In certain circumstances, millimeter-wavelength Doppler radar velocity spectra can be used to estimate the microphysical composition of both phases of mixed-phase clouds. This distinction is possible when the cloud properties are such that they produce a bimodal Doppler velocity spectrum. Under these conditions, the Doppler spectrum moments of the distinct liquid and ice spectral modes may be computed independently and used to quantitatively derive properties of the liquid droplet and ice particle size distributions. Additionally, the cloud liquid spectral mode, which is a tracer for clear-air motions, can be used to estimate the vertical air motion and to correct estimates of ice particle fall speeds.A mixed-phase cloud case study from the NASA Cirrus Regional Study of Tropical Anvils and Cloud Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) is used to illustrate this new retrieval approach. The case of interest occurred on 29 July 2002 when a supercooled liquid cloud layer based at 5 km AGL and precipitating ice crystals advected over a ground measurement site. Ground-based measurements from both 35-and 94-GHz radars revealed clear bimodal Doppler velocity spectra within this cloud layer. Profiles of radar reflectivity were computed independently from the liquid and ice spectral modes of the velocity spectra. Empirical reflectivitybased relationships were then used to derive profiles of both liquid and ice microphysical parameters, such as water content and particle size. Although the ice crystals extended down to a height of 4 km, the radar measurements were able to distinguish the base of the cloud liquid at 5 km, in good agreement with cloud-base measurements from a collocated micropulse lidar. Furthermore, radar-derived cloud liquid water paths were in good agreement with liquid water paths derived from a collocated microwave radiometer.Results presented here demonstrate the ability of the radar to both identify and quantify the presence of both phases in some mixed-phase clouds. They also demonstrate that, in terms of radar reflectivity, the ice component of mixed-phase clouds typically dominates the radar signal, while in terms of mean Doppler velocity, the liquid component can make a significant contribution. The high temporal resolution, 94-GHz Doppler radar observations were able to reveal a periodic cloud-top updraft that, combined with horizontal wind speeds, suggests a horizontal scale for the in-cloud circulations.

During Northern Hemisphere winters, the West Coast of North America is battered by extratropical storms. The impact of these storms is of paramount concern to California, where aging water supply and flood protection infrastructures are challenged by increased standards for urban flood protection, an unusually variable weather regime, and projections of climate change. Additionally, there are inherent conflicts between releasing water to provide flood protection and storing water to meet requirements for the water supply, water quality, hydropower generation, water temperature and flow for at-risk species, and recreation. To improve reservoir management and meet the increasing demands on water, improved forecasts of precipitation, especially during extreme events, are required. Here, the authors describe how California is addressing their most important and costliest environmental issue-water management-in part, by installing a state-of-the-art observing system to better track the area's most severe wintertime storms.

Test beds have become an integral part of the weather enterprise, bridging research and forecast services by transitioning innovative tools and tested methods that impact forecasts and forecast users. O ver roughly the last decade, a variety of "test beds" have come into existence focused on high-impact weather and the core tools of meteorology-observations, models, and fundamental understanding of the underlying physical processes. They have entered the proverbial "valley of death" between research and forecast operations (NAS 2000), Develop and introduce new ideas, data, etc. Input Revise and iterate Experiment and demonstrate End testing Output Test and refine loop V Assess impacts and evaluate and have survived. This paper provides a brief background on how this happened; summarizes test bed origins, methods, and selected accomplishments; and provides a perspective on the future of test beds in our field. Dabbert et al. (2005) provides a useful description of test beds from early in their development and Fig.

Recent and historical events illustrate the vulnerabilities of the U.S. west to extremes in precipitation that result from a range of meteorological phenomena. This vision provides an approach to mitigating impacts of such weather and water extremes that is tailored to the unique meteorological conditions and user needs of the Western U.S. in the 21st Century. It includes observations for tracking, predicting, and managing the occurrence and impacts of major storms and is informed by a range of userrequirements, workshops, scientific advances, and technological demonstrations. The vision recommends innovations and enhancements to existing monitoring networks for rain, snow, snowmelt, flood, and their hydrometeorological precursor conditions, including radars to monitor winds aloft and precipitation, soil moisture sensors, stream gages, and SNOTEL enhancements, as well as entirely new observational tools. Key limitations include monitoring the fuel for heavy precipitation, storms over the eastern Pacific, precipitation distributions, and snow and soil moisture conditions. This article presents motivation and context, and describes key components, an implementation strategy, and expected benefits. This document supports a Resolution of the Western States Water Council for addressing extreme events.

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