There will be a large upper level trough across the area on Thursday and Friday, which will produce cloudy and cool weather with scattered showers. Thunderstorms do not appear to be a threat at the track, and at this time I do not expect that the rain on Friday will be very heavy. It looks like there will be mainly light showers that are on and off at times through the day, perhaps occurring with more frequency in the afternoon than the morning.
The chance of rain will continue Friday night, but I expect that the trough will be moving fast enough that the chance of rain will end before the TA2 race on Saturday morning at 10:55 am. This is one part of the forecast that I'm not very confident about right now - it is possible that a few showers could linger into Saturday morning, but I'm going with a dry day for now because I don't think it will have an impact while there is action on the track. Clouds will be decreasing through the day, with mostly sunny skies developing in the afternoon. Despite the sunshine, a north wind will keep temperatures cool, with highs in the mid 60s.
Sunday looks great as a strong high pressure ridge builds into the area. While morning temperatures will be quite cool, in the 40s, sunny skies will bring temperatures up to the upper 60s in the afternoon.