textproduct: Louisville

KEY MESSAGES

* Scattered (20-40% coverage) thunderstorms will pose a risk for cloud to ground lightning and heavy rainfall leading to localized flooding through around 9pm EDT this evening. Additional thunderstorms are forecast during the afternoon and evening Friday.

* Outside of storms, heat indices will peak in the 97-103 degree range each afternoon through Saturday. This will favor moderate heat risk, suggesting an increased chance for heat illness, especially among vulnerable populations.

* There is another chance (40-60%) for thunderstorms Saturday evening into early Sunday morning. Cloud to ground lightning, gusty winds, and locally heavy rainfall may accompany the strongest storms.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 256 PM EDT Thu Jul 16 2026

***** MUGGY, SCATTERED PM HEAVY STORMS THROUGH FRIDAY *****

Early Thursday afternoon, temperatures across central Kentucky and southern Indiana were in the upper 80s and dewpoints in the low to mid 70s - resulting in heat indices in the upper 90s. RAP mesoanalysis revealed 1500-3000 J/kg of MLCAPE, which, despite high pressure over the region, is already fueling a few thunderstorms this afternoon and evening as convective temperatures (around 85-88 degF) have been reached. The greatest coverage (30-40%) of showers and thunderstorms should be across areas near and west of the I-65 corridor where deep layer moisture is most pronounced and the remnants of a decaying mid- level low favor weak synoptic-scale lift. PWATs upwards of 1.9-2.0 inches in this area, "tall, skinny" CAPE profiles on forecast soundings, and a deep (>13 kft) warm cloud layer suggest these storms will be efficient rain-producers, and with less than 10 kt of deep layer shear they'll also be very slow- moving. Fortunately, this lack of shear will also limit the duration of individual storms, so, in the absence of training cells forming on preceding storms' outflow boundaries, the duration of heavy rainfall in any given area should be relatively short (<2 hours). Nonetheless, the ensemble max in both the High Resolution Ensemble Forecast (HREF) system and Rapid Ensemble Forecast System (REFS) have a handful of 1-hour precip bullseyes that exceed 2 inches, suggesting at least a low risk of localized flash flooding beneath the tallest cores; WPC's level 1 of 4 (marginal) risk for excessive rainfall seems appropriate.

Storms should dissipate between 8-10pm EDT this evening with the loss of diurnally-driven instability, then refire again early tomorrow afternoon when convective temperatures are once again reached. A disorganized mid level disturbance lifting into the area from the Deep South should spread the higher-moisture airmass that's west of I-65 today further east to encompass the entire county warning area (CWA), resulting in higher coverage of storms (50-65%) across the Bluegrass State. Given the environment will be similar to today, locally heavy rainfall and flash flooding are again concerns, and in addition the merging cells apparent in various convective allowing models (CAMS) suggests some potential for dropping precipitation-laden cores ("wet downbursts"), which can occasionally result in locally damaging winds. Like today, those storms should gradually diminish with waning instability after 8-9pm EDT. Outside of storms, conditions will remain seasonably muggy and uncomfortably warm during the afternoons both today and tomorrow, with daily peak heat indices near 100 degrees each day; accordingly, moderate heat risk suggests an increased chance of heat-related illness primarily among vulnerable populations.

LONG TERM /SATURDAY THROUGH THURSDAY/

Issued at 256 PM EDT Thu Jul 16 2026

***** FEW STORMS, SEVERE RISK(?) SATURDAY NIGHT *****

A seasonably potent upper level trough will dig southeastward across the Great Lakes and into New England Saturday into Sunday. The associated trailing cold front will eventually enter our area, but global model guidance suggests that's not going to happen until late Saturday night or early Sunday morning, by which time diurnal instability will be waning and optimal dynamics (forcing/shear) will be displaced well off towards the northeast. However, the NAMNest shows a pre-frontal trough triggering thunderstorms well ahead of the cold front during the mid-late afternoon timeframe. This solution would favor scattered to widespread (60-80% coverage) thunderstorms and a risk for severe weather Saturday afternoon- evening, while remaining guidance suggests we'll be dry during the evening and have only a low (20-40%) chance of a thunderstorm overnight into Sunday morning. The Storm Prediction Center (SPC) has our area outlooked in a level 1 of 5 (marginal) risk for severe weather, which seems reasonable given the uncertainty.

***** SEVERE RISK(?) TUESDAY, TURNING MILDER MID-WEEK *****

The front washes out over our area and high pressure builds in from the west on Sunday. This should favor drier weather, though we can't rule out (20-30% chance) a pop-up shower or storm along any remnant boundary during the afternoon and evening. Conditions will turn slightly less humid behind the front late Sunday into Monday, but then a stronger push of moisture and warmth will overspread the Ohio Valley ahead of a seasonably strong upper level low by Tuesday. The Low Resolution Ensemble Forecast (LREF) system depicts a 40-60% joint probability of 0-6km bulk wind shear > 30 kt and > 2000 J/kg MUCAPE Tuesday afternoon and evening, which suggests this system will bear watching for organized and potentially severe storms. In addition, several machine learning programs are advertising at least low (15%+) probabilities for severe weather across the local area during this time. However, lots can change between now and then, so stay tuned. Of higher confidence will be milder temperatures and lower humidity (dewpoints in the 60s) by Wednesday, when the National Blend of Models' (NBM's) 75th percentile for high temperatures are in the mid 80s. (This means there is a 75% probability that high temperatures will be lower than around 85 degrees.)

AVIATION /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 803 PM EDT Thu Jul 16 2026

Isolated SHRA/TSRA will gradually diminish over the next hour. Mainly dry conditions are forecast overnight, with scattered high clouds and very light winds. Fog appears likely at HNB given their higher crossover temperature and much lower dewpoint depression at this time. MVFR vsbys is likely at HNB between 06-12Z and tempo IFR conditions are possible (lower confidence).

Scattered convection will blossom over the region once again Friday afternoon and evening, so decided to introduce PROB30 groups for TSRA at all terminals.

LMK WATCHES/WARNINGS/ADVISORIES

KY...None. IN...None.