Advantages
A NEXRAD weather radar currently used by the National Weather Service (NWS) is a 10 cm wavelength (2700-3000 MHz) radar capable of a complete scan every 4.5 to 10 minutes, depending on the number of angles scanned, and depending on whether or not MESO-SAILS[7] is active, which adds a supplemental low-level scan while completing a volume scan. Its resolution is 0.5 degrees in width and 250 metres (820 ft) in range. The non-ambiguous radial velocity is 62 knots (71 mph; 115 km/h) up to 230 kilometres (140 mi) from the radar.[1][4]
The range resolution of the TDWR is nearly twice that of that classic NEXRAD scheme. This will give much better details on small features in precipitation patterns, particularly in thunderstorms, in reflectivity and radial velocity. However, this finer resolution is only available up to 135 kilometres (84 mi) from the radar; beyond that, the resolution is close to that of the NEXRAD. However, since August 2008, oversampling on NEXRAD has increased its resolution in lower elevations in reflectivity data to 0.25 km (0.16 mi) by 0.5 degree, and increased the range of Doppler velocity data to 300 km (190 mi).[8][9] This lessens the advantages of TDWR for those elevations.
Shortcomings
The TDWRs and NEXRADs complement each other with overlapping coverage, each designed to optimally view different airspace regimes. TDWR's rapid update rate over short range (55 nmi range) captures microscale weather events quickly in terminal airspace. NEXRAD is a long range radar (200 nmi range) designed to serve multiple en route functions at high altitude, above terminal airspace, and far between terminals. NEXRAD's slower update rate covering a wider volume, captures mesoscale weather events. The shorter 5 centimetres (2.0 in) wavelength, which is closer to the size of a raindrop than the 10 centimetres (3.9 in) wavelength, is partially absorbed by precipitation. This is a serious drawback to using TDWR, as the signal can be strongly attenuated in heavy precipitation. This attenuation means that the radar cannot "see" very far through heavy rain and could miss severe weather such as strong thunderstorms which may contain the signature of a tornado, when there is heavy rain falling between the radar and that storm. When heavy rain is falling on the radome, the range of the TDWR is further limited.[1][4] Finally, hail in a thunderstorm scanned by a TDWR can entirely block the signal as its size is larger than the wavelength.[1][4]
A second problem is the smaller non-ambiguous radial velocity or Nyquist velocity. In the case of the TDWR, this means the velocity of precipitations moving at a speed beyond 30 knots (35 mph; 56 km/h) away or toward the radar will be analyzed incorrectly because of aliasing. Algorithms to correct for this do not always yield the proper results. NEXRAD has a threshold that is twice as high (62 knots (71 mph; 115 km/h)) and thus less processing and interpretation are needed. Because of this, the resolution of radar reflectivity for small scale features such as mesocyclones might be better in TDWR, but the velocity resolution may be worse, or at the very least incorrectly analyzed.
Thus, it is best to use the TDWR in conjunction with a traditional NEXRAD nearby to ensure that nothing is missed. In contrast to NEXRAD, which has national coverage of the contiguous United States (although with some holes due to terrain), TDWR has sporadic coverage meant for major airports. While certain areas of the country (the Northeast megalopolis, the states of Ohio and Florida, and the southwestern quarter of Tornado Alley in Oklahoma and Texas) have a high density of TDWR units, others (the entire West Coast, the northern Great Plains and Rocky Mountains, portions of the Deep South, and a stretch running from northern Pennsylvania through upstate New York and into northern New England) have no TDWR coverage at all.