You are round tripping it? 660 miles in one day? Hardcore.
You have two choices.
1. Go to St. Louis, make the best of it if the game is cancelled. Go get a steak at Shannon's, and laugh it off as one of life's unpredictable things. Part of the adventure.
2. Stay home, make the best of it if the game is played. Take the gas money and money spent at the park and go buy some steaks, and cook them on the grill. With gas prices, you could probably get something nice from mlb.com. Maybe that jersey you have been looking at.
The key is to make a decision and go with the flow. I can't help with that. If you need more info than a garden variety forecast, go here to see the actual computer models:
http://weather.unisys.com/ngm/index.html
The one model I saw had a dark blue line through St. Louis at 6pm on Wednesday (it says 0Z Thursday but we are 6 hours off of GMT).