The Next Generation Weather Radar (NEXRAD) system is a network of 160 high-resolution S-band Doppler weather radars jointly operated by the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the U.S. Air Force. The NEXRAD system detects precipitation and wind, and its data can be processed to map precipitation patterns and movement. NCEI provides access to archived NEXRAD Level-II data and Level-III products.
Access Methods
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 data can be accessed through the following data access services:
NEXRAD Inventory
A search and discovery hub for NEXRAD data that hosts a variety of data access tools, statistics, and documentation.
Climate Data Online
Use Climate Data Online (CDO) Search for data by county, city, and zip code.
Interactive 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.
NOAA Open Data Dissemination
NCEI releases the NOAA NEXRAD archive inventory as a reference for users in support of the NOAA Open Data Dissemination (NODD) efforts.
Weather and Climate Toolkit
The NCEI Weather and Climate Toolkit (WCT) provides data access and visualization web services weather and climate data.
NCEI Online Store
The online store provides access documentation, paper copies of data, and other related products.
Data Types
Level-I Event Data
This dataset contains the Level-I (L1) raw radar event data recorded at Next Generation Radar (NEXRAD) sites and collected by the NOAA National Weather Service (NWS) Radar Operations Center (ROC) for specific radar case studies. It includes only the Level 1 data that has been used for algorithm development and verification by the ROC and its partners. NEXRAD operational sites and test sites are used. The period of record is from 2008 to present with additional data years planned. The number of case studies per year ranges from 1 to 33, with an average of approximately 10 per year. The data files are in the native compressed file format as Time Series (TS) Archive. The data files have been aggregated by event and by hour for the archive with a total data volume of approximately 20 TB. An event summary file with descriptive information is included for each case study. An inventory of events is available here [add link].
This dataset is not currently available for direct download from NCEI, but is available by request from the offline archive.
NEXRAD Level-II (Base) Data
Level-II (L2) data are grouped into three meteorological base quantities: reflectivity, mean radial velocity, and spectrum width. Additional categories include dual-polarization base data of differential reflectivity, correlation coefficient, and differential phase. Data are stored in files that typically contain four, five, six, or ten minutes of base data depending on the volume coverage pattern. A data file consists of a 24-byte volume scan header record followed by numerous 2,432-byte base data and message records.
NEXRAD Level-III Products
Over 75 Level-III (L3) products are routinely available from NCEI. Most L3 products are available as digital images, color hard copy, grayscale hard copy, or acetate overlay copy. Each copy includes state, county, and city background maps.
Product Descriptions
Base Reflectivity (N0R, N1R, N2R, N3R/19 and N0Z/20)
A display of echo intensity measured in decibels relative to Z (dBZ). Scientists use these products to detect precipitation, evaluate storm structure, locate boundaries, and determine hail potential. Four low elevation angles are available, with specific elevation angles depending on the scanning mode of the Radar. Sixteen possible data levels are also available.
Digital Base Reflectivity (NXQ, NYQ, NZQ, N0Q, NAQ, N1Q, NBQ, N2Q, N3Q/94)
The same as N*R products defined above, except data values are actual reflectivity values instead of categories, data extends to further range, and additional elevations are available. Products from elevation angles at or below 3.5 degrees are available, and select sites may also scan at an additional low elevation angle, as low as -0.2 degrees. Specific elevation angles depend on the site and scanning mode of the Radar.
Base Velocity (N0W/25, N0V, N1V, N2V, N3V/27)
A measure of the radial component of the wind either toward the radar (negative values) or away from the radar (positive values). Cool colors (green) represent negative values and warm colors (red) represent positive values. Scientists use these products to estimate wind speed and direction, locate boundaries, locate severe weather signatures, and identify suspected areas of turbulence.
Digital Base Velocity (NXU, NYU, NZU, N0U, NAU, N1U, NBU, N2U, N3U/99)
The same as N*V products defined above, except data values are actual velocity values instead of categories, data extends to further range, and additional elevations are available.
Storm Relative Velocity (N0S, N1S, N2S, N3S/56)
A stationary storm image that is generated by removing storm motion measurements from the wind field. Color indices are the same as base velocity. Comparing the storm relative motion image with base velocity image helps identify the rotating storm.
Base Spectrum Width (NSP/28, NSW/30)
A measure of velocity dispersion within the radar sample volume. This product's primary use is to estimate turbulence associated with mesocyclones and boundaries.
Composite Reflectivity (NCO/36, NCR/37, NCZ/38)
Composite Reflectivity displays the maximum reflectivity from all scanned heights above the ground during the volume scan. These products reveal the highest reflectivities in all echoes, examine storm structure features, and determine the intensity of storms.
Low/Mid/High Layer Composite Reflectivity (NLL/65, NML/66, NHL/90, NLA/67)
Low/Mid/High Layer Composite Reflectivity is a display of maximum reflectivity for three different height ranges within the volume scan. Use this product to reveal the highest reflectivities in all echoes, examine storm structure features, and determine the intensity of storms. The NLA/67 product is similar to NLL/65, but edited to remove contamination from anomalous propagation.
Vertically Integrated Liquid (NVL/57, DVL/134)
This product color codes and plots the water content of a 2.2 x 2.2 nautical mile (nm) column of air. It is an effective hail indicator that can be used to locate most significant storms and identify areas of heavy rainfall. The DVL version of the product provides a higher spatial resolution and enhanced processing.
Echo Tops (NET/41, EET/135)
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. The EET version of the product provided a higher spatial resolution, and enhanced processing, including identification of weather that is higher than the radar can scan.
VAD Wind Profile (NVW/48)
This product plots wind barbs 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.
Differential Reflectivity (ZDR) (NXX, NYX, NZX, N0X, NAX, N1X, NBX, N2X, N3X/159) (Dual-Pol. only)
Differential Reflectivity values are measurements related to the returned energy difference between the vertically and horizontally polarized radar pulses. Large positive values indicate wider targets. Values near zero indicate the targets are generally spherical. Negative values indicate targets are larger in the vertical than in the horizontal. Products from elevation angles at or below 3.5 degrees are available, and select sites may also scan at an additional low elevation angle, as low as -0.2 degrees.
Correlation Coefficient (CC) (NXC, NYC, NZC, N0C, NAC, N1C, NBC, N2C, N3C/161) (Dual-Pol. only)
Correlation Coefficient values are measurements related to the similarity between the behaviors of the horizontally and vertically polarized pulses and how they behave within a pulse volume. Values between 0.95 and 1.0 indicate near uniformity in pulse behavior. Meteorological targets with complex shapes, or with a large degree of variety, will generally have values between 0.85 and 0.95. Biological targets, anthropogenic targets, and ground clutter tend to cause very different behaviors between the pulses, resulting in values less than 0.9 (and often less than 0.7).
Specific Differential Phase (KDP) (NXK, NYK, NZK, N0K, NAK, N1K, NAB, N2K, N3K/163) (Dual-Pol. only)
Specific Differential Phase measures the difference between the horizontally and vertically polarized pulse phase changes as they travel through the atmosphere. KDP can be used to detect areas of heavy rain, and high KDP values correlate with large raindrops (and in some cases, melting hail).
Hydrometeor Classification (HC) (NXH, NYH, NZH, N0H, NAH, N1H, NBH, N2H, N3H/165 (Dual-Pol. only)
Hydrometeor Classification is a computer algorithm output that tries to classify targets in the radar volume. The product compares targets to a set of predefined categories, and displays a list of the most likely echo sources.
Melting Layer (ML) (NXM, NYM, NZM, N0M, NAM, N1M, NBM, N2M, N3M/166) (Dual-Pol. only)
Melting Layer is a computer algorithm output that determines the atmospheric melting point for frozen precipitation. This product provides information about the state (frozen, melting, or fully liquid) of precipitation at different altitudes in a particular area. This product is generated for each elevation angle that the radar scans and can be particularly useful for tracking icing conditions above the surface. It may have problems when surface temperatures are below freezing, in mountainous locations, or when data needed for the algorithm is limited. When radar echoes are insufficient for the algorithm to work properly, it will default to the manually entered or model generated freezing level data.
Hybrid Hydrometeor Classification (HHC/177) (Dual-Pol. only)
The Hybrid Hydrometeor Classification is obtained from the best/lowest available scan at each location. This product serves as input to the dual-polarization precipitation estimation products.
One-Hour Precipitation (N1P/78)
This product displays estimated one-hour precipitation accumulation on a 1.1-nm x 1-degree grid using the Precipitation Processing System (PPS) algorithm. This product assesses rainfall intensities for flash flood warnings, urban flood statements, and special weather statements.
Three-Hour Precipitation (N3P/79)
N3p/79 charts estimated three-hour precipitation accumulation on a 1.1-nm x 1-degree grid using the Precipitation Processing System (PPS) algorithm. This product assesses 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)
The Digital Precipitation Array is a format of estimated one-hour precipitation accumulations on the 1/4Lyon-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 assesses rainfall intensities for flash flood warnings, urban flood statements, and special weather statements.
One-Hour Precipitation (OHA/169) (Dual-Pol. only)
One-hour precipitation accumulation is available on a 1.1-nm x 1-degree grid. The Quantitative Precipitation Estimate (QPE) dual-polarization precipitation algorithm is used and 16 possible data levels are available.
One-Hour Precipitation (DAA/170) (Dual-Pol. only)
One-hour precipitation accumulation is available on a 0.13-nm x 1-degree grid. The dual-polarization QPE algorithm is used and 256 possible data levels are available.
Storm Total Precipitation (PTA/171) (Dual-Pol. only)
Storm total precipitation accumulation is available on a 1.1-nm x 1-degree grid. The dual-polarization QPE algorithm is used and 16 possible data levels are available.
Storm Total Precipitation (DTA/172) (Dual-Pol. only)
Storm Total precipitation accumulation is available on a .13 nm x 1 degree grid. The dual-polarization QPE algorithm is used and 256 possible data levels are available.
One-Hour Precipitation Difference (DOD/174) (Dual-Pol. only)
The difference in hourly precipitation estimates between the PPS (Non-Dual-Pol.) algorithm and the QPE (Dual-Pol.) algorithm. Scientists compute the differences by subtracting the latest one-hour estimate computed by the legacy PPS from the one-hour estimates computed by the QPE. Neither estimate has any bias applied. This product is generated every volume scan whether or not precipitation has been detected.
Storm Total Precipitation Difference (DSD/175) (Dual-Pol. only)
The difference in storm total precipitation estimates between the PPS (Non-Dual-Pol.) algorithm and the QPE (Dual-Pol.) algorithm. Scientists compute the differences by subtracting the storm total estimates computed by the legacy PPS from the storm total estimates computed by the QPE. Neither estimate has any bias applied. The product is volume-based and is updated every volume scan. However, it only generates a graphic when one of the systems (legacy PPS or dual-polarization QPE) detects precipitation and accumulates storm total information.
Digital Precipitation Rate (DPR/176) (Dual-Pol. only)
This product displays the instantaneous precipitation rate using the dual-polarization QPE algorithm.
Storm Structure (NSS/62)
A table of storm attributes, including maximum reflectivity, maximum velocity at lowest elevation angle, storm overhang, mass weighted storm volume, storm area base and top, storm position, and storm tilt.
Hail Index (NHI/59)
A product designed to locate storms that have the potential to produce hail. Scientists label hail potential 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.
Mesocyclone (NME/60, NMD/141)
This product displays 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 which shows an intense gate-to-gate azimuthal shear, associated with tornadic- scale rotation. It depicts the tornadic vortex signature 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 hours movement, current location, and forecast movement for the next hour or less for each identified thunderstorm cell. Scientists use this product to determine reliable storm movement.
General Status Message (GSM/2)
A text alert that shares the radar site and transmission status.
Radar Coded Message (RCM/74)
A three-part message containing a tabular listing of composite reflectivity data, a vertical wind profile derived from the VAD algorithm, and the locations of algorithm-produced severe weather features such as the Hail Index (HI) and the Tornado Vortex Signature (TVS).
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
The National Weather Service (NWS) used World War II technology to develop and operate the Weather Surveillance Radars–1957 (WSR-57) network. This was followed by Weather Surveillance Radars–1974 (WSR-74) and then Weather Surveillance Radars–1988 Doppler (WSR-88D) or NEXRAD. The NEXRAD system is a joint effort of the U.S. Departments of Commerce, Defense, and Transportation. The controlling agencies are the NWS, Air Force Weather Agency, and Federal Aviation Administration (FAA).
In 1988, the NEXRAD agencies established the WSR-88D NOAA Radar Operations Center (ROC) in Norman, Oklahoma. The ROC provides centralized meteorological, software, maintenance, and engineering support for all WSR-88D systems. These systems are modified and enhanced during their operational life to meet changing requirements, technology advances, and improved understanding of the application of these systems to real-time weather operations. The ROC also operates test systems for hardware development and software upgrades to enhance maintenance, operation, and provide new functionality.
How Does Radar Collect Data?
The WSR-88D is made up of two functional components: Radar Data Acquisition (RDA) and the Radar Product Generator (RPG). RPG products are widely distributed and displayed on various radar product visualization systems. To adequately sample the atmosphere, the WSR-88D employs nine scanning strategies or Volume Coverage Patterns (VCPs). A VCP is a series of 360-degree sweeps of the antenna at predetermined elevation angles completed in a specified period of time. Other scan strategies are currently under development for the future.
Volume Coverage Patterns 11 and 21 (removed in 2018, with WSR-88D Build 18.0)
The Precipitation Mode uses these VCPs to better sample the vertical structure of convective weather echoes and improve temporal resolution. VCP 11 provides better vertical sampling of weather echoes than VCP 21 and is usually preferred in situations where convective precipitation is within 60 nautical miles (nmi) of the antenna. The VCP 11 has 14 elevation angles and completes 16 azimuthal scans in five minutes, while VCP 21 has nine elevation angles and completes 11 azimuthal scans in six minutes.
Volume Coverage Pattern 12
This VCP has the same number of elevation angles as VCP 11. However, denser vertical sampling at lower elevation angles provides better vertical definition of storms, improves the detection capability of radars impacted by terrain blockage for better rainfall and snowfall estimates, results in the identification of more storms, and provides quicker updates. This VCP has 14 elevation angles and completes 17 azimuthal scans in about 4.5 minutes.
Volume Coverage Patterns 31 and 32
The Clear-Air Mode, which optimizes the sensitivity of the WSR-88D, uses both of these VCPs. The VCP 31 (long pulse) provides a better signal-to-noise ratio, permitting lower reflectivity returns to be detected, while VCP 32 (short pulse) provides a higher unambiguous velocity. Both VCPs have five elevation angles, seven azimuthal scans, and take 10 minutes to complete.
Volume Coverage Pattern 121 (removed in 2020, with WSR-88D Build 19.0)
This VCP implements the multi-pulse repetition frequency detection algorithm (MPDA), which helps mitigate range/velocity aliasing (the Doppler Dilemma). This VCP has the same elevation angles (nine) as VCP 21, but completes 20 azimuthal scans in five minutes.
Volume Coverage Patterns 211, 212, and 221 (211 and 221 removed in 2018)
These VCPs have the same elevation angles as VCPs 11, 12, and 21 respectively. The "split cuts" (generally elevation angles below 1.5° except for VCP 31, which has a split cut at 2.5°) apply these VCPs, which implement the Sachidananda-Zrnic Algorithm. See chapter five, Part C, of the Federal Meteorological Handbook No.11 for additional information on split cuts. The Sachidananda-Zrnic Algorithm reduces range ambiguity for Doppler data.
Volume Coverage Pattern 215 (New in 2018, with WSR-88D Build 18.0)
This VCP scans the same elevation angles as VCP 12 and 212 below 10 degrees, the same angles as VCP 11 above 10 degrees, and like VCP 212 it employs the Sachidananda-Zrnic Algorithm as VCP 212 on the lowest elevations. It provides good vertical definition of storms at longer range and also when convective precipitation is within 60 nautical miles (nmi) of the antenna, and it reduces range ambiguity for Doppler data. VCP 215 scans 15 elevation angles in 6 minutes.
Volume Coverage Patterns 35 (New in 2018, with WSR-88D Build 18.0)
This Clear-Air Mode VCP provides improved sensitivity by scanning slowly to increase signal-to-noise ratio, permitting lower reflectivity returns to be detected. Like VCP 32, it uses the short pulse to provide a higher unambiguous velocity, it scans the same elevation angles as VCP 12 up through 6.4 degrees, and like VCP 212 it employs the Sachidananda-Zrnic Algorithm as VCP 212. It scans nine elevation angles in about 5.5 minutes.
Volume Coverage Pattern 112 (New in 2020, with WSR-88D Build 19.0)
This VCP implements the multi-pulse repetition frequency detection algorithm (MPDA), which helps mitigate range/velocity aliasing (the Doppler Dilemma). This VCP has the same elevation angles (14) as VCP 12, but completes 20 azimuthal scans in under eight minutes. It also employs the Sachidananda-Zrnic Algorithm on the lowest elevation angles.
Volume Coverage Pattern Supplemental Features
Many of these VCPs may also include scanning features such as AVSET, Base Tilt, and SAILS or MRLE. Automated Volume Scan Evaluation and Termination (AVSET) concludes a VCP at angles 6.2 degrees or above based on weather coverage at high elevations. Base Tilt adds an additional elevation scan lower than 0.5 degrees at select radar sites. Supplemental Adaptive Intra-Volume Low-Level Scan (SAILS) repeats the lowest elevation angle up to 3 times during a VCP, while Mid-Volume Rescan of Low-Level Elevations (MRLE) repeats up to the lowest 4 elevation angles during a VCP.
Resources
NEXRAD system details are available in Federal Meteorological Handbook No. 11, and the Office of the Federal Coordinator for Meteorology has additional publications available for download.
FMH-11 Volumes
- A - System Concepts, Responsibilities, and Procedures
- B - Doppler Radar Theory and Meteorology
- C - Products and Algorithms
- D - Unit Description and Operational Analysis
The official Interface Control Documents (ICDs) contain detailed information on the binary data formats and product specifications.
