The beginning portions of the week actually look quite nice across Belgium, but that will chance significantly in the later half of the week. A large and deep low pressure trough is expected to drop southward into Scandinavia on Thursday, which will push a cold front through northern Europe, approximately in the Thursday night to Friday morning time frame. Rain is likely across Belgium on Thursday ahead of this front, mainly in the afternoon. Rain amounts on Thursday are expected to be around 4 mm or 0.15 inches. This probably won't be enough to cause a big impact on the practice sessions, but there could be some delays.
The cold front is expected to be passing through on Friday morning, shifting winds to a more northerly direction that will bring a colder air mass to the area. Temperatures will remain in the 40s on Friday. Periods of rain will continue as the upper level low pressure trough sits over the Baltic Sea. Rain amounts will likely be in the range of 2 to 5 mm (0.1 to 0.2 inches) on Friday.
A second cold front is expected to move into the area Friday night, which will drop temperatures even further, with lows in the 30s Saturday morning. It may be cold enough for precipitation to fall as snow. At this time, I don't think there will be any snow accumulation, as temperatures should remain just above freezing at the surface, and any snow should change to rain by midday. Wet and cold conditions for the race will be a challenge for teams and fans to deal with on Saturday. I expect that tire temperatures will be the story of the day. Forecasting rain amounts this far out is difficult, but amounts in the range of 3 to 6 mm (a tenth to a quarter inch) appear most likely at this time on Saturday.
Hopefully I can bring better news with the next forecast update, which I expect to have posted on Wednesday morning.