Today marks five days in a row with high temperatures in the 80’s. Pretty good for July. And it appears we’ll see another 2-4 this week. The Storm Prediction Center has placed us under a slight risk area for “tomorrow” but don’t worry about that. The outlook is for Mon 8A.M. until Tue 8 A.M. The small concern is for the last 6-8 hours of that time.
All three models (GFS, NAM and HIRES Nam) are in good agreement for that 8PM-8AM period tomorrow night. But they differ before and after that. All three bring a weak upper level disturbance over us around 8 A.M. Monday, but there won’t be much moisture with it so the chance for rain will be very low. That system will bring in plenty of moisture so after the morning clouds move away, we’ll see a mostly sunny, hot, and humid afternoon. That’s when the first difference shows up. The GFS is fairly generous with a round of thunderstorms after 6P.M. The NAM models are basically ignoring any major chance for thunderstorms until after midnight. The “official” forecast which most broadcasters use has a 50% t-storm chance tomorrow. I’d say 20% is more realistic.
All three models bring in a stronger upper air system tomorrow night…best timing for Louisville area will be Midnight through Noon Tuesday. Moisture will be plentiful and energy abundant, so a large cluster of t-storms/rain appears likely during that time frame. If we’re going to see any severe storms it would be around 2-8A.M. Historically, those are hours fade and/or die, Let’s just hope we get some good soaking rain.
After Noon Tuesday, the GFS once again breaks away from the NAM models. The NAM essentially has everything wrapped up by Noon with cooler, drier returning for a few days. The GFS slows the system to allow another (fairly weak) outbreak of showers/t-storms late afternoon/evening.

Here’s how I see it in forecast form:
Tonight: becoming partly cloudy after midnight. Warm, with a low near 70.
Monday: mostly cloudy early followed by a sunny, hot and humid…high…92.
20% chance for a late afternoon thunderstorm.
Monday night: Showers and thunderstorms likely, especially after midnight.
low near 67.