Precipitation particles are mainly formed by ice-crystal process, warm rain process is only observed in tropical area. Chemical substances are scavenged by precipitation particles under the in-cloud process and below-cloud process. The ratios of Cｌ^-/Na⁺ and Mg²⁺/Na⁺ in all the winter precipitation samples collected at Tohkamachi are nearly equal to that found in sea water. These results suggest that sources other than sea water can be considered negligible. It is concluded that sea water is the predominant source of Na⁺, Cl^-, and Mg²⁺ in the winter precipitation. The origin of NO₃^- and NH₄⁺ in the winter precipitation samples collected at Tohkamachi is considered to be non sea salt. The origins of SO₄^2- and Ca²⁺ are both sea salt and non sea salt. NO₃^- and nssSO₄^2- are the acidic materials and decline pH value of the winter precipitation. NH₄⁺ and nssCa²⁺ are the neutralization materials of acid precipitation. Synoptic meteorological conditions of winter precipitation at Tohkamachi are classified into three types. These three types consist of the winter monsoon, a cyclone positioned over the Sea of Japan, and a cyclone located over the Pacific Ocean near the main island of Japan. Sea salt particles contained in cloud droplets are collected by snow crystals through the in-cloud scavenging process. The higher the height of the convective mixing layer, the greater the rate of collection of the sea salt particles by the snow crystals. The duration of the convective mixing affects the rate of collection of the sea salt particles by the snow crystals. A correlation can be observed between the height of the convective mixing layer and the concentration of Na⁺ in winter precipitation at Tohkamachi. And a mutual relationships between the temperatures at the top of convective mixing layer and the δ¹⁸O values in winter precipitation samples are observed for each weather condition that produces winter precipitation. The regression equations differ for each weather condition. Winter precipitation samples formed during the winter monsoon have larger δ¹⁸O values than these formed under other conditions at the same temperature. The δ¹⁸O values of samples precipitated under conditions when the cyclone is positioned over the Pacific Ocean are the smallest. The cyclone system that passes over the Pacific Ocean has a relatively long life time, and precipitates heavy isotopic particles during the synoptic times associated with this period in the south-west area of Japan. As the result of this phenomena, the samples precipitated in Tohkamachi under conditions of the cyclone positioned over the Pacific Ocean are considered to have a relatively small δ¹⁸O values.