We focus on the Probable Maximum Precipitation (PMP) over the Upper Tone River basin, through maximization of weather conditions. In order to evaluate vertical and horizontal distributions of weather conditions during heavy precipitations, Grid point value (GPV) data from meso-scale objective analysis is used. The results are summarized as follows: (1) Moisture fluxes have higher correlation with typhoon rainfalls than precipitable waters which are the basic index to maximize precipitation under the WMO method. (2) Moisture fluxes between 850 and 800 hPa have high correlation with the data observed at the surface. Converted past heavy surface moisture fluxes into moisture fluxes between 850 and 800 hPa showed high correlation coefficient of more than 0.8 with rainfall by major typhoons. (3) PMP was calculated from the past maximized moisture flux ratio for major typhoon rainfalls, and it exceeds the maximum observed rainfall in the area.
