On Thursday, moisture will begin to spread into the area from the south as a low pressure system tracks across Ontario. The question about Thursday is how quickly rain will move into the area. Over the past few days, most of the models have favored the afternoon and evening hours for rain, and this timing seems to be on track. Most of the rain may come after the practice sessions for the day are done, so I only have a low impact for Thursday even though the rain chance before sunset is high. Rain amounts around a tenth seem likely before sunset. More rain is expected after sunset, possibly another quarter of an inch.
Friday continues to be the least confident day for me as Watkins Glen will be between low pressure systems, and model agreement is poor. Although the atmosphere will be very moist, there isn't a strong mechanism in the atmosphere to produce lift for rain, and this is when the models tend to do poorly. At this time, I think there is about a 50/50 chance of seeing rain at some point in the day. With some sunshine possible at times, temperatures should warm up into the mid 80s with winds from the southwest at 10-15 mph.
The second low pressure system will track across the Great Lakes and Ontario on Friday night and Saturday, with its trailing cold front moving through Saturday night. With the warm, moist air mass in place and lift provided by the approaching front, I expect numerous showers and thunderstorms around the track on Saturday. Timing of the best rain chances is tough to pinpoint this far out, as it looks like there could be storms at any time during the day. Rainfall amounts could be somewhere in the range of 0.25 to 0.75 inches, and the rain could be heavy at times. For this reason, I've ranked the impact on Saturday as moderate. I expect there will at least be some delays to the on track action, with some cancellations possible.
The front will move east of Watkins Glen Saturday night, but the upper level trough will lag behind slightly, which is why I have a slight chance of rain mentioned Sunday morning. I don't think any rain on Sunday will have an impact on the race, as it will be light if it even happens at all. Clouds will be decreasing through the race, and it may be mostly sunny by the end, with temperatures getting close to 80 degrees.
We'll have our radar link at the top of the page ready to go for Watkins Glen by Thursday.