Though weather is just one factor, it can really affect your travel plans, especially when you're planning an extended stay in Jangsan. The hottest months are usually August and July with an average temp of 74°F, while the coldest months are January and February with an average of 39°F. The rainiest months in Jangsan are July, August, June, and September, with each month seeing an average of 10 inches of rainfall.