600 Decameters High
Wednesday, September 16, 2026 · 11:59 AM
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Very hot and humid conditions with triple digit heat indices to continue this week. A Heat Advisory is in effect through Saturday for most of Middle Tennessee. Not as hot early to mid next week, but overall temperatures will stay above-normal for the foreseeable future. Low rain chances mainly for the Plateau this weekend. Low to medium rain chances area-wide early to mid next week. Deep layer pressure! Locking down the state! Five hundred millibar heights rising! Six hundred decameters! Record high at B N A! Ninety-nine degrees today! Tying two thousand nineteen! Eight hundred fifty millibar sounding! Air remains stagnant! No rain to save us! The ridge will not yield! STAGNANT DOME! TRIPLE DIGITS! HEAT ADVISORY! 600 DECAMETERS HIGH! Appalachian periphery! Tropospheric moisture wraps around! Isolated diurnal convection! Cumberland Plateau target zone! Surface troff approaches late! Above normal forever! Bark! Bark! Clipped breath! Sultry sky! Burn! STAGNANT DOME! TRIPLE DIGITS! HEAT ADVISORY! 600 DECAMETERS HIGH! 600 decameters high! Foreseeable future! Burn!
The forecast discussion
NEW SHORT TERM, LONG TERM
KEY MESSAGES
Updated at 1155 AM CDT Wed Sep 16 2026
- Very hot and humid conditions with triple digit heat indices to continue this week.
A Heat Advisory is in effect through Saturday for most of Middle Tennessee.
- Not as hot early to mid next week, but overall temperatures will stay above-normal for the foreseeable future.
- Low rain chances mainly for the Plateau this weekend.
Low to medium rain chances area-wide early to mid next week.
SHORT TERM
(Rest of today through Thursday) Issued at 1155 AM CDT Wed Sep 16 2026
RAP mesoanalysis shows the deep-layer ridge centered right over Tennessee currently, with 500 mb heights near 600 decameters.
Boundary layer winds remain southerly to southwesterly and we've already got decent mixing outside with a few wind gusts observed.
We'll be on our way to high temperatures in the mid to upper 90s west of the Plateau this afternoon.
Some spots could hit 100 degrees again.
BNA's latest forecast high of 99 would tie the record set in 2019. Looking at observations so far this morning show we are trending 2-3 degrees behind this time yesterday with a slight cooling of 850 mb temperatures evident on the morning sounding, so perhaps we stay just under 100 degrees at BNA today, we'll see.
Nonetheless, near record breaking temperatures combining with humid air is leading to continuation of excessive heat that will persist through the short-term with little to no rain chances.
Forecast/NBM temperatures for tomorrow are nearly identical of that today.
LONG TERM
(Thursday Night through next Wednesday) Issued at 1155 AM CDT Wed Sep 16 2026
The center of the anomalous ridge will start to shift a little to our west on Friday as it interacts with an upper-low moving west toward Florida.
By then better tropospheric moisture is expected to wrap around into the eastern periphery of the ridge, basically down through the Appalachians.
This will support isolated diurnal convection Friday into the weekend, mainly focused near and across the Cumberland Plateau.
Forecast details for next week are a little less certain in some ways, but medium-range guidance/ensembles suggest a decrease in temperatures and increase in rain/storm chances as we are more influenced by systems passing to our north with a weaker ridge across the Southeast.
Associated presence of a front/surface trough will also play a role in encouraging better convective coverage early to mid week.
Either way, the trend is an improvement as conditions don't look as hot, but remain above- normal temperature wise.