The season's first fall foliage appeared on Mount Seorak in Gangwon Province on Monday. The Gangwon Regional Meteorological Administration said it recorded the season's first fall foliage on the 1,708-meter mountain. This year's arrival came four days earlier than last year and matched the long-term average date. Weather authorities define "first foliage" as the point when about 20 percent of a mountain's decidous leaves change color, from the summit downward. Fall foliage on Mount Seorak is projected to reach its peak in mid-to-late October. Peak color occurs when approximately 80 percent of the foliage on a mountain has turned color. Foliage peaked on Oct. 24 last year, compared with the long-term average of Oct. 17. The color change is expected to accelerate as cold air moves down from the north late this week, dropping morning lows nationwide into single digits starting Thursday. The agency forecast morning lows of 6 to 17 degrees Celsius and daytime highs of 20 to 24 degrees nationwide from Thursday through Saturday. Visitors can check current foliage conditions for 21 major mounta