Single Celled Microbursts
Monday, September 21, 2026 · 3:37 PM
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Today will still be hot, but heat index values should stay below one hundred five degrees. Low chance of severe weather this afternoon and evening across Middle Tennessee. Damaging winds are the primary threat. Major heat relief is on the way with temperatures falling to near normal levels by Wednesday. Eleven twelve A.M.! Central Daylight Time! The boundary snaps! Stationary front draped southwest to— Three twenty-nine P.M.! Peak heating aided by— One thousand Joules per kilogram! Downdraft convective available potential energy! Lines break off at— Forty to sixty percent probability! Convection allowing models paint— Sporadic coverage across— Sixty miles per hour downbursts! Single celled collapse at— Tuesday morning! Rain cools the region down below— Ninety degrees! No multicellular convection! Organized updrafts are— Lacking! Highs dropping on— NO MULTICELLULAR CONVECTION! UNORGANIZED UPDRAFTS COLLAPSING! ONE THOUSAND JOULES! ONE THOUSAND JOULES PER KILOGRAM! DOWNBURST! DOWNBURST! Falling through the column! Peak heating breaks the sky! Isolated! Violent! Single celled microbursts! Below ninety on Tuesday afternoon! Transition day! It breaks! It breaks!
The forecast discussion
KEY MESSAGES
Updated at 329 PM CDT Mon Sep 21 2026
- Today will still be hot, but heat index values should stay below 105 degrees.
- Low chance of severe weather this afternoon and evening across Middle TN. Damaging winds are the primary threat.
- Major heat relief is on the way with temperatures falling to near normal levels by Wednesday.
SHORT TERM
(Rest of today through Tuesday) Issued at 1112 AM CDT Mon Sep 21 2026
A stationary front that has been draped across the TN Valley for several days will finally get a move on today.
Expect a reinvigoration of convective activity along the front this afternoon and evening aided by peak heating.
CAMs are painting a pretty sporadic picture in terms of spatial coverage of storms today.
The boundary is oriented SW-NE across TN but storms will be pretty scattered across the state.
Forecast soundings suggest DCAPE on the order of 1000 J/kg, which is plenty to produce a few strong downbursts up to 60 MPH. Shear is pretty lacking, so don't expect any multicellular convection or organized updrafts.
They'll most likely be single celled microbursts like we see in the summertime.
The front won't make it through Middle TN until Tuesday, so PoPs are still in the 40-60% range through Tuesday morning.
The wonderful news is that things will FINALLY cool down for a meaningful period behind this front.
Tuesday is kind of our transition day as rain cools the region and the cooler, drier air behind the boundary starts to build in. Highs finally drop below 90 degrees on Tuesday afternoon for the first time in several weeks.
LONG TERM
(Tuesday Night through next Monday) Issued at 1112 AM CDT Mon Sep 21 2026
Wednesday begins our first true taste of fall.
Cool, dry air will send temperatures much closer to normal in the low 80s for the rest of the work week.
With high pressure in place to promote radiational cooling and resultant CAA, overnight lows continue to cool and will drop into the 50s by Saturday.
PoPs remain below 15% through the weekend but start to creep back up early next week.