NEXRAD

Deployed from March to August 2008 with all level II data,[16] the Super Resolution upgrade permitted the capability of the radar to produce much higher resolution data. Under legacy resolution, the WSR-88D provides reflectivity data at 1 km (0.62 mi) by 1 degree to 460 km (290 mi) range, and velocity data at 0.25 km (0.16 mi) by 1 degree to a range of 230 km (140 mi). Super Resolution provides reflectivity data with a sample size of 0.25 km (0.16 mi) by 0.5 degree, and increase the range of Doppler velocity data to 300 km (190 mi). Initially, the increased resolution is only available in the lower scan elevations. Super resolution makes a compromise of slightly decreased noise reduction for a large gain in resolution.[17]

The improvement in azimuthal resolution increases the range at which tornadic mesoscale rotations can be detected. This allows for faster lead time on warnings and extends the useful range of the radar. The increased resolution (in both azimuth and range) increases the detail of such rotations, giving a more accurate representation of the storm. Along with providing better detail of detected precipitation and other mesoscale features, Super Resolution also provides additional detail to aid in other severe storm analysis. Super Resolution extends the range of velocity data and provides it faster than before, also allowing for faster lead time on potential tornado detection and subsequent warnings.[18]

Non-Polarimetric Radar

Polarimetric Radar

WSR-88D sites across the nation have been upgraded to polarimetric radar, which adds a vertical polarization to the traditional horizontally polarized radar waves, in order to more accurately discern what is reflecting the signal. This so-called dual polarization allows the radar to distinguish between rain, hail, and snow, something the horizontally polarized radars cannot accurately do. Early trials showed that rain, ice pellets, snow, hail, birds, insects, and ground clutter all have different signatures with dual polarization, which could mark a significant improvement in forecasting winter storms and severe thunderstorms.[19] The deployment of the dual polarization capability (Build 12) to NEXRAD sites began in 2010 and was completed by the summer of 2013. The radar at Vance Air Force Base in Enid, Oklahoma was the first operational WSR-88D modified to utilize dual polarization technology. The modified radar went into operation on March 3, 2011.[20]

When the NEXRAD system was initially implemented, the radar automatically scanned all scan angles in a Volume Coverage Pattern, even if the highest scan angles were free of precipitation. As a result, in many cases when severe weather was farther from the radar site, forecasters could not provide as timely severe weather warnings as possible. The Automated Volume Scan Evaluation and Termination (AVSET) algorithm[21] helps solve this problem by immediately ending the volume scan when precipitation returns at higher scan angles drop below a set threshold (around 20 dBZ). This can often allow for more volume scans per hour, improving severe weather detection without the need for hardware upgrades[22][23] AVSET was initially deployed in RPG build 12.3, in Fall of 2011.

One of the primary weaknesses of the WSR-88D radar system was the lack of frequency of base (0.5 degree) scans, especially during severe weather. Forecasters, and TV viewers at home, often had access to images that were four or five minutes old, and therefore had inaccurate information. TV viewers at home could be lulled into a false sense of security that a tornado was farther away from them than it really was, endangering residents in the storm's path. The Supplemental Adaptive Intra-Volume Low-Level Scan (SAILS) technique, deployed with Build 14 in the first half of 2014, allows operators the option to run an additional base scan during the middle of a typical volume scan.[24] With one SAILS cut active on VCP 212, base scans occur about once every two and a half minutes, with more frequent updates if AVSET terminates the volume scan early.

Multiple Elevation Scan Option for Supplemental Adaptive Intra-Volume Low-Level Scan (MESO-SAILS) is an enhancement to SAILS, which allows the radar operator to run one, two or three additional base scans during the course of a volume scan, per the operators request.[12] During June 2013, the Radar Operations Center first tested SAILSx2, which adds two additional low-level scans per volume. It was executed for approximately 4.5 hours and during the testing, an Electronics Technician observed the pedestal/antenna assembly's behavior. No excessive wear was noted. Two days later, SAILSx3 was executed, which added 3 additional low-level scans to a volume. During this 1.5 hour test of SAILSx3, a ROC Radar Hardware Engineer accompanied the ROC Electronics Technician to observe the antenna/pedestal assembly. Again, no excessive wear was noted.[25] MESO-SAILS was deployed with Build 16.1, in spring of 2016.

Mid-Volume Rescan of Low-Level Elevations (colloquially known as M.R.L.E.) is a dynamic scanning option for the WSR-88D derived from MESO-SAILS,[26] a separate scanning option implemented in NEXRAD RPG 14.0, in the Spring of 2014.[27]

During quasi-linear convective systems (QLCS), colloquially known as squall lines, the detection of mesovortices, which generate at 4,000 to 8,000 feet above ground level,[28] is not always possible with SAILS cuts, as the base 0.5 degree scan travels below the formation of mesovortices at closer distances to the radar. MRLE consecutively scans either the two, three or four lowest scan angles during the middle of a typical volume scan, allowing more frequent surveillance of mesovortex formation during QLCS events.[29] MRLE will be deployed on a non-operational basis in RPG 18.0 in spring of 2018, with possible operational deployment with RPG 19.0, if proven useful or of importance.

Deployment was anticipated by the Radar Operations Center to commence in October 2017, along with the RPG 18.0 build, on a non-operational basis. The scanning option will only be available for use with Volume Coverage Patterns 21, 12, 212, and additionally 215.[30] If proven to be significant in terms of warning dissemination, MRLE will deploy operationally nationwide with RPG 18.0, planned for 2018.

Spin-up tornado associated with a QLCS as seen from a nearby Doppler weather radar, which often goes unseen.

The concept of MRLE derives from the need of more frequent low-level scans during quasi-linear convective systems (QLCSs). During QLCSs, it is not uncommon for brief and otherwise un-noticeable mesovortices to spawn at points along the line.[31] Due to untimely radar data and time being taken to complete the entire volume, these vortices often spawn without warning or prior notice. With MRLE, the operator has the choice between 2 and 4 low-level scans. Unlike MESO-SAILS, which scans at one angle and can only do up to 3 low-level scans per volume, MRLE scans at 4 possible angles, and can cut into a volume up to 4 times, depending on the operators choice. The angles are as follows, alongside their respective scan frequencies:

• MRLEx2 = 0.5° and 0.9° elevations
• MRLEx3 = 0.5°, 0.9° and 1.3° elevations
• MRLEx4 = 0.5°, 0.9°, 1.3° and 1.8° elevations[32]

The operator can not use MESO-SAILS alongside MRLE simultaneously. If one is selected while the other is active, the NEXRAD algorithms will automatically set the other "off".

Started on March 13, 2013, the SLEP, or Service Life Extension Program, is an extensive effort to keep and maintain the current NEXRAD network in working order for as long as possible. These improvements include Signal Processor upgrades, Pedestal upgrades, Transmitter upgrades, and shelter upgrades. The program is anticipated to be finished by 2022, which coincides with the beginnings of a nationwide implementation of Multi-function Phased Array Radars (see below).[33]

The NEXRAD site located in Cayey, Puerto Rico was destroyed during the passage of Hurricane Maria through the region in September 2017.[40] In addition to a neighboring Terminal Doppler Weather Radar (TDWR) site that was rendered temporarily inoperable but ultimately survived, the Department of Defense deployed two short-range X-band radars on the island to provide radar coverage until the FAA-maintained NEXRAD site was restored.[41] In June 2018, this NEXRAD radar site was restored to fully operational condition and was reinforced with several lightning rods and secured with a stronger fiberglass dome that included using more than 3,000 bolts.[42]

On August 27, 2020, the NEXRAD radar site located in Lake Charles, Louisiana, was destroyed by Hurricane Laura as the eye of the Category 4 storm—which packed wind gusts recorded around 135 mph (217 km/h) in the city—passed over the site after it made landfall. NEXRAD radars based in Houston, Shreveport and Fort Polk were used to fill gaps in radar coverage within portions of Southwestern Louisiana until the Lake Charles site was rebuilt; the NWS Radar Operations Center also deployed a SMART-R vehicle on loan from the University of Oklahoma to provide supplemental radar data on Hurricane Delta in advance of its track into the region (nearly paralleling that of Hurricane Laura) in late October.[43][44][45] Operational service to the Lake Charles NEXRAD radar site was restored in January 2021, following a four-month, $1.65-million reconstruction project that included the replacement of the radome and internal equipment and repairs to the station's radome pedestal, tower, fence and equipment shelters.[46]

The National Weather Service keeps a list of upcoming improvements to the WSR-88D system.[47]

Multi-Function Phased Array Radar during installation in Norman, Oklahoma, 2003

Beyond dual-polarization, the advent of phased array radar will probably be the next major improvement in severe weather detection. Its ability to rapidly scan large areas would give an enormous advantage to radar meteorologists.[48] Its additional ability to track both known and unknown aircraft in three dimensions would allow a phased array network to simultaneously replace the current Air Route Surveillance Radar network, saving the United States government billions of dollars in maintenance costs.[48][49] The National Severe Storms Laboratory predicts that a phased array system will eventually replace the current network of WSR-88D radar transmitters.[50]

NEXRAD data is used in multiple ways. It is used by National Weather Service meteorologists and (under provisions of U.S. law) is freely available to users outside of the NWS, including researchers, media, and private citizens. The primary goal of NEXRAD data is to aid NWS meteorologists in operational forecasting. The data allows them to accurately track precipitation and anticipate its development and track. More importantly, it allows the meteorologists to track and anticipate severe weather and tornadoes. Combined with ground reports, tornado and severe thunderstorm warnings can be issued to alert the public about dangerous storms. NEXRAD data also provides information about rainfall rate and aids in hydrological forecasting. Data is provided to the public in several forms, the most basic form being graphics published to the NWS website. Data is also available in two similar, but different, raw formats. Available directly from the NWS is Level III data, consisting of reduced resolution, low-bandwidth base products as well as many derived, post-processed products; Level II data consists of only the base products, but at their original resolution. Because of the higher bandwidth costs, Level II data is not available directly from the NWS. The NWS distributes this data freely to Amazon Web Services[51][52] and several top-tier universities, which in turn distribute the data to private organizations.[53]