of random dots around the center of the graph. They are characterized by a single updraft core and a single downdraft that descends into the same area as the updraft. The downdraft and its outflow boundary then cut off the thunderstorm inflow. This causes the updraft and the thunderstorm to dissipate. Single cell thunderstorms are short-lived. They only last about 1/2 hour to an hour. These thunderstorms will occasionally become severe (3/4 inch hail, wind gusts in the excess of 58 miles an hour, or a tornado), but only briefly. In this case, they are called Pulse Severe Thunderstorms. SITOR(SImplex Teletype Over Radio) - a means of transmitting text broadcasts over radio. The U.S. Coast Guard SITOR broadcast of NWS forecasts is performed in mode B, FEC. SITOR is also known as Narrow Band Direct Printing (NBDP). SITOR/NBDP is an automated direct service similar to NAVTEX, but does not offer all of the same functionality such as avoiding repeated messages.Solar Sector Boundary (SSB)In solar-terrestrial terms, the apparent solar origin, or base, of the interplanetary sector boundary marked by the larger-scale polarity inversion lines.Splitting StormA 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.StormAny 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 to tropical cyclones to synoptic-scale extratropical cyclones.Storm DataThis National Climatic Data Center (NCDC) monthly publication documents a chronological listing, by states, of occurrences of storms and unusual weather phenomena. Reports contain information on storm paths, deaths, injuries, and property damage. An "Outstanding storms of the month" section highlights severe weather events with photographs, illustrations, and narratives. The December issue includes annual tornado, lightning, flash flood, and tropical cyclone summaries.Storm MotionThe speed and direction at which a thunderstorm travels.Storm RelativeMeasured relative to a moving thunderstorm, usually referring to winds, wind shear, or helicity.Storm Relative Mean Radial Velocity Map(SRM): This WSR-88D radar product depicts a full 360º sweep of radial velocity data with the average motion of all identified storms subtracted out. 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 Regi(SRR): This WSR-88D radar product depicts a 27
nm by 27 nm region of storm relative mean radial velocity centered on a point which the operator
can specify anywhere within a 124 nm radius of the radar. The storm motion subtracted defaults to
the motion of the storm closest to the product center, or can be input by the operator. It is used to
examine the 3-dimensional storm relative flow of a specific thunderstorm (radar operator centers
product on a specific thunderstorm; aid in displaying shear and rotation in thunderstorms and
storm top divergence that might otherwise be obscured by storm motion; and gain higher
resolution velocity productStorm ScaleReferring to weather systems with sizes on the order of individual thunderstorms. See synoptic scale and mesoscale.Storm SurgeAn abnormal rise in sea level accompanying a hurricane or other intense storm, whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic tide from the observed storm tide.Storm TideThe actual level of sea water resulting from the astronomic tide combined with the storm surge. Most NWS flood statements, watches, or warnings quantifying above-normal tides will report the Storm Tide.Storm Total PrecipitationThis radar image is an estimate of accumulated rainfall since the last time there was a one-hour, or more, break in precipitation. It is used to locate flood potential over urban or rural areas, estimate total basin runoff and provide rainfall accumulations for the duration of the event and is available only for the short range (out to 124 nm). To determine accumulated precipitation at greater distances you should link to an adjacent radar. Storm Tracking InformationThis WSR-88D radar product displays the previous, current, and projected locations of storm centroids (forecast and past positions are limited to one hour or less). Forecast tracks are based upon linear extrapolation of past storm centroid positions, and they are intended for application to individual thunderstorms not lines or clusters. It is used to provide storm movement: low track variance and/or 2 or more plotted past positions signify reliable thunderstorm movement.Storm WarningA warning of sustained surface winds, or frequent gusts, in the range of 48 knots (55 mph) to 63 knots (73 mph) inclusive, either predicted or occurring, and not directly associated with a tropical cyclone. Storm WatchA watch for an increased risk of a storm force wind event for sustained surface winds, or frequent gusts, of 48 knots (55 mph) to 63 knots (73 mph), but its occurrence, location, and/or timing is still uncertain. Stormwater DischargeIn hydrologic terms, precipitation that does not infiltrate into the ground or evaporate due to impervious land surfaces but instead flows onto adjacent
land or water areas and is routed into drain/sewer systems.Subsurface Storm FlowIn hydrologic terms, 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.Subtropical StormA subtropical cyclone in which the maximum 1-minute sustained surface wind is 34 knots (39 mph) or more. Supercell ThunderstormPotentially the most dangerous of the convective storm types. Storms possessing this structure have been observed to generate the vast majority of long-lived strong and violent (F2-F5) tornadoes, as well as downburst damage and large hail. It is defined as a thunderstorm consisting of one quasi-steady to rotating updraft which may exist for several hours. Supercells usually move to the right of the mean wind. These are called "Right Movers" and they are favored with veering winds. Occasionally, these thunderstorms will move to the left of the mean wind. These thunderstorms are called "Left Movers". These supercells typically don't last as long as their "Right Mover" cousins and they usually only produce large hail (greater than 3/4 inch in diameter) and severe wind gusts in the excess of 58 miles an hour. Left Movers are favored when you have backing winds.
Radar will observe essentially one long-lived cell, but small perturbations to the cell structure may be evident. The stronger the updraft, the better the chance that the supercell will produce severe (hail greater than 3/4 inch in diameter, wind gusts greater than 58 miles an hour, and possibly a tornado) weather.
Severe supercell development is most likely in an environment possessing great buoyancy (CAPE) and large vertical wind shear. A Bulk Richardson Number of between 15 and 35 favor supercell development. Typically, the hodograph will look like a horse shoe. This is due to the wind speed increasing rapidly with height and the wind direction either veering or backing rapidly with height.ThermistorA resistor whose resistance changes with temperature. Because of the known dependence of resistance on temperature, the resistor can be used as a temperature sensor.ThunderstormA local storm produced by a cumulonimbus cloud and accompanied by lightning and thunder.Tilted StormA thunderstorm or cloud tower which is not purely vertical but instead exhibits a slanted or tilted character. It is a sign of vertical wind shear, a favorable condition for severe storm development.TORTornado (or) Tornado WarningTornadoA violently rotating column of air, usually pendant to a cumulonimbus, with circulation reaching the ground. It nearly always starts as a funnel cloud and may be accompanied by a loud roaring noise. On a local scale, it is the most destructive of all atmospheric phenomena.Tornado EmergencyAn exceedingly rare tornado warning issued when there is a severe threat to human life and catastrophic damage from an imminent or ongoing tornado. This tornado warning is reserved for situations when a reliable source confirms a tornado, or there is clear radar evidence of the existence of a damaging tornado, such as the observation of debris.Tornado FamilyA series of tornadoes produced by a single supercell, resulting in damage path segments
along the same general line.Tornado Vortex SignatureAn image of a tornado on the Doppler radar screen that shows up as a small region of rapidly changing wind speeds inside a mesocyclone. The following velocity criteria is normally required for recognition: velocity difference between maximum inbound and outbound (shear) is greater than or equal to 90 knots at less than 30 nmi and is greater than or equal to 70 knots between 30 and 55 nmi. It shows up as a red upside down triangle on the Storm Relative Velocity Display. Existence of a TVS strongly increases the probability of tornado occurrence, but does not guarantee it; therefore, the feature triggering it must be examined closely by the radar operator. A TVS is not a visually observable feature.Tornado WarningThis is issued when a tornado is indicated by the WSR-88D radar or sighted by spotters; therefore, people in the affected area should seek safe shelter immediately. They can be issued without a Tornado Watch being already in effect. They are usually issued for a duration of around 30 minutes.
A Tornado Warning is issued by your local National Weather Service office (NWFO). It will include where the tornado was located and what towns will be in its path. If the tornado will affect the nearshore or coastal waters, it will be issued as the combined product--Tornado Warning and Special Marine Warning. If the thunderstorm which is causing the tornado is also producing torrential rains, this warning may also be combined with a Flash Flood Warning. If there is an ampersand (&) symbol at the bottom of the warning, it indicates that the warning was issued as a result of a severe weather report.
After it has been issued, the affected NWFO will followed it up periodically with Severe Weather Statements. These statements will contain updated information on the tornado and they will also let the public know when warning is no longer in effect.Tornado WatchThis is issued by the National Weather Service when conditions are favorable for the development of tornadoes in and close to the watch area. Their size can vary depending on the weather situation. They are usually issued for a duration of 4 to 8 hours. They normally are issued well in advance of the actual occurrence of severe weather. During the watch, people should review tornado safety rules and be prepared to move a place of safety if threatening weather approaches.
A Tornado Watch is issued by the Storm Prediction Center (SPC) in Norman, Oklahoma. Prior to the issuance of a Tornado Watch, SPC will usually contact the affected local National Weather Forecast Office (NWFO) and they will discuss what their current thinking is on the weather situation. Afterwards, SPC will issue a preliminary Tornado Watch and then the affected NWFO will then adjust the watch (adding or eliminating counties/parishes) and then issue it to the public. After adjusting the watch, the NWFO will let the public know which counties are included by way of a Watch Redefining Statement. During the watch, the NWFO will keep the public informed on what is happening in the watch area and also let the public know when the watch has expired or been cancelled.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.United States Drought Monitor (USDM)A multi-agency product that defines and highlights the severity of drought across the ConUS and OConUS based on expert interpretation of a multitude of indices.VVSTORMModel-based convection algorithm.Warm SectorA region of warm surface air between a cold front and a warm front.Wedge TornadoSlang for a large tornado with a condensation funnel that is at least as wide (horizontally) at the ground as it is tall (vertically) from the ground to cloud base. The term "wedge" often is used somewhat loosely to describe any large tornado. However, not every large tornado is a wedge. A true wedge tornado, with a funnel at least as wide at the ground as it is tall, is very rare.
Wedges often appear with violent tornadoes (F4 or F5 on the Fujita Scale), but many documented wedges have been rated lower. And some violent tornadoes may not appear as wedges (e.g., Xenia, OH on 3 April 1974, which was rated F5 but appeared only as a series of suction vortices without a central condensation funnel). Whether or not a tornado achieves "wedge" status depends on several factors other than intensity - in particular, the height of the environmental cloud base and the availability of moisture below cloud base. Therefore, spotters should not estimate wind speeds or F-scale ratings based on visual appearance alone. However, it generally is safe to assume that most (if not all) wedges have the potential to produce strong (F2/F3) or violent (F4/F5) damage.Wind Chill FactorIncreased wind speeds accelerate heat loss from exposed skin. No specific rules exist for determining when wind chill becomes dangerous. As a general rule, the threshold for potentially dangerous wind chill conditions is about -20°F.Winter Storm WarningThis product is issued by the National Weather Service when a winter storm is producing or is forecast to produce heavy snow or significant ice accumulations. The criteria for this warning can vary from place to place.Winter Storm WatchThis product is issued by the National Weather Service when there is a potential for heavy snow or significant ice accumulations, usually at least 24 to 36 hours in advance. The criteria for this watch can vary from place to place.
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