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NEXRAD Products

NCEI provides descriptions and possible uses of the following radar products: Next Generation Weather Radar (NEXRAD) Level-II, NEXRAD Level-III, Precipitation, Overlay, Radar Messages, and Products. All data are available digitally at NCEI at no charge and paper copies are available for purchase. Certification of paper data is also available.

NEXRAD Level-II (Base) Data

All NEXRAD Level-II data are available through NCEI. Level-II data are the three meteorological base data quantities: reflectivity, mean radial velocity, and spectrum width. Data collection and recording are in unit of files, which 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

There are over 75 Level-III products routinely available from NCEI. Most Level-III products are available as digital images, color hard copy, gray scale hard copy, or acetate overlay copies. Each copy will include state, county, and city background maps. The Certification of Data page has further information on hard copy radar products, pricing, and certification information. A Detailed List of Level-III Product Codes is also available.

Brief descriptions and possible uses of these products are included below.

General Products

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.
  • Base Reflectivity (NOR, NAR, N1R, NBR, N2R, N3R/19)
    A display of echo intensity measured in dBZ. Scientists use these products to detect precipitation, evaluate storm structure, locate boundaries, and determine hail potential. Four or six of the lowest elevations angles are available, depending on the scanning mode of the Radar. Sixteen possible data levels are also available.
  • Digital Base Reflectivity (NOQ, NAQ, N1Q, NBQ, N2Q, N3Q/94)
    The same as N*R products defined above except data values are actual reflectivity values instead of categories.
  • Base Velocity (NOW/25, NOV, 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 (NOU, NAU, N1U, NBU, N2U, N3U/99)
    The same as N*V products defined above except data values are actual velocity values instead of categories.
  • Storm Relative Velocity (NOS, N1S, N2S, N3S/56)
    When the motion of storms is subtracted from the wind field, the result is a picture of the wind as if the storms were stationary. 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. The primary use of this product is to estimate turbulence associated with mesocyclones and boundaries.
  • Composite Reflectivity (NCO/36, NCR/37, NCZ/38)
    Composite Reflectivity is a display of maximum reflectivity for the total volume within the range of the radar. 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)
    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.
  • Vertically Integrated Liquid (NVL/57)
    The water content of a 2.2 x 2.2 nautical mile (nm) column of air, which is color-coded and plotted on a 124-nm map. This product is an effective hail indicator, used to locate most significant storms, and to identify areas of heavy rainfall.
  • Echo Tops (NET/41)
    An image of the echo top heights color-coded in user-defined increments. Scientists use this product for a quick estimation of the most intense convection and higher echo tops, as an aid in identification of 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 500-ft. or 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) (N0X, N1X, N2X, N3X/159) (Dual-Pol. only)
    Differential Reflectivity values are measurements related to the returned energy difference between the vertical and horizontal radar pulses. Large positive values indicate that targets are generally much larger horizontally than vertically. Values near zero indicate the targets are generally spherical. Negative values indicate targets are larger in the vertical than in the horizontal. The four lowest elevation angles are available.
  • Correlation Coefficient (CC) (N0C, N1C, 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 are behaving 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). The four lowest elevation angles are available.
  • Specific Differential Phase (KDP) (N0K, N1K, N2K, N3K/163) (Dual-Pol. only)
    Specific Differential Phase is a measurement of difference between the horizontal and vertical pulse phase changes as they travel through the atmosphere. Interpreting Specific Differential Phase (KDP) can be very difficult. Its primary use involves detecting areas of heavy rain. KDP values are largest when going through areas dominated by large raindrops. In some cases, regions with high KDP values may also contain melting hail. The four lowest elevation angles are available.
  • Hydrometeor Classification (HC) (N0H, N1H, N2H, N3H/165 (Dual-Pol. only)
    Hydrometeor Classification is a computer algorithm output that determines the most likely classification of the targets in the radar volume. The product displays the predefined categories that were most likely the cause of the radar echo at that location. The four lowest elevation angles are available.
  • Melting Layer (ML) (N0M, N1M, N2M, N3M/166) (Dual-Pol. only)
    Melting Layer is a computer algorithm output that determines where the radar beam intersects the level of the atmosphere where frozen precipitation starts melting. This product provides users with information on whether precipitation should generally be frozen, melting, or liquid in a particular area. This product is generated on 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 freezing level data entered manually or from computer models.
  • 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.

Precipitation Products

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 assesses rainfall intensities for flash flood warnings, urban flood statements, and special weather statements.
  • Three-Hour Precipitation (N3P/79)
    A display of 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)
    The estimated storm total precipitation accumulation on a 1.1-nm x 1-degree grid continuously updated since the precipitation event began. This product uses the PPS algorithm. 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 1/4 LFM (4.7625 km 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 will have any bias applied. This product will be 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 will have any bias applied. The product shall be a volume-based product and shall be updated every volume scan. However, this product will only contain a graphical image whenever one of the systems (legacy PPS or dual-polarization QPE) has detected precipitation and is accumulating storm total information. That is, this product will only have a graphical image present when at least one of the systems is generating storm total products.
  • Digital Precipitation Rate (DPR/176) (Dual-Pol. only)
    This product displays the instantaneous precipitation rate using the dual-polarization QPE algorithm.

Overlay Products

Overlay products provide detailed information for identified storm cells.
  • Storm Structure (NSS/62)
    A table displaying information on storm attributes, which include 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)
    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 by 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.

Radar Messages

Radar messages provide information about the radar status and special product data.
  • General Status Message (GSM/2)
    The General Status Message is a text message describing the status of the radar site. The message may provide a reason if the radar is not transmitting.
  • 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).