Some moisture will continue to wrap around the counter-clockwise circulation of the low into Friday, which will keep a good chance of showers in the forecast as cars hit the track. The good news is that any rain on Friday is expected to be light. It may only be on/off sprinkles. The total amount of rain on Friday will likely be under a tenth of an inch, so I expect that the impact on racing will be low. Some wet tires will probably have to be used at some point, probably for the morning sessions, but I don't foresee significant weather delays or cancellations. If you're attending the race, you may want to bring an umbrella. With a northwest wind and cloudy skies, temperatures will be pretty cool all day, mainly in the 50s.
Saturday looks like a great day to be at the track, and any chance of rain will end as the low moves farther away. Pleasant temperatures in the upper 60s are expected, with sunshine peeking through the clouds at times.