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NEXRAD or Nexrad (Next-Generation Radar) is a network of 158 high-resolution Doppler radars operated by the National Weather Service, an agency of the National Oceanic and Atmospheric Administration (NOAA) within the United States Department of Commerce. Its technical name is WSR-88D, which stands for Weather Surveillance Radar, 1988, Doppler. NEXRAD detects precipitation and atmospheric movement or wind. It returns data which when processed can be displayed in a mosaic map which shows patterns of precipitation and its movement. The radar system operates in two basic modes, selectable by the operator: a slow-scanning clear-air mode for analyzing air movements when there is little or no activity in the area, and a precipitation mode with a faster scan time for tracking active weather. NEXRAD has an increased emphasis on automation, including the use of algorithms and automated volume scans.

Contents 1 Deployment 2 Scan strategies 3 Future enhancements 4 Applications 5 Bibliography 6 In Popular Culture 7 See also 8 References 9 External links

After more than 30 years of research on operational Doppler radar systems, the National Weather Service (NWS) began to deploy the WSR-88D in 1988. It replaced WSR-74 and even WSR-57 units from 1974 and 1957 respectively. The first installation was completed in the Fall of 1990 in Norman, Oklahoma, however, the first installation of a WSR-88D for use in everyday forecasts was in Sterling, Virginia on June 12, 1992. The last system was installed in North Webster, Indiana on August 30, 1997. The site locations were strategically chosen to provide the most overlapping coverage between radars in case one failed during a severe weather event. Where possible, they were co-located with NWS Weather Forecast Offices to permit quicker access to maintenance technicians.^[1]

Initial development of the NEXRAD system started in 1982 at the National Severe Storms Laboratory in Norman, Oklahoma. Members of the early NEXRAD team included Timothy O'Bannon, a meteorologist and hydrologist who, as an amateur ornithologist also recognized the radar's additional capabilities for tracking bird migration patterns. (O'Bannon, Tim 1995. Anomalous WSR-88D Wind Profiles - Migrating Birds? American Meteorological Society 27th Conference on Radar Meteorology Preprints: 663-665).

Unlike its predecessors, the WSR-88D antenna is not directly controllable by the user. Instead, the radar system continually refreshes its three-dimensional database via one of several predetermined scan patterns. Since the system samples the atmosphere in three-dimensions, there are many variables that can be changed depending on the desired output. There are currently six Volume Coverage Patterns (VCP) available to NWS meteorologists. Each VCP is a predefined set of instructions given to the antenna that control the rotation speed, transmit/receive mode, and elevation angles. They use a specific numbering scheme:

• Clear Air: VCP 31 and 32 (two digits beginning with 3)
• Shallow Precipitation: VCP 21 (two digits beginning with 2)
• Convection: VCP 11 and 12 (two digits beginning with 1)
• Multiple Pulse Frequency Dealiasing: VCP 121 (three digits beginning with a 1, followed by the 2 digit number of VCP with similar elevation angles)

VCP	Scan Time (min)	Elevation angles (°)	Usage	Special attributes
11	5	0.5, 1.5, 2.4, 3.4, 4.3, 5.3, 6.2, 7.5, 8.7, 10, 12, 14, 16.7, 19.5	Convection, especially when close to the radar	Has the best overall volume coverage.
12	4	0.5, 0.9, 1.3, 1.8, 2.4, 3.1, 4.0, 5.1, 6.4, 8.0, 10.0, 12.5, 15.6, 19.5	Convection, especially activity at longer ranges	Focuses on lower elevations to better sample the lower levels of storms.
121	5.5	0.5, 1.5, 2.4, 3.4, 4.3, 6.0, 9.9, 14.6, 19.5	Large number of rotating storms, tropical systems, or when better velocity data is needed.	Scans lower cuts multiple times with varying pulse repetitions to greatly enhance velocity data.
21	6	0.5, 1.5, 2.4, 3.4, 4.3, 6.0, 9.9, 14.6, 19.5	Shallow precipitation	Rarely used for convection due to sparse elevation data and long completion time.
31	10	0.5, 1.5, 2.5, 3.5, 4.5	Detecting subtle boundaries or wintry precipitation	Long-pulse
32	10	0.5, 1.5, 2.5, 3.5, 4.5	Slow rotation speed allows for increased sensitivity. Default clear-air mode, reduces wear on antenna.	Short-pulse

Currently, a large hardware upgrade to the Radar Data Acquisition (RDA) units is underway. The original hardware and software at the radar sites had very limited expandability. To enable more efficient future enhancements to radar products, an "Open RDA" is being installed at all WSR-88D sites nationwide. In addition to large increases in computing power, the new software architecture allows for easier installation of upgrades, including the latest algorithms. This will pave the way for numerous planned improvements over the next decade.

The next major upgrade is likely to be polarimetric radar, which adds vertical polarization to the current horizontal radar waves, in order to more accurately discern what is reflecting the signal. This so-called dual polarization allows the radar to distinguish between rain, hail and snow, something the horizontally polarized radars cannot accurately do. Early trials have shown that rain, sleet, snow, hail, birds, insects, and ground clutter all have different signatures with dual-polarization, which could mark a significant improvement in forecasting winter storms and severe thunderstorms. [1]

Beyond dual-polarization, the advent of phased array radar will probably be the next giant leap in severe weather detection. Its ability to rapidly scan large areas would give an enormous advantage to radar meteorologists. Any large-scale installation by the NWS is unlikely to occur before 2010. Such a system would more likely be installed separate from the existing WSR-88D network, perhaps only in areas like the Great Plains where tornadoes are more common.

One practical application under experiment is using the mosaic map to suggest alternate flight paths for the airliners to avoid turbulence.^[2]

• David Atlas, Radar in Meteorology: Battan Memorial and 40th Anniversary Radar Meteorology Conference, published by the American Meteorological Society, Boston, 1990, 806 pages, ISBN 0-933876-86-6, AMS Code RADMET.

In the movie Twister, references are made about NEXRAD, in the form of mobile computing systems used by storm chasers containing "NEXRAD realtime"

• LLWSAS
• Microburst
• Weather radar

v • d • e Meteorological instrumentation and equipment (Earth based)

Anemometer | Barograph | Barometer | Ceiling balloon | Ceiling projector | Ceilometer | Dark adaptor goggles | Disdrometer | Field mill | Hygrometer | Ice Accretion Indicator | LIDAR | Lightning detector | Nephelometer | Nephoscope | Pyranometer | Radiosonde | Rain gauge | Snow gauge | SODAR | Solarimeter | Sounding rocket | Stevenson screen | Sunshine recorders | Thermograph | Thermometer | Weather balloon | Weather radar | Weather vane | Windsock | Wind profiler

v • d • e Meteorological Observation Systems and Weather Stations (Earth based)

Argo | Global Atmosphere Watch | Aircraft Communication Addressing and Reporting System (ACARS) | Aircraft Meteorological Data Relay (AMDAR) | Aircraft report (AIREP} | Automatic weather station | Automated airport weather station | Coastal-Marine Automated Network (C-MAN) | Global Sea Level Observing System | Meteorological Aerodrome Report (METAR) | NEXRAD radar | Pilot report (PIREP) | Remote Automated Weather Stations (RAWS) | SST buoys | TAMDAR | Tide gauges | Weather buoys | Hurricane Hunters | Dropsonde | Weather balloon | Weather ship

v • d • e US Weather radars
Military weather radars	AN/APQ-13 · AN/APS-2F · AN/CPS-9 · AN/FPS-41 · AN/FPS-77
Weather Surveillance Radars	WSR-1 and -1A · WSR-3 · WSR-4 · WSR-57 · WSR-74C and -74S  · WSR100-S · WSR-88D (NEXRAD)
Research radars	ADRAD · ARMOR · Cimarron · CORAD · CSU-CHILL · CSU-Pawnee · DOW · KPOL · NOAA/ETL · NOAA Ron Brown's Doppler  · NPOL · NSSL 10 cm Doppler  · PAR at NSSL  · SKYWATER · SMART-R · TOGA · UND

1. ^ WSR-88D Radar, Tornado Warnings and Tornado Casualties.
2. ^ Airline flights get less turbulent - EE Times, Sep 11, 2007

• http://www.weather.gov
• http://weather.noaa.gov/radar/national.html
• http://www.srh.noaa.gov/srh/sod/radar/radinfo/radinfo.html
• http://www.srh.noaa.gov/srh/sod/radar/radinfo/about.html
• http://www.nssl.noaa.gov/researchitems/radar.shtml
• http://www.wunderground.com/radar/help.asp
• http://weatheratmyhouse.com
• NEXRAD Weather Links