You'll likely spend much of your trip indoors, but if you're planning to venture beyond the casino, taking a look at local weather data can help you. The hottest months are usually August and July, with an average temperature of 21°C, while the coldest months are January and February, with an average of 0°C. The rainiest months in Yamagata are July, August, September and June, with each month seeing an average of 177 mm of rainfall.