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High-resolution moisture fields retrieved for the first time from both operational and research radars illustrate the low-level moisture variability associated with boundary layer processes and the prethunderstorm environment.^ everal national study groups (National Research V Council 1998;Emanuel et al. 1995; Dabberdt and J Schlatter 1996) have suggested that the lack of detailed, high-resolution water vapor measurements in the atmospheric boundary layer is one of the primary limiting factors in being able to predict the timing and location of convection initiation and to produce accurate quantitative precipitation forecasts (QPF). Humidity measurements from current operational surface station and radiosonde data provide discrete points of moisture information at 2-10 m AGL and ~250-m vertical resolution, respectively, but typically they are separated by distances of 10-100 km or greater. Moisture measurements can be retrieved over a higher spatial resolution from satellite data [e.g.; Moderate Resolution Imaging Spectroradiometer (MODIS) with 0.25-1-km resolution], but lack the high frequency of observations that are needed for the short-term forecasting of thunderstorms. Accurate measurements of moisture variability over high spatial and temporal resolution are needed for improvement in QPF and to forecast the onset of convection, which has shown to be thermodynamically sensitive to moisture and temperature perturbations in the boundary layer of only 1 g kg -1 and 1°C, respectively (Crook 1996).

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