A week ago I wrote that the Thursday – Tuesday period (9/6 – 9/10) should have an increased rain chance due to a flow of deep moisture from the Gulf. The forecast reasoning was sound but the persistent extratropical low that may be transitioning into a tropical depression has pushed the best chance for rain for the Mid-South back a few days.
The current radar image of the U.S. shows a front extending north and west of KY. The current run of the GFS shows why the rain has had a hard time pushing into our area. The upper level low, currently located a few hundred miles east of Florida, has caused the ridge located over the Mid-Atlantic to elongate, which has shut off the flow of Gulf moisture to the Mid-South and has focused Gulf moisture over the southern plains. Even by Sunday afternoon, the front has not moved appreciably from where it is now and the lack of low-level moisture (look at the 850 mb wind flow) has reduced the precipitation associated with the front.
The GFS suggests that a shortwave (500 mb map) will eject from the Rockies on Monday and by Tuesday this shortwave will bring a return flow of Gulf moisture to the region that should result in widespread showers/t-storms over the Mid-South. A second front on Thursday/Friday will usher in our first taste of fall with highs in the 70s and lows in the lower 50s.
The cold shot late next week will be short-lived however as the ridge will likely build back into the Mid-South and once again push temperatures well above normal for the 3rd week of September.