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Terminal Doppler Weather Radar

The Terminal Doppler Weather Radar (TDWR) network is a Doppler weather radar system operated by the Federal Aviation Administration (FAA). The system is primarily used to detect hazardous wind shear conditions, precipitation, and winds over and near major U.S. airports with frequent exposure to thunderstorms. As of 2014, there were 45 operational TDWR-Supplemental Project Generator (SPG) radar systems in major metropolitan locations across the United States and Puerto Rico. NCEI provides access to archived TDWR Level-II data and Level-III products.

Access Methods

NCEI provides access to TDWR Level-II data and Level-III products, precipitation, overlay, and radar messages. Digital data is available for free and paper copies can be purchased and certified. See Data Certification for more information on hard copy radar products, pricing, and certification information.

NEXRAD Inventory
A search and discovery hub for NEXRAD data that hosts a variety of data access tools, statistics, and documentation.
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Climate Data Online
Use Climate Data Online (CDO) to search for data by county, city, and zip code.
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Radar Map
The Interactive Radar Map Tool shows supplemental data in support of NCEI's Weather Radar Archive, and includes search parameters for time frame, station(s), and altitude.
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Parts of the NEXRAD archive inventory are available on a variety of cloud platforms  as part of the NOAA Big Data Project (BDP) efforts.
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The Weather and Climate Toolkit (WCT) provides data access and visualization web services for weather and climate data.
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The online store provides access to documentation, paper copies of data, and other related products.
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Note: There are occasional gaps and missing data for each site in the archive that are caused by scheduled maintenance at radar sites, unplanned downtime due to severe weather, communications problems, archival problems, and other issues related to maintenance and infrastructure. The data access pages include lists or visualizations of file availability that document these absences.

Data Types

Level-II (Base) Data

NCEI provides access to all TDWR Level-II data. Level-II data are grouped into three meteorological base quantities: reflectivity, mean radial velocity, and spectrum width. Data are stored in files that typically contain four, five, six, or ten minutes of base data. A data file consists of a 24-byte volume scan header record followed by numerous 2,432-byte base data and message records.

Level-III Products

NCEI provides access to 26 TDWR Level-III products. Most Level-III products are available as digital images, color or grayscale hard copy, and acetate overlay copies. Each copy includes state, county, and city background maps. See Data Certification for more information on hard copy radar products, pricing, and certification information.

Product Descriptions

General products include Base Reflectivity and Base Velocity as well as graphical products derived from algorithms including Spectrum Width, Vertically Integrated Liquid, and the Velocity Azimuth Display (VAD) Wind Profile.

Digital Base Reflectivity (TR0, TR1, TR2/181 or after 1/1/2020 TZ0, TZ1, TZ2/180)

A display of echo intensity measured in dBZ. These products are used to detect precipitation, evaluate storm structure, locate boundaries, and determine hail potential. The three lowest elevation angles are available with a maximum range of 48 nautical miles (nm).

Digital Base Velocity (TV0, TV1, TV2/182)

A measure of the radial component of the wind either toward (negative values) or away from (positive values) the radar. Cool colors (green) represent negative values and warm colors (red) represent positive values. These products are used to estimate wind speed and direction, locate boundaries, locate severe weather signatures, and identify suspected areas of turbulence. Data for the three lowest elevation angles are available, with a maximum range of 48 nm.

Long Range Digital Base Reflectivity (TZL/186)

Digital Reflectivity data are measured at an elevation angle of 0.6 degrees with a maximum range of 225 nm. When the FAA updated TDWR between January 2017 and May 2019, the elevation angle of this product became the same as the lowest elevation Reflectivity product (TR0 or TZ0).

Composite Reflectivity (NCR/37)

A display of maximum reflectivity for the total volume within the range of the radar. This product is used to reveal the highest reflectivities in all echoes, examine storm structure features, and determine intensity of storms.

Vertically Integrated Liquid (NVL/57)

The water content of a 2.2 x 2.2 nm column of air, which is color-coded and plotted on a 48-nm map. This product is used as an effective hail indicator, to locate most significant storms, and to identify areas of heavy rainfall.

Echo Tops (NET/41)

This product generates a color coded image that shows the height of an echo top. Scientists use this product to quickly estimate the most intense convection and higher echo tops, as an aid to identify storm structure features, and for pilot briefing purposes.

VAD Wind Profile (NVW/48)

A graphic display of wind barbs plotted on a height staff in 1,000-ft increments. The current (far right) and up to 10 previous plots may be displayed simultaneously. This product is an excellent tool for meteorologists in weather forecasting, severe weather, and aviation.

Precipitation products are estimated ground accumulated rainfall. Estimates are based on a reflectivity and rainfall rate relationship called Z-R.

One-Hour Precipitation (N1P/78)

A display of estimated one hour precipitation accumulation on a 1.1-nm x 1-degree grid using the Precipitation Processing System (PPS) algorithm. This product is used to assess rainfall intensities for flash flood warnings, urban flood statements, and special weather statements.

Storm Total Precipitation (NTP/80)

This product uses the PPS algorithm to create a continuously updated estimate of a storm’s accumulated precipitation. Accumulation is tracked on a 1.1 nm x 1 degree grid. Scientists use this product to locate flood potential over urban or rural areas, estimate total basin runoff, and provide rainfall data 24 hours a day.

Digital Precipitation Array (DPA/81)

An array format of estimated one-hour precipitation accumulations on the 1/4 Lyon-Fedder-Mobarry (LFM) or 4.7625 km Hydrographic Rainfall Analysis Project (HRAP) grid. This is an 8-bit product with 255 possible precipitation values. This product is used to assess rainfall intensities for flash flood warnings, urban flood statements, and special weather statements.

Overlay products provide detailed information for identified storm cells.

Storm Structure (NSS/62)

Overlay products provide detailed information for identified storm cells.

Hail Index (NHI/59)

A product designed to locate storms that have the potential to produce hail. Hail potential is labeled as either probable (hollow green triangle) or positive (filled green triangle). Probable means the storm is probably producing hail and positive means the storm is producing hail.

Digital Mesocyclone Detection Algorithm (NMD/141)

This product is designed to display information regarding the existence and nature of rotations associated with thunderstorms. Numerical output includes azimuth, range, and height of the mesocyclone.

Tornadic Vortex Signature (NTV/61)

A product that shows an intense gate-to-gate azimuthal shear associated with tornadic-scale rotation. It is depicted as a red triangle with numerical output of location and height.

Storm Tracking Information (NST/58)

A product that shows a plot of the past hour's movement, current location, and forecast movement for the next hour or less for each identified thunderstorm cell. This product is used to determine reliable storm movement.

Radar messages provide information about the radar status and special product data.

General Status Message (GSM/2)

A text alert that shares the radar site and transmission status

Free Text Message (FTM/5)

A text alert that describes upcoming, ongoing, or completed events at the radar site such as downtime or maintenance.

Radar Status Log (RSL/152)

A running daily log of status, errors, and messages from the Radar Product Generator (RPG) and Radar Data Acquisition (RDA) processing systems.

History

TDWR was developed in the early 1990s at the Massachusetts Institute of Technology (MIT) Lincoln Laboratory. The TDWR system was funded by the U.S. Federal Aviation Administration (FAA) to assist air traffic controllers by providing real-time wind shear detection and high-resolution precipitation data.

In 2004, the NWS established the policy with the FAA to allow the operational use of TDWR data and began to develop the SPG. Initial deployment of the SPG began in 2005 and finished in 2008. As of 2014, there were 45 operational TDWR-SPG radar systems in major metropolitan locations across the United States and Puerto Rico.

TDWR/WSR-88D Comparison

TDWR has a finer range resolution than the Weather Surveillance Radar, 1988 Doppler (WSR-88D), or any other FAA radar with weather channel capability. The TDWR utilizes a range gate resolution of 150 m for Doppler data. It has a resolution of 150 m for reflectivity data within 135 km and 300 m from beyond 135 km to 460 km. However, data processing by the NWS SPG system converts the Long Range Reflectivity data (Level- II data and TZL product) to 300 m. By contrast, the WSR-88D employed by the National Weather Service, FAA, and Department of Defense has a maximum range gate resolution of 250 m for Doppler and 1 km for surveillance data. 

TDWR angular (azimuth) resolution is nearly double that of the WSR-88D. Each radial in TDWR has a beam width of 0.55 degrees. However, the TDWR samples radials every 1.0 degree, thus the effective angular resolution is 0.55 degrees vertically by 1.0 degree azimuthally. The average beam width for the WSR-88D is 0.95 degrees. 

Specifications Comparison

 WSR-88DTDWR
Wavelength10 cm5 cm
Volume Scan Time4 minutes in VCP 126 minutes, and 1 min at lowest elevation HAZ
Beam Width1.25 degrees0.5 degrees
Range Gate0.13 nm in velocity
0.54 nm in reflectivity
0.067 nm
Max Unambiguous VelocityUp to 62 kts20-30 kts
Max Doppler Range230 km90 km

Technical Information

How Does the Radar Collect Data?

TDWR was designed to look for low-altitude phenomena such as wind shifts over the runways, wind shear along the immediate approach and departure corridors, and downbursts. These radars are located close to major airports with the scanning strategy optimized to sample the atmosphere over its associated airport. The system employs a scanning strategy called monitor mode, which is similar to the WSR-88D clear-air mode. TDWR remains in monitor mode until one of the two following conditions are recognized:

  1. A region of 20 dBZ echoes located within 24.3 nautical miles (nm) from the associated airport with a nominal areal extent of 1.3 nm and an altitude of at least 1.3 nm above ground level or
  2. The radar detects wind shear or a microburst.

This is a departure from WSR-88D operations that can switch from clear-air mode to precipitation mode if the aerial coverage of precipitation exceeds an adaptable parameter anywhere on the scope. The TDWR ties its decision on the area of influence directly to its associated airport.

Volume Coverage Pattern (VCP) 90

VCP 90 is the TDWR monitor mode (clear air) and consists of 16 scans in about six minutes. The first cut is always a low pulse repetition frequency (PRF), long-range scan (276 km). All remaining scans are short range (90 km). There is a small variation in the elevation angles of the lower scans, but all scans above 5 degrees are the same in all systems. 

Volume Coverage Pattern (VCP) 80

VCP 80 is the TDWR hazardous mode (precipitation mode). The first cut is always a low PRF, long-range scan (276 km). There are two sub-volumes or aloft scans contained in each full volume as denoted by the use of red and orange. Every fourth scan, the TDWR provides a short-range elevation scan at the same elevation as cut two.