NEXRAD Level III Data Products ----------------------------------------------------------------------------------- Info ----------------------------------------------------------------------------------- The National Weather Service (NWS) Doppler (NEXRAD) radar system estimates the intensity, position, velocity, and type of moisture in the atmosphere. Each radar site includes equipment and software that searches this basic precipitation data for patterns that estimate the presence (or likelyhood thereof) of various kinds of severe weather events. The datasets derived from this processing are called "NEXRAD Level III" products. SWDI currently provides access to the following 5 such products: 1) Hail Index Overlay (HI) - A product designed to locate storms which have the potential to produce hail. 2) Mesocyclone Overlay (M) - This legacy 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. 3) Storm Structure (SS) - A product designed to display 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. 4) Tornadic Vortex Signature Overlay (TVS) - A product which shows an intense gate to gate azimuthal shear associated with tornadic-scale rotation. 5) Digital Mesocyclone Detection Algorithm (MD) - This product is the sucessor to the legacy Mesocyclone (M) product and 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. ----------------------------------------------------------------------------------- Column Definitions and Units ----------------------------------------------------------------------------------- NEXRAD Level-III Hail 'nx3hail' Dataset: WSR_ID - "NEXRAD or TDWR SITE ID" CELL_ID - "CELL ID UNIQUE TO RADAR SITE" PROB - "PROBABILITY OF HAIL [PERCENT]" SEVPROB - "PROB. OF SEVERE HAIL [PERCENT]" MAXSIZE - "MAX SIZE [IN]" NEXRAD Level-III Legacy Mesocyclone 'nx3meso' Dataset: WSR_ID - "NEXRAD or TDWR SITE ID" CELL_ID - "CELL ID UNIQUE TO RADAR SITE" CELL_TYPE - "'MESO', '3DC SHR' or 'UNC SHR' RANGE - "RANGE [NAUT. MI]" AZIMUTH - "AZIMUTH [DEG]" BASE_HEIGHT - "BASE HEIGHT OF FEATURE [KFT]" HEIGHT - "HEIGHT OF FEATURE [KFT]" RADIAL_DIAM - "DIAMETER OF FEATURE ALONG RANGE AXIS FROM RADAR SITE [NMI]" AZ_DIAM - "DIAMETER OF FEATURE IN AZIMUTH ANGLE FROM RADAR SITE [DEG]" SHEAR - "SHEAR [E-3/S]" NEXRAD Level-III Storm Structure 'nx3structure' Dataset: WSR_ID - "NEXRAD or TDWR SITE ID" CELL_ID - "CELL ID UNIQUE TO RADAR SITE" RANGE - "RANGE [NAUT. MI]" AZIMUTH - "AZIMUTH [DEG]" VIL - "VERT. INTEG. LIQUID [KG/M**2]" MAX_REFLECT - "MAX REFLECTIVITY [DBZ]" NEXRAD Level-III Tornado Vortex Signature (TVS) 'nx3tvs' Dataset: WSR_ID - "NEXRAD or TDWR SITE ID" CELL_ID - "CELL ID UNIQUE TO RADAR SITE" RANGE - "RANGE [NAUT. MI]" AZIMUTH - "AZIMUTH [DEG]" MAX_SHEAR - "MAX SHEAR [E-3/s]" MXDV - "MXDV [KT]" NEXRAD Level-III Digital Mesocyclone Detection Algorithm 'nx3mda' Dataset: WSR_ID - "NEXRAD or TDWR SITE ID" CELL_ID - "CELL ID UNIQUE TO RADAR SITE" STR_RANK - "STRENGTH RANKING" SCIT_ID - "ID FROM SCIT ALGORITHM (USED IN OTHER NEXRAD PRODUCTS)" RANGE - "RANGE [NAUT. MI]" AZIMUTH - "AZIMUTH [DEG]" LL_ROT_VEL - "LOW LEVEL RV [KT]" LL_DV - "LOW LEVEL DV [KT]" LL_BASE - "BASE [KFT]" DEPTH_KFT - "DEPTH [KT]" DPTH_STMRL - "STMREL [PERCENT]" MAX_RV_KFT - "MAX RV HEIGHT [KFT]" MAX_RV_KTS - "MAX RV [KT]" TVS - "TVS [Y OR N]" MOTION_DEG - "MOTION DIR. [DEG]" MOTION_KTS - "MOTION SPEED [KTS]" MSI - "MSI" ----------------------------------------------------------------------------------- NCDC Documentation ----------------------------------------------------------------------------------- http://www.ncdc.noaa.gov/oa/documentlibrary/index.php?choice=dsi&searchstring=7000&submitted=1&submitted=Search ----------------------------------------------------------------------------------- Accuracy ----------------------------------------------------------------------------------- These NEXRAD Level III products (HI, M, SS, TVS) contain several possible sources of inaccuracies. The spatial accuracy of the data decreases with the range from the source NEXRAD Radar site. The general spatial accuracy of these data is 1 deg (theta) by 1 km (r), in the polar coordinate system centered on the Radar site where 'theta' is the angle from North and 'r' is the distance from the Radar site. This 1 deg x 1 km spacing equates to a range of spatial accuracies from 1 km (near Radar site) to 4 km (at 230 km from Radar site). Other factors contribute to the accuracy of these products and algorithms. The algorithms often rely on several different 'sweeps' at different elevation angles to determine hail, rotation, etc... Fewer sweeps are available at far distances from the NEXRAD site, resulting in less input data to the algorithm and possibly less accurate results. Mountainous areas can cause beam blockage at lower elevation angles, which compounds these issues. Furthermore, there are many adaptable parameters set by the Radar operator which are adjusted and 'tuned' for each weather situation or season. Variation of these values can cause additional inconsistencies. Even with these accuracy issues, the dataset is helpful in finding areas of bad weather and can be used in combination with other datasets (such as verified Storm Events) to add confidence to the values. More information about, and access to, the complete set of NEXRAD radar products is available at http://www.ncdc.noaa.gov/oa/radar.