Radar Resources / Radar Data / Data Inventory

NEXRAD Level-II (Base) Data

All NEXRAD Level-II Data are available through NCDC. Level II data are the three meteorological base data quantities: reflectivity, mean radial velocity, and spectrum width. Data are collected and recorded in units of files which typically contain 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 2432 byte base data and message records.

NEXRAD Level-III Products

Detailed List of Level-III Product Codes


There are a total of 41 Level-III products routinely available from NCDC. 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 & city background maps. The Radar Product Price Sheet has further information on hard copy radar products and pricing information. A Detailed List of Level-III Product Codes is also available.

A brief description and possible uses of these products are included below.


General Products

General products include the baseline reflectivity and velocity, and also algorithmic graphic products spectrum width, vertical integrated liquid, and VAD wind profile.
Base Reflectivity (NOR, N1R, N2R, N3R /19)
A display of echo intensity measured in dBZ. This product is used to detect precipitation, evaluate storm structure, locate boundaries and determine hail potential. The 4 lowest elevations angles are available.
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). Negative values are represented by cool colors (green) while positive values are represented by warm colors (red). This product is used to estimate wind speed and direction, locate boundaries, locate severe weather signatures and identify suspected areas of turbulence.
Storm Relative Velocity (NOS, N1S, N2S, N3S /56)
When the motion of storms are subtracted from the wind field, the result is a picture of the wind as if the storms were stationary. Color induces 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)
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.
Low/Mid/High Layer Composite Reflectivity (NLL/65, NML/66, NHL/90)
A display of maximum reflectivity for three different height ranges within the volume scan. This product is used to reveal the highest reflectivities in all echoes, examine storm structure features and determine intensity of storms.
Vertical Integrated Liquid (NVL/57)
The water content of a 2.2 X 2.2 nmi column of air which is color coded and plotted on a 124 nmi 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)
An image of the echo top heights color coded in user-defined increments. This product is used 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 1000 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)
A measurement 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)
A measurement related to the similarity between the behavior of the horizontally and vertically polarized pulses 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)
A measurement of difference between the horizontal and vertical pulses phase changes as they travel through the atmosphere. Interpreting Specific Differential Phase (KDP) can be very difficult. It's primary use involves detecting areas of heavy rain. KDP values are largest when going through areas dominated by large rain drops. 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)
Computer algorithm output that determines the most likely classification of the targets in the radar volume. The product displays which of the pre-defined categories most likely was 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)
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 hydrometeor classification obtained from the best/lowest available scan at each location. This product is used as input to the dual-polarization precipitation estimation products.

Precipitation Products

Precipitation products are estimated ground accumulated rainfall. Estimates are based off a reflectivity and rainfall rate relationship called Z-R. Learn more about Z-R here.
One Hour Precipitation (N1P/78)
A display of estimated one hour precipitation accumulation on a 1.1 nmi (Nautical Mile) 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.
Three Hour Precipitation (N3P/79)
Same as one hour, except for a three hour period.
Storm Total Precipitation (NTP/80)
The estimated storm total precipitation accumulation on a 1.1 nmi x 1 Degree grid continuously updated since the precipitation event began. This product uses the PPS algorithm and is used 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 LFM (4.7625 km HRAP) grid. This is a 8 bit product with 255 possible precip values. This product is used to assess 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 available on a 1.1 nmi 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 available on a .13 nmi 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 available on a 1.1 nmi 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 available on a .13 nmi 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. The differences are computed 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. The differences are computed 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 dualpolarization 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 are alphanumeric data that gives detailed information on certain parameters for an identified storm cell.
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 which 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.
Mesocyclone (NME/60)
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 which shows an intense gate to gate azimuthal shear associated with tornadic- scale rotation. It is depicted by a red triangle with numerical output of location and height.
Storm Tracking Information (NST/58)
A product which shows a plot of the past hours 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

Radar messages are sent by the radar site to users in order to know more about the radar status and special product data.
General Status Message (GSM/2)
A text message describing the status of the Radar site. A reason may be provided 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).