textproduct: Louisville

KEY MESSAGES

* Severe thunderstorms are likely from midday through this evening, with all severe hazards possible. Damaging straight-line winds are the main hazard, but a few tornadoes and large hail will be possible. Localized heavy rainfall may lead to flash flooding, especially east of I-65.

* Calm weather moves in with cooler than average highs for Wednesday through Friday this week.

* Rain chances return late week into the weekend with maximum temperatures returning to the 90s.

UPDATE

Issued at 341 PM EDT Tue Jul 21 2026

Semi-discrete supercells have now congealed into a squall line moving through south-central Indiana and into central Kentucky. Forecast updates reflect the timing of the system, which is closely mimicking the HRRR forecast. SPC mesoanalysis ahead of the squall line has very high CAPE (instability) amounts (SBCAPE upwards of 4000 J/KG, MLCAPE around 3000 J/KG), effective bulk shear between 40-50 KTS, PWs of greater than 2 (approaching climatological maximum for July), DCAPEs greater than 600 J/KG, and registering elevated numbers on several supercell/tornado parameters (supercell composite, effective layer STP, effective layer SRHs). Storms will continue to race toward the south/southeast direction into a ripe environment for storms to continue and/or strengthen for the next 4-6 hours.

SHORT TERM /THROUGH TONIGHT/

Issued at 145 PM EDT Tue Jul 21 2026

*** Today and Tonight ***

An upper level trough is beginning to drop south into the northern part of the Ohio Valley. An associated low pressure system over Ontario is draping a cold front SW through northern IL into the Central Plains. This front is expected to push through the forecast area today and tonight. Ahead of the line, PWATS are between 1.5" to 2" across the region (on the order of 75th to 99th percentile for late July). As storms start to move in this afternoon, PWATS could reach 2.5" (approaching climatological maximum for late July). Southern IN counties can expected for storms to start moving in early afternoon, with a some more discrete storms initially. As the afternoon progresses, a broken line of storms will beginning to develop over southern IN and move SW through KY.

All severe threats remain possible for this afternoon and evening. Gusty winds up to 70 MPH are expected with storms, along with a 1"- 2" hail threat. Isolated large hail is not out of the question, but has the greatest chance with discrete cellular storms rather than with the linear convection. A few isolated tornadoes are possible mainly east of I-65, but not off the table for the remaining of the forecast area. SBCAPE values are ranging from 2,000 - 4,000 J/kg across the area providing ample instability for the environment. Deep layer shear values of 30 - 40 kts are also expected to move in ahead of this line, adding to the threat of tornadoes. However, LCL heights are expected to remain marginal which would decrease that threat slightly. There is also a concern for flash flooding with the favorable PWAT environment. Storms will produce heavy rainfall leading to isolated flash flooding, along with any training storms through the evening hours. A flood watch has been issued for KY counties mainly east of I-65 that will run through late tonight.

LONG TERM /WEDNESDAY THROUGH TUESDAY/

Issued at 145 PM EDT Tue Jul 21 2026

*** Tomorrow - Monday Night ***

Behind the cold front, a surface high pressure will build into the Ohio Valley starting tomorrow. The upper level ridge that is currently in place over the southern Plains will continue to persist, leaving the Ohio Valley region in a northwesterly flow aloft. Tomorrow some gusty winds are possible through the day as a mid-level jet moves through. Maximum temperatures tomorrow are expected to be in the mid to low 80s tomorrow with the CAA behind the front. Temperatures will bounce back to the mid to upper 80s by Saturday.

The next chance for precip will be Friday as a shortwave trough moves east from the Central Plains. As we move into the late weekend early week, a couple frontal boundaries will move through the region. This will likely bring another round of rain showers for Sunday into Monday. Temperatures to start the week will be in the upper 80s and low 90s.

AVIATION /18Z TAFS THROUGH 00Z THURSDAY/

Issued at 145 PM EDT Tue Jul 21 2026

Convective activity over south central Indiana has initiated and is starting to move southeastward into the region. General arrival times are between 18Z and 19Z for south central Indiana terminals, 19Z and 20Z for Louisville area terminals, and pushing into central Kentucky (including Lexington, Bardstown, Elizabethtown areas) for 20Z to 21Z. Sites should expect a few hours (at least) of strong gusty winds and reduced visibilities from heavy downpours this evening. Hail is also a concern in these storms. Once storms pass, general wind direction will be out of the NW with some chances for patchy MVFR fog later tonight into tomorrow morning.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Heat Advisory until 7 PM CDT this evening for KYZ023-024-026- 027-061>063-070>076-081. Flood Watch until midnight EDT tonight for KYZ033. Flood Watch until 2 AM EDT /1 AM CDT/ Wednesday for KYZ034>043- 045>049-053>057-063>067-073>078-081-082. IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for INZ083-089.