A cold front is expected to cross through St. Louis on Thursday night. It will be close enough to the track and with enough uncertainty about its speed that I will keep a small chance of rain in the forecast for Friday morning. But since on-track activity does not start until the afternoon, no impact is expected. Behind the front, drier air will be building in from the north through the day, and with mostly cloudy skies, high temperatures will be quite comfortable in the lower 80s.
As the front is expected to stall across southern Missouri on Saturday and high pressure over the Great Lakes region will extend across Illinois, Sunday will stay dry. Previous model runs had shown a weak disturbance approaching Saturday, but that no longer appears to be the case. With more sunshine expected, highs on Saturday will reach the mid 80s, but humidity will be comfortably low. Temperatures during the race will be in the 75 to 80 range.
I will be traveling to VIR tomorrow for the IMSA race this weekend, and Friday may be a busy day of providing weather support to the track, so I may not get to update this forecast until Friday night.