500 Millibar Trap
Tuesday, September 1, 2026 · 6:39 PM
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A Heat Advisory is in effect for areas west of the Cumberland Plateau through at least Friday night. Major to extreme heat risk this week with heat index values in the triple digits. Wednesday and Thursday are expected to be the hottest days of the week. Very low rain chances through midweek. Stout ridge locked in! Five hundred millibar! Centered over Tennessee! Hot air trapped tight! Moist heat sealed down! Upper air flights confirm! No synoptic push! No front breaks through! Collaborate! Advisory spread! Lower River Valley! Heat index climbs! Past one hundred five! Burn the ground! FIVE HUNDRED MILLIBAR TRAP! FIVE HUNDRED MILLIBAR TRAP! FIVE HUNDRED MILLIBAR TRAP! FIVE HUNDRED MILLIBAR TRAP! Thursday strikes hard! Fifty percent shot! Nashville hits one hundred! No rain through midweek! Plateau on watch! Retrograde shift west! Plains move brief flow! Pattern sets back! Eighty percent! Ninety percent! Above average! No relief! Locked! In! Place! FIVE HUNDRED MILLIBAR TRAP! FIVE HUNDRED MILLIBAR TRAP! FIVE HUNDRED MILLIBAR TRAP! FIVE HUNDRED MILLIBAR TRAP! High chance! Late next week! Still locked! TRAP!
The forecast discussion
KEY MESSAGES
Updated at 632 PM CDT Tue Sep 1 2026
- A Heat Advisory is in effect for areas west of the Cumberland Plateau through at least Friday night.
- Major to extreme heat risk this week with heat index values in the triple digits.
Wednesday and Thursday are expected to be the hottest days of the week.
- Very low rain chances through midweek.
SHORT TERM
(Rest of today through Wednesday) Issued at 1153 AM CDT Tue Sep 1 2026
Middle TN is in the midst of an early fall heatwave, as evidenced by this morning's upper air flights.
A stout 596 dam ridge at 500 mb is centered over the TN Valley, trapping hot, moist air underneath it. These patterns are notoriously difficult to break up in the absence of a progressive synoptic pattern, much like we are seeing this week.
After collaborating with neighboring offices, a large Heat Advisory covers much of the Lower MS River and TN River Valleys starting at 11AM Wednesday.
Almost all of Middle TN (minus the Plateau) is included and can expect widespread heat indices above 105 degrees.
LONG TERM
(Wednesday Night through next Tuesday) Issued at 1153 AM CDT Tue Sep 1 2026
Expect progressively hotter conditions each day this week, especially on Thursday.
There is a medium chance (50%) Nashville's temperature could reach 100 degrees on Thursday afternoon.
As such, this Heat Advisory continues through Friday evening.
The Cumberland Plateau is currently not included but will keep an eye on heat index observations each day and make expansions as needed.
Long range ensemble forecasts suggest this upper level ridge will retrograde back over to the Central Plains some time over the weekend, providing us with a little relief in the form of northwest flow aloft.
This is only a brief intermission from oppressive heat, as this same ridging pattern sets right back in mid next week.
We're looking at a high chance (80-90%) of above average temperatures through the end of next week for all of Middle TN.