NEXRAD or Nexrad (Next-Generation Radar) is a network of 158 high-resolution Doppler weather radars operated by the National Weather Service, an agency of the National Oceanic and Atmospheric Administration (NOAA) within the United States Department of Commerce. Its technical name is WSR-88D, which stands for Weather Surveillance Radar, 1988, Doppler. NEXRAD detects precipitation and atmospheric movement or wind.

The daily NEXRAD precipitation data are quality-controlled, multi-sensor (radar and rain gauge) precipitation estimates obtained from National Weather Service (NWS) River Forecast Centers (RFCs). The "observed" precipitation data is a byproduct of the National Weather Service (NWS) operations at the 12 RFCs, and is displayed as a gridded field with a spatial resolution of 4x4 kilometers over a 24-hour time period (NWS 2008).

East of the Continental Divide, the RFCs derive the "observed" precipitation field using a multisensor approach. Hourly precipitation estimates from WSR-88D NEXRAD are compared to ground rainfall gauge reports, and a bias (correction factor) is calculated and applied to the radar field. The radar and gauge fields are combined into a "multisensor field", which is quality controlled on an hourly basis. In areas where there is limited or no radar coverage, satellite precipitation estimates (SPE) can be incorporated into this multisensor field. The SPE can also be biased against rain gauge reports (NWS 2008).

In mountainous areas west of the Continental Divide, a different method is used to derive the "observed" data. Gauge reports are plotted against long term climatologic precipitation (PRISM data), and derived amounts are interpolated between gauge locations (NWS 2008).

Studies have shown that algorithms which combine several sensor inputs such as radar, gauge, and satellite data yield more accurate precipitation estimates than those which rely on a single sensor such as radar-only, gauge-only, or satellite-only. Although the NEXRAD precipitation product is not perfect, this dataset covers the lower 48 states and it is one of the best sources of timely, high resolution precipitation information available (NWS 2008).

NEXRAD data was first introduced in Crop Explorer in early 2008 and FAS crop analysts have noticed that it truly has superior data quality compared to the other global precipitation data sets that cover the United States.