BEIJING, Oct. 20 -- "It's a fine day today and we suggest you to enjoy the fall foliage on mountains 200 meters above the sea level." Beijing Meteorological Bureau launched a new service on Friday giving daily "index on viewing fall foliage," the Morning Post reported.

The five-grade index is based on weather conditions and the actual changes of color of the leaves, helping tourists to make plans, with grade one being the best.

This weekend, for instance, with cold air from the north-west chilling the city, we can expect beautiful red leaves, especially on mountains 200 meters above the sea level. In this case, the index is grade two.

Mountains around Beijing are mainly covered by smoke trees and maple trees. The leaves on these trees turn red in cold weather, reflecting the loss of chlorophyll and the remaining of anthocyanin. Sudden fall of temperature accelerates the changes.

Every year from late October to mid November is the prime time to view red leaves covering the mountains.

Popular sites include the Fragrant Hill and the Badaling section of the Great Wall.

(Source: CRIENGLISH.com)