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77-705: First Warning is the name of a severe weather warning system designed for broadcast television stations, typically those in the United States. A weather advisory product based on First Warning, called First Alert , is an automated version of this product, which has come into widespread use by television stations and is marketed under different names depending on the graphics service vendor. Both products are typically used by television stations that have an in-house news and weather operation, although some television stations that do not broadcast news at all or have their newscasts produced by another station in their market may use

154-403: A complete Canadian Doppler network between 1998 and 2004. France and other European countries had switched to Doppler networks by the early 2000s. Meanwhile, rapid advances in computer technology led to algorithms to detect signs of severe weather, and many applications for media outlets and researchers. After 2000, research on dual polarization technology moved into operational use, increasing

231-483: A legend with colored text, in text beside a colored key or in text inside a colored line bar. Each watch, warning or advisory is assigned a color code and arranged in order of urgency (with tornado warnings being given the highest priority of all alerts). However, while virtually all First Warning systems may display the same color for severe thunderstorm watches (blue), severe thunderstorm warnings (yellow or orange), tornado watches (green) and tornado warnings (red),

308-522: A multi-tier impact-based warning (IBW) system of impact statements to notify the public and emergency management officials of the severity of specific severe weather phenomena. The impact statement system—initially used only for tornado and severe thunderstorm warnings—was first employed by the WFOs in Wichita and Topeka, Kansas , and Springfield , St. Louis and Kansas City / Pleasant Hill, Missouri beginning with

385-471: A per-county basis rather than delineating them by polygons . This system's on-air design element is stylized depending on the television station using it (for example, until an upgrade of its system to allow widescreen overlays during broadcasts of high definition programming in March 2009, Oklahoma City NBC affiliate KFOR-TV 's 4WARN Storm Alert variant displayed an "L"-bar surrounding a resized box display of

462-455: A rough outline of the Gulf of Mexico on a transparent sheet of plastic. During the broadcast, he held that transparent overlay over the computer's black-and-white radar display to give his audience a sense both of Carla's size and of the location of the storm's eye. This made Rather a national name and his report helped in the alerted population accepting the evacuation of an estimated 350,000 people by

539-417: A separate wind advisory or warning if a Blizzard warning is already in effect. However, as seen with Hurricane Sandy , if widespread high wind warnings are in effect prior to the issuance of a blizzard warning, the high wind warnings may be continued. * Tropical Storm Warning flags and lights will always be displayed the same as Storm Warning flags and lights. † A tropical storm with winds in this range

616-401: A timely and convenient manner. The original version of this forecast product required manual input of weather alerts into the computer system by a meteorologist, with the specific advisory information, the counties/parishes listed in the alert and the advisory type. ABC affiliate KOCO-TV , a market competitor to KWTV, created an automated version of this product called First Alert (a name

693-486: A tornado devastated Union City, Oklahoma , just west of Oklahoma City . For the first time, a Dopplerized 10 cm wavelength radar from NSSL documented the entire life cycle of the tornado. The researchers discovered a mesoscale rotation in the cloud aloft before the tornado touched the ground – the tornadic vortex signature . NSSL's research helped convince the National Weather Service that Doppler radar

770-832: A verbal report increase with the severity of the returns. For example, the U.S. National NEXRAD radar sites use the following scale for different levels of reflectivity: Strong returns (red or magenta) may indicate not only heavy rain but also thunderstorms, hail, strong winds, or tornadoes, but they need to be interpreted carefully, for reasons described below. When describing weather radar returns, pilots, dispatchers, and air traffic controllers will typically refer to three return levels: Aircraft will try to avoid level 2 returns when possible, and will always avoid level 3 unless they are specially-designed research aircraft. Some displays provided by commercial television outlets (both local and national) and weather websites, like The Weather Channel and AccuWeather , show precipitation types during

847-464: Is a type of radar used to locate precipitation , calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pulse-Doppler radars , capable of detecting the motion of rain droplets in addition to the intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather . During World War II, radar operators discovered that weather

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924-401: Is called the radial Doppler velocity because it gives only the radial variation of distance versus time between the radar and the target. The real speed and direction of motion has to be extracted by the process described below. The phase between pulse pairs can vary from - π {\displaystyle \pi } and + π {\displaystyle \pi } , so

1001-479: Is even incorporated into numerical weather prediction models to improve analyses and forecasts. During World War II, military radar operators noticed noise in returned echoes due to rain, snow, and sleet . After the war, military scientists returned to civilian life or continued in the Armed Forces and pursued their work in developing a use for those echoes. In the United States, David Atlas at first working for

1078-564: Is likely. Alternate wording: Alternate wording: Hazardous weather forecasts and alerts are provided to the public using the NOAA Weather Radio All Hazards system and through news media such as television , radio and internet sources. Many local television stations have overlay graphics which will either show a map or a list of the affected areas. The most common NWS weather alerts to be broadcast over NOAA Weather Radio using SAME technology are described in

1155-408: Is on the order of a millisecond , which is a thousand times longer than the pulse duration. The length of this phase is determined by the need for the microwave radiation (which travels at the speed of light ) to propagate from the detector to the weather target and back again, a distance which could be several hundred kilometers. The horizontal distance from station to target is calculated simply from

1232-402: Is received power, P t {\displaystyle \scriptstyle P_{t}} is transmitted power, G {\displaystyle \scriptstyle G} is the gain of the transmitting/receiving antenna, λ {\displaystyle \scriptstyle \lambda } is radar wavelength, σ {\displaystyle \scriptstyle \sigma }

1309-687: Is sometimes referred to as a "severe tropical storm". ‡ The Extreme Wind Warning is issued shortly before the eyewall makes landfall The various weather conditions described above have different levels of risk. The National Weather Service uses a multi-tier system of weather statements to notify the public of threatening weather conditions. These statements are used in conjunction with specific weather phenomena to convey different levels of risk. In order of increasing risk, these statements are: The Storm Prediction Center (SPC) issues Day 1, Day 2, and Day 3 Convective Outlooks depicting forecast areas of general (non-severe) and severe thunderstorm threats across

1386-413: Is the beam width (in radians). This formula assumes the beam is symmetrically circular, "r" is much greater than "h" so "r" taken at the beginning or at the end of the pulse is almost the same, and the shape of the volume is a cone frustum of depth "h". Between each pulse, the radar station serves as a receiver as it listens for return signals from particles in the air. The duration of the "listen" cycle

1463-480: Is the beam width in radians. In combining the two equations: Which leads to: The return varies inversely to R 2 {\displaystyle \,R^{2}} instead of R 4 {\displaystyle \,R^{4}} . In order to compare the data coming from different distances from the radar, one has to normalize them with this ratio. Return echoes from targets (" reflectivity ") are analyzed for their intensities to establish

1540-454: Is the radar cross section of the target and R {\displaystyle \scriptstyle R} is the distance from transmitter to target. In this case, the cross sections of all the targets must be summed: where c {\displaystyle \,c} is the light speed, τ {\displaystyle \,\tau } is temporal duration of a pulse and θ {\displaystyle \,\theta }

1617-406: Is traversing is larger for areas farther away from the station, and smaller for nearby areas, decreasing resolution at farther distances. At the end of a 150 – 200 km sounding range, the volume of air scanned by a single pulse might be on the order of a cubic kilometer. This is called the pulse volume . The volume of air that a given pulse takes up at any point in time may be approximated by

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1694-400: Is used only for short-range units, and 1 cm Ka-band weather radar is used only for research on small-particle phenomena such as drizzle and fog. W band (3 mm) weather radar systems have seen limited university use, but due to quicker attenuation, most data are not operational. Radar pulses diverge as they move away from the radar station. Thus the volume of air that a radar pulse

1771-554: The Air Force and later for MIT , developed the first operational weather radars. In Canada, J.S. Marshall and R.H. Douglas formed the "Stormy Weather Group" in Montreal. Marshall and his doctoral student Walter Palmer are well known for their work on the drop size distribution in mid-latitude rain that led to understanding of the Z-R relation, which correlates a given radar reflectivity with

1848-648: The Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA), a multidisciplinary, multi-university collaboration of engineers, computer scientists, meteorologists, and sociologists to conduct fundamental research, develop enabling technology, and deploy prototype engineering systems designed to augment existing radar systems by sampling the generally undersampled lower troposphere with inexpensive, fast scanning, dual polarization, mechanically scanned and phased array radars. In 2023,

1925-823: The United States Geological Survey ( Aviation Color Codes ). VAAs are standardized worldwide by the International Civil Aviation Organization . The National Weather Service also relays messages for non-weather related hazardous events in text products and NOAA Weather Radio broadcasts: Wind alerting is classified into groups of two Beaufort numbers, beginning at 6–7 for the lowest class of wind advisories. The last group includes three Beaufort numbers, 14–16. The actual alerts can be categorized into three classes: maritime wind warnings, land wind warnings, and tropical cyclone warnings . Advisory-force and gale-force winds will not trigger

2002-760: The 2012 Spring severe weather season, eventually expanded to include 33 additional National Weather Service Weather Forecast Offices within the Central Region Headquarters in 2013, and then to eight additional offices within the Eastern, Southern and Western Regions in the spring of 2014. Since July 28, 2021 (or as late as August 2 in certain County Warning Areas), the NWS has incorporated categorical “CONSIDERABLE” and “DESTRUCTIVE" damage threat indicators (similar to those incorporated into tornado warning products since

2079-468: The Earth is round, the radar beam in vacuum would rise according to the reverse curvature of the Earth. However, the atmosphere has a refractive index that diminishes with height, due to its diminishing density. This bends the radar beam slightly toward the ground and with a standard atmosphere this is equivalent to considering that the curvature of the beam is 4/3 the actual curvature of the Earth. Depending on

2156-575: The NWS and its sub-organizations (some of which may be specific to certain cities or regions). Related weather scales and general weather terms used by the agency are also addressed. The NWS divides severe weather alerts into several types of hazardous/hydrologic events: The following advisories are issued by the National Weather Service Aviation Weather Center (outside of Alaska) or Alaska Aviation Weather Unit. Atmospheric ash plume advisories/warnings are also issued by

2233-468: The U.S. National Oceanic and Atmospheric Administration has been experimenting with phased-array radar as a replacement for conventional parabolic antenna to provide more time resolution in atmospheric sounding . This could be significant with severe thunderstorms, as their evolution can be better evaluated with more timely data. Also in 2003, the National Science Foundation established

2310-508: The United States was in September 1961. As Hurricane Carla was approaching the state of Texas, local reporter Dan Rather , suspecting the hurricane was very large, took a trip to the U.S. Weather Bureau WSR-57 radar site in Galveston in order to get an idea of the size of the storm. He convinced the bureau staff to let him broadcast live from their office and asked a meteorologist to draw him

2387-680: The United States. Instead, the Saffir–Simpson hurricane scale (Category 1, Category 2, etc.) is used. The Enhanced Fujita scale , an updated version of the original Fujita scale that was developed by Ted Fujita with Allen Pearson , assigns a numerical rating from EF0 to EF5 to rate the damage intensity of tornadoes . EF0 and EF1 tornadoes are considered "weak" tornadoes, EF2 and EF3 are classified as "strong" tornadoes, with winds of at least major hurricane force, where EF4 and EF5 are categorized as "violent" tornadoes, with winds corresponding to category 5 hurricane winds and rising to match or exceed

First Warning - Misplaced Pages Continue

2464-429: The alert product including the date and time of issuance, SAME county codes and other text coding that precedes and follows the main body of the alert product. First Warning is commonly displayed on-air in the form of a map of an entire state or the specific counties representing a television station's viewing area (which may cover one or more states) with a list of the watches, warnings or advisories either displayed as

2541-491: The amount of information available on precipitation type (e.g. rain vs. snow). "Dual polarization" means that microwave radiation which is polarized both horizontally and vertically (with respect to the ground) is emitted. Wide-scale deployment was done by the end of the decade or the beginning of the next in some countries such as the United States, France, and Canada. In April 2013, all United States National Weather Service NEXRADs were completely dual-polarized. Since 2003,

2618-469: The amount of time that elapses from the initiation of the pulse to the detection of the return signal. The time is converted into distance by multiplying by the speed of light in air: where c = 299,792.458 km/s is the speed of light , and n ≈ 1.0003 is the refractive index of air. If pulses are emitted too frequently, the returns from one pulse will be confused with the returns from previous pulses, resulting in incorrect distance calculations. Since

2695-496: The authorities, which was the largest evacuation in US history at that time. Just 46 people were killed thanks to the warning and it was estimated that the evacuation saved several thousand lives, as the smaller 1900 Galveston hurricane had killed an estimated 6000-12000 people. During the 1970s, radars began to be standardized and organized into networks. The first devices to capture radar images were developed. The number of scanned angles

2772-466: The color codes for other warnings or advisories may vary depending on the station (in some cases, the color code for one watch/warning/advisory may match that of another). When a watch, warning or advisory (severe or non-severe) is disseminated by either the Storm Prediction Center (SPC) or a local National Weather Service Weather Forecast Office, a scroll with text moving right to left across

2849-409: The contiguous United States, along with a text narrative discussion consisting of a plain-language summary of the threat type(s) and timing focused on areas of highest risk, and a technical discussion written in scientific language that usually includes a synoptic overview of convective patterns as well as, if necessary, a geographically specific narrative of meteorological reasoning and justification for

2926-406: The current program, containing a map of all 77 Oklahoma counties and accompanying legend, along with the name of a specific county above it – the country referenced in the assigned warning/watch color on the map is shown blinking for three seconds – and a ticker on the upper third of the screen; a live display of the station's Doppler radar system replaced the alert map when the alert ticker scrolled

3003-448: The droplets or ice particles of interest, because Rayleigh scattering occurs at these frequencies. This means that part of the energy of each pulse will bounce off these small particles, back towards the radar station. Shorter wavelengths are useful for smaller particles, but the signal is more quickly attenuated. Thus 10 cm ( S-band ) radar is preferred but is more expensive than a 5 cm C-band system. 3 cm X-band radar

3080-418: The elevation angle of the antenna and other considerations, the following formula may be used to calculate the target's height above ground: where: A weather radar network uses a series of typical angles that are set according to its needs. After each scanning rotation, the antenna elevation is changed for the next sounding. This scenario will be repeated on many angles to scan the entire volume of air around

3157-482: The following table: The NWS uses several scales in describing weather events or conditions. Several common scales are described below. The size of individual hailstones that reach surface level is determined by speed of the updraft which create the individual ice crystals at atmospheric levels. Larger hailstones are capable of producing damage to property, and particularly with very large hailstones, resulting in serious injury or death due to blunt-force trauma induced by

First Warning - Misplaced Pages Continue

3234-446: The formula v = h r 2 θ 2 {\displaystyle \,{v=hr^{2}\theta ^{2}}} , where v is the volume enclosed by the pulse, h is pulse width (in e.g. meters, calculated from the duration in seconds of the pulse times the speed of light), r is the distance from the radar that the pulse has already traveled (in e.g. meters), and θ {\displaystyle \,\theta }

3311-887: The general public and special interests through a collection of national and regional guidance centers (including the Storm Prediction Center , the National Hurricane Center and the Aviation Weather Center), and 122 local Weather Forecast Offices (WFO). Each Weather Forecast Office is assigned a designated geographic area of responsibility—also known as a county warning area —that are split into numerous forecast zones (encompassing part or all of one county or equivalent thereof ) for issuing forecasts and hazardous weather products. The article primarily defines precise meanings and associated criteria for nearly all weather warnings, watches, advisories, statements, and other products not associated with hazardous weather issued by

3388-444: The impact of the hailstones. Hailstone size is typically correspondent to the size of an object for comparative purposes. * Begins hail sizes within the severe hail criterion. † Begins hail sizes within the Storm Prediction Center 's significant severe criterion. The Beaufort scale is an empirical measure that correlates wind speed to observed conditions at sea or on land. :Beaufort levels above 12 are non-standard in

3465-615: The implementation of the Impact Based Warning system) at the bottom of the product text of certain severe thunderstorm warnings and related Severe Weather Statements to indicate higher-end hail and/or wind events caused by the parent storm cell. Under this system, the warning product will include text denoting the specific hazard (i.e., 60 mph wind gusts and quarter size hail) and applicable sourcing (either via indication from Doppler weather radar, or visual confirmation from storm spotters or other emergency management officials) and

3542-523: The intensities of their sustained winds. The scale spans from Category 1 (winds of at least 74 miles per hour (119 km/h)) to Category 5 (exceeding 156 miles per hour (251 km/h)). Unlike the Enhanced Fujita Scale, which assigns ratings for tornadoes after damage has been incurred and thoroughly assessed, categories on the Saffir-Simpson scale are assigned to most active cyclones that reach

3619-458: The jurisdiction. As many television stations had not upgraded their master control infrastructures to allow high definition broadcasts of non-network programs or the hardware for the First Warning system to be compatible with HD broadcasts prior to the late 2000s and early 2010s, the high definition program feed would often be downconverted to standard definition when the map/ticker graphic

3696-700: The level of impact to life and/or property. In order of increasing risk by warning type, these statements—which may be modified at the discretion of the regional forecast office—are: (For landspouts and weak tornadoes, alternative impact statements may be utilized at the discretion of the Weather Forecast Office; all other statements are standard nationwide.) Alternate wording: (This alternate damage impact statement should include both aforementioned statements.) Alternate wording: Alternate wording: Alternate wording: Alternate wording: Alternate wording: Damage to vehicles

3773-520: The level of overall severe thunderstorm risk via numbers, descriptive labeling, and colors as follows: (The Day 4-8 Convective Outlook assesses the percentile probability of severe thunderstorm activity during that period at the 15% and 30% likelihood.) Many of the National Weather Service's Weather Forecast Offices —primarily those located within the Central and Southern Region Headquarters—use

3850-960: The minimum hurricane threshold, even before landfall. 74–95 mph 64–82 knot 119–153 km/h 1.2–1.5 m 980 mbar Ismael (1995) Danny (1997) Gaston (2004) Kate (2015) 96–110 mph 83–95 kn 154–177 km/h 1.8–2.4 m 965–979 mbar Diana (1990) Erin (1995) Marty (2003) Juan (2003) 111–129 mph 96–113 kn 178–209 km/h 2.7–3.7 m 945–964 mbar Alicia (1983) Roxanne (1995) Fran (1996) Isidore (2002) Sandy (2012) 130–156 mph 114–135 kn 210–249 km/h 4.0–5.5 m 920–944 mbar Hazel (1954) Iniki (1992) Iris (2001) Harvey (2017) Laura (2020) Ian (2022) <920 mbar Camille (1969) Gilbert (1988) Andrew (1992) Wilma (2005) Irma (2017) Michael (2018) Dorian (2019) Doppler weather radar Weather radar , also called weather surveillance radar ( WSR ) and Doppler weather radar ,

3927-474: The position and intensity of precipitation, were incorporated by weather services around the world. The early meteorologists had to watch a cathode-ray tube . In 1953 Donald Staggs, an electrical engineer working for the Illinois State Water Survey, made the first recorded radar observation of a " hook echo " associated with a tornadic thunderstorm. The first use of weather radar on television in

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4004-499: The possibility to estimate the wind speed and direction where precipitation is present. A target's motion relative to the radar station causes a change in the reflected frequency of the radar pulse, due to the Doppler effect . With velocities of less than 70-metre/second for weather echos and radar wavelength of 10 cm, this amounts to a change only 0.1 ppm . This difference is too small to be noted by electronic instruments. However, as

4081-417: The precipitation rate in the scanned volume. The wavelengths used (1–10 cm) ensure that this return is proportional to the rate because they are within the validity of Rayleigh scattering which states that the targets must be much smaller than the wavelength of the scanning wave (by a factor of 10). Reflectivity perceived by the radar (Z e ) varies by the sixth power of the rain droplets' diameter (D),

4158-410: The private American company Tomorrow.io launched a Ka-band space-based radar for weather observation and forecasting. Weather radars send directional pulses of microwave radiation, on the order of one microsecond long, using a cavity magnetron or klystron tube connected by a waveguide to a parabolic antenna . The wavelengths of 1 – 10 cm are approximately ten times the diameter of

4235-407: The program does interpolations to produce an image with defined zones. These will include interpolation errors due to the calculation. Mesoscale variations of the precipitation zones will also be lost. More sophisticated programs use the numerical weather prediction output from models, such as NAM and WRF , for the precipitation types and apply it as a first guess to the radar echoes, then use

4312-577: The radar cannot "see" below the height above ground of the minimal angle (shown in green) or closer to the radar than the maximal one (shown as a red cone in the center). Because the targets are not unique in each volume, the radar equation has to be developed beyond the basic one. Assuming a monostatic radar where G t = A r ( o r G r ) = G {\displaystyle G_{t}=A_{r}(\mathrm {or} \,G_{r})=G} : where P r {\displaystyle \scriptstyle P_{r}}

4389-485: The radar within the maximum range. Usually, the scanning strategy is completed within 5 to 10 minutes to have data within 15 km above ground and 250 km distance of the radar. For instance in Canada, the 5 cm weather radars use angles ranging from 0.3 to 25 degrees. The accompanying image shows the volume scanned when multiple angles are used. Due to the Earth's curvature and change of index of refraction with height,

4466-399: The range from reflectivity at the expense of velocity range, or increasing the latter at the expense of range from reflectivity. In general, the useful range compromise is 100–150 km for reflectivity. This means for a wavelength of 5 cm (as shown in the diagram), an unambiguous velocity range of 12.5 to 18.75 metre/second is produced (for 150 km and 100 km, respectively). For

4543-567: The rate at which rainwater is falling. In the United Kingdom, research continued to study the radar echo patterns and weather elements such as stratiform rain and convective clouds , and experiments were done to evaluate the potential of different wavelengths from 1 to 10 centimeters. By 1950 the UK company EKCO was demonstrating its airborne 'cloud and collision warning search radar equipment'. Between 1950 and 1980, reflectivity radars, which measure

4620-523: The relative velocity of the particles in the air. In the United States, the construction of a network consisting of 10 cm radars, called NEXRAD or WSR-88D (Weather Surveillance Radar 1988 Doppler), was started in 1988 following NSSL's research. In Canada, Environment Canada constructed the King City station, with a 5 cm research Doppler radar, by 1985; McGill University dopplerized its radar ( J. S. Marshall Radar Observatory ) in 1993. This led to

4697-413: The screen featuring information on the alert appears, usually accompanied by a three or six brief bursts of a 1050 Hz attention signal that last between three and eight seconds. Although local offices of the National Weather Service have issued warnings for tornadoes and severe thunderstorms based on the path of a storm since October 2007, most stations using the system display the affected jurisdictions on

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4774-555: The screen). The on-screen display is usually removed before the broadcast of a severe weather cut-in or commercial break; the length of time it is displayed may also be truncated if no significant weather is imminent in the viewing area. Additional features were added to First Warning and its variants during the 2000s, including functions allowing the map to toggle between displays of current weather alerts and live or looped radar imagery, including radar images by individual county, which are often accompanied by warning information specific to

4851-421: The second time). In some areas, the First Warning map is displayed on the top left or right portion of the screen to avoid obstructing the rest of the program or closed captions elsewhere on-screen (though the latter purpose is somewhat defeated by the fact that closed captions occasionally appear at the top of the screen, while in turn, the map may obstruct visual aspects of the program in its positioned area of

4928-408: The square of the dielectric constant (K) of the targets and the drop size distribution (e.g. N[D] of Marshall-Palmer ) of the drops. This gives a truncated Gamma function , of the form: Precipitation rate (R), on the other hand, is equal to the number of particles, their volume and their fall speed (v[D]) as: So Z e and R have similar functions that can be resolved by giving a relation between

5005-440: The station has since used for its doppler radar system, now known as "Advantage Doppler HD", and which the station currently uses as its weather branding), in which the weather information is updated by the computer itself, delivered by communication routes wired to media outlets from the National Weather Service . Tornado sirens are also usually activated for the affected areas if present. and parses out additional text included in

5082-429: The strongest tropical cyclones on record. The EF scale is based on tornado damage (primarily to buildings), which makes it difficult to rate tornadoes that strike in sparsely populated areas, where few man-made structures are found. The Enhanced Fujita scale went into effect on February 1, 2007. The Saffir–Simpson hurricane wind scale , assigns a numerical classification of hurricanes into five categories distinguished by

5159-424: The surface data for final output. Until dual-polarization (section Polarization below) data are widely available, any precipitation types on radar images are only indirect information and must be taken with care. Precipitation is found in and below clouds. Light precipitation such as drops and flakes is subject to the air currents, and scanning radar can pick up the horizontal component of this motion, thus giving

5236-570: The system as well. First Warning was created in 1990 by Gary England , then the chief meteorologist of CBS affiliate KWTV in Oklahoma City , Oklahoma (a city which historically has had the highest number of tornado strikes of any U.S. city since tornado records began to be logged in 1890), and went into use in the spring of 1991. The system was conceived to provide visual alerts for severe and winter weather as well as other hydrologic and non-hydrologic weather advisories to television viewers in

5313-1553: The targets move slightly between each pulse, the returned wave has a noticeable phase difference or phase shift from pulse to pulse. Doppler weather radars use this phase difference (pulse pair difference) to calculate the precipitation's motion. The intensity of the successively returning pulse from the same scanned volume where targets have slightly moved is: I = I 0 sin ⁡ ( 4 π ( x 0 + v Δ t ) λ ) = I 0 sin ⁡ ( Θ 0 + Δ Θ ) { x = distance from radar to target λ = radar wavelength Δ t = time between two pulses {\displaystyle I=I_{0}\sin \left({\frac {4\pi (x_{0}+v\Delta t)}{\lambda }}\right)=I_{0}\sin \left(\Theta _{0}+\Delta \Theta \right)\quad {\begin{cases}x={\text{distance from radar to target}}\\\lambda ={\text{radar wavelength}}\\\Delta t={\text{time between two pulses}}\end{cases}}} So Δ Θ = 4 π v Δ t λ {\displaystyle \Delta \Theta ={\frac {4\pi v\Delta t}{\lambda }}} , v = target speed = λ Δ Θ 4 π Δ t {\displaystyle {\frac {\lambda \Delta \Theta }{4\pi \Delta t}}} . This speed

5390-434: The two of the form called Z-R relation : Where a and b depend on the type of precipitation (snow, rain, convective or stratiform ), which has different Λ {\displaystyle \Lambda } , K, N 0 and v. Radar returns are usually described by colour or level. The colours in a radar image normally range from blue or green for weak returns, to red or magenta for very strong returns. The numbers in

5467-457: The type of coverage and intensity applicable to the severe thunderstorm threat. The categorical forecast in the Day 1-3 Convective Outlooks—which estimates a severe weather event occurring within 25 miles (40 km) of a point and derives the attendant risk areas from probability forecasts of tornadoes, damaging winds, and large hail on Days 1 and 2, and a combined severe weather risk on Day 3—specifies

5544-455: The unambiguous Doppler velocity range is This is called the Nyquist velocity. This is inversely dependent on the time between successive pulses: the smaller the interval, the larger is the unambiguous velocity range. However, we know that the maximum range from reflectivity is directly proportional to Δ t {\displaystyle \Delta t} : The choice becomes increasing

5621-531: The winter months: rain, snow, mixed precipitations ( sleet and freezing rain ). This is not an analysis of the radar data itself but a post-treatment done with other data sources, the primary being surface reports ( METAR ). Over the area covered by radar echoes, a program assigns a precipitation type according to the surface temperature and dew point reported at the underlying weather stations . Precipitation types reported by human operated stations and certain automatic ones ( AWOS ) will have higher weight. Then

5698-470: Was a crucial forecasting tool. The Super Outbreak of tornadoes on 3–4 April 1974 and their devastating destruction might have helped to get funding for further developments. Between 1980 and 2000, weather radar networks became the norm in North America, Europe, Japan and other developed countries. Conventional radars were replaced by Doppler radars, which in addition to position and intensity could track

5775-587: Was causing echoes on their screens, masking potential enemy targets. Techniques were developed to filter them, but scientists began to study the phenomenon. Soon after the war, surplus radars were used to detect precipitation. Since then, weather radar has evolved and is used by national weather services, research departments in universities, and in television stations ' weather departments. Raw images are routinely processed by specialized software to make short term forecasts of future positions and intensities of rain, snow, hail, and other weather phenomena. Radar output

5852-496: Was displayed. Although many stations have upgraded to HD-compatible versions of First Warning, the on-screen graphic map and/or scroll in some cases, may be displayed in anamorphic widescreen if the system is not properly set to a 16:9 display, causing partial cropping of the graphic outside of the safe area on 4:3 television sets. Severe weather terminology (United States) The NWS provides weather forecasts, hazardous weather alerts, and other weather-related products for

5929-523: Was increased to get a three-dimensional view of the precipitation, so that horizontal cross-sections ( CAPPI ) and vertical cross-sections could be performed. Studies of the organization of thunderstorms were then possible for the Alberta Hail Project in Canada and National Severe Storms Laboratory (NSSL) in the US in particular. The NSSL, created in 1964, began experimentation on dual polarization signals and on Doppler effect uses. In May 1973,

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