Rain chances delayed by tropical disturbance

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 ensemble member show solid support for both the rain chance around Tuesday of next week as well as for the cold shot late next week.

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.

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