Full Resolution Radar Loop
Fidelia Boldul
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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.
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:
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].
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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 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 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 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 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 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.
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.
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.
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 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.
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.
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.
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