textproduct: Louisville

KEY MESSAGES

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

* A Heat Advisory has been issued for portions of south central and west central KY, as well as southwest IN for heat indices of 100- 110 Tuesday afternoon.

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

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 323 PM EDT Mon Jul 20 2026

This Afternoon and Tonight...

Across the region this afternoon, scattered clouds continue as the stratus layer from this morning gradually mixes with drier air aloft. It is quite humid throughout the low-levels of the atmosphere, with sfc dewpoints generally in the mid-to-upper 70s across the area. Temperatures have warmed into the mid 80s, with heat index values generally in the mid-to-upper 90s at this hour. There have been a few showers which have developed across southern IN and north central KY over the past few hours, and a few pockets of agitated cu may lead to additional isolated showers and possibly a storm through early this evening. However, convective potential will be limited today by weak forcing and warm mid-level temperatures, with an upper-level ridge spreading from west to east across the Ohio Valley. Temperatures should reach the upper 80s to around 90 this afternoon before cooling this evening.

Tonight, an upper level shortwave is expected to swing around the edge of the mean trough, descending from the Dakotas toward Lake Erie by Tuesday morning. In association with this upper wave, a sfc low and cold front are expected to drop into the upper Midwest tonight, with pressure falling to the north of the Ohio Valley. While showers and storms will be ongoing to the north of our area tonight, the main impacts expected for central KY and southern IN through mid-morning Tuesday should be increasing southerly winds and increasing mid- and high clouds. There should be enough boundary layer mixing overnight to limit fog development, especially as clouds increase from the north.

Heat and Humidity Tuesday...

Ahead of the cold front and the storm potential tomorrow, one more day of hot and humid conditions are expected. The main uncertainty with the temperature forecast Tuesday will be with how quickly and how far to the southwest the first rounds of convection make it. In areas that remain storm-free, temperatures should warm into the upper 80s and low 90s, with heat indices surging above 100 degrees. In collaboration with offices to the south/west, a heat advisory was issued along and west of a line from Jasper, IN down to Burkesville, KY. Depending on how storm chances evolve in later guidance, this area may need to be expanded to the east.

Severe Storms Likely Tuesday and Tuesday Evening...

Tomorrow morning, a couple clusters of strong to severe storms are expected to approach the region from the northwest ahead of a cold front. Across our area, temperatures rising into the 80s with dewpoints in the upper 70s will support a highly unstable environment, with around 3500-4500 J/kg MLCAPE expected by peak heating Tuesday afternoon. Height falls with the descending upper trough over the Great Lakes should support a belt of strong west- northwest flow, especially by mid-Summer standards, with around 45- 50 kt expected by midday Tuesday. Model soundings show a decent amount of shear in the lowest few km early Tuesday, with winds gradually veering through the afternoon and evening as the sfc cold front approaches from the north. Additionally, if any discrete cells were able to develop, 0-1km SRH values exceeding 100 m2/s2 east of I- 65 would support an enhanced tornado potential, in line with the higher SPC tornado probabilities.

All in all, tomorrow still looks like a straight-line wind dominated severe risk. With model soundings showing limited capping in place, expect that storms may become fairly widespread and evolve into one or several bowing segments as deep-layer shear orients parallel to the cold front. While somewhat meager low-level lapse rates and ample boundary layer moisture will likely hamper the strength of any cold pools which can develop, would still expect stronger cores to produce instances of 60-70 mph winds. The tornado threat tomorrow should be maximized where (if) any discrete cells can develop, as well as along residual boundaries from antecedent waves of convection. Not to be discounted is the severe hail risk, which like the tornado potential, will exist primarily in any discrete cells or convective clusters and should decrease if updrafts begin to interfere as storms line out.

For the timing of the severe threat, there has been a shift with upstream convection potentially making it into the northeastern CWA as early as 9-10 AM EDT. From late morning through early evening Tuesday, would expect several waves of storms to move from north- northwest to south-southeast across the area, with storms expected to push into southern KY by 5-8 PM EDT/4-7 PM CDT. Although faster storm motions should limit residence time of any one round of storms, torrential rainfall rates and the potential for multiple waves of storms will support an increased threat for flash flooding. Along and east of I-65, widespread swaths of 1-2" of rain are likely, with isolated 3-5+" totals possible. If confidence increase in the location of heavier rainfall swaths, a short-fused flash flood watch may need to be issued subsequently. Storms should begin to push entirely out of the area by late evening Tuesday, or between 9 PM-12 AM EDT/8-11 PM CDT. A few lingering showers and storms may continue across southern KY into the early hours of Tuesday morning, but the severe threat should diminish significantly by midnight Wednesday.

LONG TERM /WEDNESDAY THROUGH MONDAY/

Issued at 323 PM EDT Mon Jul 20 2026

Wednesday through Friday...

The current model consensus has the surface cold front pushing through south central and southeastern KY during the morning hours on Wednesday, which may leave just enough forcing and low-level moisture in place for an isolated shower or two south of the WK/BG Parkways. Otherwise, the mid-to-late week period is expected to feature dry weather and pleasant temperatures across the Ohio Valley and into the mid South. Upper-level troughing continuing to dig across the eastern CONUS should help the sfc cold front push well to the south of the area as 1020+ mb sfc high pressure settles into the region from the north. The post-frontal air mass is expected to be quite refreshing given the recent prevalence of muggy weather, with ECMWF ensemble mean PW values falling below 1" (< 10th percentile of climo) Wednesday night into Thursday. Temperatures are also expected to be below normal Wednesday through Friday, with highs in the upper 70s and low-to-mid 80s with lows in the upper 50s and 60s.

Friday Night into the Weekend...

By the end of the week, the upper level pattern will become more zonal, though broad NW flow should continue across the Ohio Valley. A subtle upper shortwave is expected to eject across the northern US Rockies and into the Plains Thursday night into Friday before tracking toward our area Friday night. Ahead of this system, model guidance shows modest moisture return primarily into southern KY, with PW values creeping back above 1.50" later Friday into Saturday. While confidence is still low this far out, this could bring a return to isolated/scattered rain chances for the first part of the weekend. Behind this system, the broad upper ridge/heat dome across the western US is expected to nudge slightly to the east, with temperatures expected to trend back toward normal Sunday into early next week. Mostly dry conditions are expected late weekend as seasonable moisture and weak forcing are favored at this time.

AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 748 PM EDT Mon Jul 20 2026

Light SW winds and SCT-BKN high clouds are expected to begin this TAF period. We'll see increasing cirrus clouds spread southeast overnight from convection over Illinois. SW winds are forecast to steadily increase Tuesday morning ahead of a cold front pushing southeast across the Midwest.

At least one, possibly two, lines of storms are forecast to push southeast across the area from mid-morning Tuesday through early evening. Brief IFR conditions can be expected with TSRA. Breezy SW winds will become gusty Tuesday afternoon, with gusts to 20-25 kts. Some storms on Tuesday may be strong to severe, and will be capable of TSRA gusts in excess of 50 kts.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Air Quality Alert until midnight EDT tonight for KYZ029>031. Heat Advisory from 10 AM to 7 PM CDT Tuesday for KYZ023-024- 026-027-061>063-070>076-081. IN...Air Quality Alert until midnight EDT /11 PM CDT/ tonight for INZ076>079-083-084-089>092. Heat Advisory from 11 AM EDT /10 AM CDT/ to 8 PM EDT /7 PM CDT/ Tuesday for INZ083-089.