The initial forecast that I made on Monday still seems to be generally on track, but I've made a few tweaks for today's update. The main change has been to add a slight chance of rain on Sunday afternoon, however I still expect that impacts on the race will be very low.
Rain associated with a deep upper level trough and surface cold front is still expected to move across England late tonight and into Thursday. Although it will likely be wet for scrutineering, the rain will be long gone by the time on-track activity begins on Friday. Behind the departing trough and cold front, temperatures on Friday will be cooler than normal (the normal high is 75 F/24 C), with a west wind at 10 to 15 mph (8-16 km./h).
Another low pressure system will be tracking east between Iceland and Scotland on Saturday, but it will be too far north and too weak to have any real impact on Silverstone. A weak ridge in the upper levels will build slightly over southern England, which should provide for some periods of sunshine and warmer temperatures in the mid 70s F/mid 20s C.
Yet another fast-moving low pressure system will track between Iceland and Scotland on Sunday, but it appears that this one will be farther south and a bit stronger than the one on Saturday. It will shift winds to a more southwest direction, and bring a little more moisture into central England. This may produce some light rain at Silverstone in the afternoon. However, it appears that it will be light rain, with maybe only a couple hundredths of an inch expected (around 0.5 mm) at most. I am keeping the impact level at "Green" as I don't expect there to be enough rain for any weather-related interruptions.