September might be one of the most pleasant months for running in Belgium. The temperature usually ranges from about 11°C52°F to 19°C67°F, the wind averages 3.4m/s7.7mph and the daily precipitation is 2 mm0.1 inches.
More detailed information about the weather in Belgium can be found on the page for each city.
Please post about running and in English. Other posts may be removed.