From F1 Complete (http://www.f1complete.com/content/view/9991/900/) "Early forecasts show us that on Friday and Sunday of the race weekend we could have some Rain. Friday Sep 05 AM Rain Hi: 62° Lo: 48° Sunny skies. High 62F and low 48F. Air Quality: NA, UV Index: NA 95% Saturday Sep 06 Sprinkles Hi: 64° Lo: 51° Cloudy with drizzle. High 64F and low 51F. Air Quality: NA, UV Index: NA 95% Sunday Sep 07 Rain Hi: 65° Lo: 57° Rain. High 65F and low 57F. Air Quality: NA, UV Index: NA 95%"
Weather.com has 60% rain for Friday and Saturday, only 20% for Sunday. Wet qualy and hopefully dry race where the cars can do what they were designed to do at a place like Spa - GO FAST