Successful hydrologic modeling depends heavily on high-quality rainfall data sets. If hydrologists cannot determine what is coming into a watershed, there is little chance that any hydrologic model will accurately estimate what is coming out on a consistent basis. Hydrologists are frequently forced to use rainfall data sets derived from sparse rain gauge networks that poorly resolve critical rainfall features, leading to inadequate model results. Over the past several years, the modernizing National Weather Service, the Federal Aviation Administration, and the Department of Defense have installed a new nationwide network of weather radars, providing a rich suite of real-time meteorological observations. Radar rainfall estimates from the new radars cover vast areas at a spatial and temporal resolution that would be impossibly expensive to match with a conventional rain gauge network. Hydrologists can now literally see between the gauges and view truer representations of the spatial distribution of rainfall than ever before. Results from the analysis of the January 9–10, 1995, storms in Sacramento, California, show that gauge-adjusted radar rainfall estimates help resolve rainfall features that could not have been inferred from rain gauge analysis alone. Accurate estimates of the volume, timing, and distribution of rainfall helped create excellent modeling results. In Waco, Texas, radar rainfall estimates were used to improve the analysis of excess inflow and infiltration into city storm sewers. The radar rainfall analyses enabled modelers to account for inflow/infiltration variations down to the neighborhood level.