Today will feature increasing clouds, but it will be warm, with highs in the upper 70s. There is a chance of showers beginning in the evening and continuing overnight, but it shouldn't interfere with any on track activity. They may linger into Friday morning as well, but there should be decreasing clouds Friday afternoon, making for an overall nice day.
Rain is expected to spread into the area late Saturday morning to early afternoon. Rain may be heavy at times in the afternoon and evening, and continue through the night. Total rainfall amounts through Saturday night are expected to be from a half inch to one inch. The low pressure system will be departing to the northeast on Sunday, but moisture wrapping around the low will keep light showers on and off through the day. I think the majority of the showers will be in the morning, but there will still be some around in the afternoon. Again, I think Sunday's rain will be light, with amounts less than a tenth of an inch.
You can use the TUSC Radar link at the top of the website to keep an eye on the rain through the event.