textproduct: Louisville

KEY MESSAGES

* A few storms are possible (20-40% chance) today, mainly north of I- 64 during the late morning. There is a low risk for severe weather with any storms this afternoon.

* Additional storms are possible (20-30% chance) across areas mainly east of a Salem, Indiana to Richmond, Kentucky line tomorrow afternoon and evening. Any storms that form could be severe with damaging winds and large hail.

* Outside of storms, heat indices are likely (60-80% chance) to surpass 100 degrees west of I-75 this afternoon. The heat and humidity peaks Saturday and Sunday, when HeatRisk is forecast to reach the Major category area-wide.

SHORT TERM /THROUGH TONIGHT/

Issued at 226 AM EDT Fri Aug 14 2026

***** WARM AND MUGGY WITH STORM CHANCES TODAY *****

Early Friday morning, ridging was present over the Deep South and Tennessee River Valley, while a shortwave disturbance was diving southeast across the Lower Great Lakes. At the juncture of these two features, optimal overlap of elevated instability and deep layer shear is sustaining robust and likely gravity-wave associated convection (GWAC) across portions of central/northern Illinois into central Indiana. Meanwhile, tranquil conditions persist over the local area, which remains largely stable in the wake of evening convection. A > 13 kft warm cloud layer, PWATs over 2 inches, and moisture transport into the activity to our north via a strengthening west-southwesterly LLJ suggests training, efficient rain producers which will carry and attendant flash flooding risk through sunrise. Fortunately, high resolution ensemble guidance from the HREF exhibits high confidence in the worst of this activity remaining just to the north of the local area. Though these ensembles are underdispersive, it's reassuring that the probability of more than 2 inches of rainfall, maximized (60-90%) near and just north of the I-74 corridor in Illinois and Indiana, drops off to less than 20% in Jefferson and Scott (Indiana) Counties. Still, several convective allowing models (CAMs) drop this activity into our local area after around 8am EDT, by which time it will be both weakening (due to a waning LLJ) and perhaps more progressive, particularly if a notable outflow can develop and push south. We increased rain chances in the forecast to 30-50% north of I-74 during the mid to late morning timeframe to account for this possibility.

The question then is whether a few storms may re-fire along any residual outflow boundary during the afternoon. The NAMNest, ARW, and a couple iterations of the HRRR fire a couple storms near/southeast of E-town between noon and 3 pm EDT, so we held on to 15-20% precip chances there, but those may need to be increased further if an outflow boundary does indeed push that far south across our area later this morning.

The prospect of early day storms and cloud cover, particularly across the northern half of the CWA, complicates the temperature forecast and has made it challenging to place a Heat Advisory for today. 14.00z HREF probabilities for afternoon heat indices greater than or equal to 105 degF (our Advisory threshold) are generally 50+% from Hancock to Marion to Cumberland Counties in Kentucky and points southwest; however, these "probabilities" as only as reliable as the models comprising them, and they've proven mercurial in this weakly forced environment so far this week. We're going to hold off until a bit later in the shift to reassess with some of the 06z guidance, but this is the area most likely to wind up with a Heat Advisory today.

LONG TERM /SATURDAY THROUGH THURSDAY/

Issued at 226 AM EDT Fri Aug 14 2026

***** HEAT SPREADS EAST INTO THE WEEKEND *****

In theory, our resident quasi-stationary front, which has served as a focus for convection in and northeast of the area all week, should lift far enough north to keep storms away both tomorrow and Sunday. However, I have trust issues with the more optimistic models at this point, having seen convective outflows sink further south and fuel more thunderstorms than guidance has suggested on multiple occasions. Consequently, I added some slight (15-24%) precipitation chances to the forecast tomorrow afternoon-evening northeast of a roughly Salem, IN to Richmond, KY line where the HRRR and FV3 fire a couple storms along an outflow boundary in an environment characterized by 3000+ J/kg MLCAPE and 20-30 kt 0-6km bulk shear. If we have storms, these parameters suggest they will be capable of producing severe weather, with both damaging winds and large hail concerns. Strong clockwise-curved hodographs suggest we'll need to keep one eye on the tornado potential with individual cells, but LCLs (1000-1400m) appear to be on the high side for tornadoes and the better shear is between 1 and 3km (vs 0-1km); in addition, the hodograph bends back in on itself throughout the rest of the cloud layer (up to around 13kft), suggesting poor ventilation may limit updraft strength and longevity.

The bigger story this weekend will be heat and humidity, which outside of storms will become oppressive at times. Uncertainty in the extent of potential convective activity has precluded a Heat Advisory for Saturday and Sunday at this time, but one will almost certainly be needed for most, if not all, of the county warning area both days as afternoon temperatures reach the mid 90s and dewpoints hover in the mid to locally upper 70s - pushing heat indices to 105- 110. In addition, warm overnight low temperatures in the mid to upper 70s will offer little relief to those without proper cooling, which pushes HeatRisk into the Major Category for most of the area both Saturday and Sunday.

***** LESS HOT, MORE STORMY TO KICK OFF NEXt WORK WEEK *****

A shortwave trough looks to flatten the ridge late Sunday into Monday, bringing better (40-70%) chances for storms as early as Sunday night, and perhaps offering at least limited relief from the oppressive heat and humidity Monday into Tuesday. WPC Cluster analysis suggests that, by midweek, the highest source of uncertainty among long range ensembles (given by PC1 for EOF1) is in the east-west placement of h5 ridging building over the central US and hence: whether our area sees (outcome 1) oppressive heat return or (outcome 2) remains far enough northeast of the ridge to instead see more seasonable temperatures and waves of "ridge-riding" thunderstorms. About 50% of models favor each scenario.

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 707 AM EDT Fri Aug 14 2026

An outflow boundary from decaying storms dropping south out of Indiana may spark a few additional showers at HNB and SDF, but otherwise dry conditions are likely (80%) chance throughout the day. A pop up storm can't be ruled out during the afternoon, but the chance was too low to warrant a prob30 group at this juncture. Winds will blow predominantly out of the southwest around 5-8 kt mid morning through the afternoon.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Heat Advisory from noon EDT /11 AM CDT/ today to 9 PM EDT /8 PM CDT/ this evening for KYZ023-024-026>028-053-054- 061>065-070>077-081. IN...None.