textproduct: Louisville

KEY MESSAGES

* Waves of thunderstorms into tonight could generate severe weather, with damaging winds the primary hazard and a lower risk for large hail. The risk appears greatest (15-29%) near and west of I-65 during the evening.

* Repeated rounds of heavy rainfall in thunderstorms through this evening could result in flash flooding. There is a level 2 of 4 (slight) risk for excessive rainfall area-wide.

* Additional rounds of storms are possible (40-60% chance) both tomorrow and Friday, but confidence is low on severe weather and flooding potential each day.

* Outside of storms, heat indices are likely (50-80% chance) to surpass 100 degrees west of I-65 each afternoon through Thursday, and area-wide over the weekend.

UPDATE

Issued at 907 AM EDT Wed Aug 12 2026

Went ahead and expanded the Flood Watch along and north of I-64. Current N-S oriented convection continues to be fed by a weak but persistent low level jet. This feature is expected to weaken through the morning, and the overall convective intensity has been trending slowly downward. Still, training of moderate to briefly heavy showers and storms will continue for a while this morning, before at least some brief lull in convection may occur.

Focus then shifts upstream for an afternoon/evening rounds of storms approaching from the NW. This line of strong to severe storms combined with another round of training convection possible on the remnant outflow boundary overnight was enough to justify expanding and extending the Flood Watch through 12z. There are some concerns in the 12/00z HREF data for SW Indiana where localized rainfall amounts over 5" are showing up in max ensemble members and backed up by the PMM data.

SHORT TERM /THROUGH TONIGHT/

Issued at 309 AM EDT Wed Aug 12 2026

***** FLOODING POTENTIAL THROUGH THIS EVENING *****

At 3 am EDT, heavy thunderstorms were located over southeast and east-central Indiana, having formed at the interface of a 30-35 kt LLJ and a leftover boundary from evening storms. These should continue to drift southeast into southwest Ohio and northeast Kentucky while additional activity backbuilds to the north and northwest over central/northern Indiana. This suggests that the focus for heavy rainfall and flash flooding potential will be right along the northeast edge and just outside of our local area. However, a few of the 00z CAMs suggest additional backbuilding towards the west could bring repeated rounds of heavy thunderstorms into our eastern county warning area (CWA) during the mid morning/afternoon. In fact, the 00z HREF LPMM has pockets of over 3 inches of rainfall along and east of roughly the I-75 corridor by 18z/2pm; for this reason, and because heavy rainfall from last evening in parts of south- central/southeast Kentucky has lowered the flash flooding threshold (FFG) to less than 1.5 inches in 6 hours in spots, we've expanded the Flood Watch westward to include another row of counties. While the worst of this morning wave could stay off to the north and east, the CAMs seem to agree that the next mid-level shortwave arriving during the evening will spark additional storms that could prove efficient rainmakers (>1 in/hour rates).

***** SEVERE WEATHER RISK THIS EVENING *****

The CAMs seem to broadly agree that, once again, a complex of severe thunderstorms will develop over eastern Iowa/northern Illinois later this morning. Their solutions diverge, however, in what happens once that complex reaches Indiana. The latest (04z) HRRR, for example, has the line racing eastward across northern Indiana and northern Ohio, while the NAMNest and ARW, by contrast, suggest it will take a dive southward over east-central Illinois and southern Indiana during the afternoon. However, even the HRRR suggests the MCS will lay out an outflow boundary on which additional convection will fire during the late afternoon over central/southern Indiana, with that activity tracking southeast into our area during the evening hours. The main difference between the two solutions is timing, with the ARW and NAMNest being a little faster (late afternoon/early evening vs late evening). If this earlier outcome materializes, higher diurnal instability would suggest a greater severe wind risk, while the slower HRRR outcome would mean the risk will be lower, at least for areas east of I-65. Like yesterday, hodographs exhibit modest clockwise curvature in the lowest kilometer of the atmosphere, which may maintain a bit of a messy storm mode, with broken linear segments comprised of individual cells which could at times exhibit deviant motion towards the right; in addition, the resultant 100-200 m^2/s^2 0-1km SRH could favor a brief tornado with any individual cells, particularly right movers that realize the best low level shear. These will also be the ones to watch for locally severe hail, which, despite the warm and humid environment, was observed in our area yesterday in the most robust updrafts. SPC has the area outlooked in a level 2 of 5 (slight) risk for severe weather, with damaging winds the primary risk but a lower chance for hail and tornadoes.

LONG TERM /THURSDAY THROUGH TUESDAY/

Issued at 309 AM EDT Wed Aug 12 2026

***** STORM CHANCES WANE, HEAT BUILDS INTO THE WEEKEND *****

Global models and their ensembles agree that ridging will slowly build over the area into the weekend. One or more additional mid- level disturbances will offer thunderstorm chances Thursday into Friday, mainly east of I-65, but then the MCS corridor should shift to the northeast by Saturday. This will allow the heat to intensify across the area over the weekend, with triple digit heat indices, confined to areas mainly west of I-65 today and tomorrow, expanding east to encompass the entire area both Saturday and Sunday. In fact, there is a 60-90% (20-40%) chance HeatRisk reaches the major (extreme) category by Sunday afternoon - suggesting an increased risk for heat-related illness, especially among vulnerable populations including those without proper cooling.

A shortwave trough should flatten the ridge and drop a frontal boundary over the area sometime early next work week, potentially offering some relief from the heat for at least a portion of the area and serving as a trigger for showers and storms. It's too early to tell whether a severe weather risk may materialize with this activity, but the joint probability of > 25 kt 0-6km bulk shear and > 2000 J/kg MUCAPE from the LREF is less than 20%, which, at least at this point in time, suggests the risk should be relatively low. Given the richly moist and unstable airmass ahead of the trough and attendant front, heavy rain and localized microbursts in water-laden collapsing cores would seem to be the primary hazards (if any).

AVIATION /12Z TAFS THROUGH 18Z THURSDAY/

Issued at 719 AM EDT Wed Aug 12 2026

A complex of thunderstorms continues to progress southward across areas mainly near and east of the I-65 corridor, resulting in transient visibility and ceiling drops into the MVFR category. These storms should tend to weaken and break up later this morning, with VFR conditions predominant until the next wave of storms develops during the evening. Winds are shifting to a transient northeasterly direction with these storms, but should be predominantly out of the southwest throughout the forecast period.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Flood Watch through Thursday morning for KYZ025-029>043- 047>049-055>057-066-067. IN...Flood Watch through Thursday morning for INZ076>079-083-084- 089>092.