Journal
JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN
Volume 96A, Issue -, Pages 201-220Publisher
METEOROLOGICAL SOC JAPAN
DOI: 10.2151/jmsj.2018-028
Keywords
VIL; nowcast; volume scan; XRAIN; localized heavy rainfall
Categories
Funding
- National Institute for Land and Infrastructure Management (NILIM) of Japan
- Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS) program
- Integrated Promotion of Social Reform and Research and Development (JST/MEXT)
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This paper reports the development of a very-short-range nowcast system, VIL Nowcast, which aims to provide precise forecasts of imminent rainfall, and in particular, heavy and localized events. The system is based on the vertically integrated liquid water content (VIL), which is estimated from three-dimensional radar observations as well as the 1-minute-resolution rainfall map obtained from the X-band polarimetric (multi-parameter) RAdar Information Network (XRAIN), to predict rainfall amounts over 10 minutes periods that extend to 10-60 minutes into the future. The spatial resolution of VIL Nowcast was 500 m, and nowcasts were produced at a temporal resolution of 5 minutes. Three precipitation events, of which two were isolated storms and one was a synoptic storm, were used as case studies to verify the model. The performance of VIL Nowcast was evaluated against the XRAIN radar rainfall data and an existing rainfall-rate nowcast system using the same advection scheme. The scope of the evaluation was limited mainly to the first prediction for 10 minutes ahead. It was found that VIL Nowcast showed a small, statistically significant improvement over the entire precipitation event, although its skill decreased at longer lead times and at higher thresholds. The key findings of this study are: (1) VIL Nowcast appears capable of generating skillful forecasts at short lead times, even for very localized heavy rainfall; (2) VIL Nowcast can reduce the time lag in the rainfall-rate nowcast system at initiation and peak precipitation; and (3) this system may improve the accuracy of heavy rainfall alerts provided for public activities and emergency alarms.
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