[Daily Japanese cedar pollen forecast in Sendai]

The forecast of daily Japanese cedar (Cryptomeria japonica) pollen counts was performed in Sendai in 1987, 1988 and 1989. The expected daily maximum temperature was used as a main determinative factor, and the term "pollen index", which is a ratio of a daily pollen count to the rest of the total seasonal pollen count, was devised and proved to be closely related to the daily maximum temperature. In 1987 and 1989, the total seasonal pollen count was very low, and daily pollen counts were in the lowest of three grades, except for a few days of the middle grade. In 1988, a fairly large number of pollen grains were observed, and forecasts of low grade were made for 28 days, middle grade for 25 days and high grade for 10 days, respectively. On the other hand, the actual daily pollen counts of low grade were 36 days, middle grade, 15 days, and high grade, 12 days, respectively. The accuracy of the forecast was 67% in 1988. The reasons for errors and the assignments for the forecast were discussed.