textproduct: Louisville

KEY MESSAGES

* Unseasonably hot weather will continue for much of the area through at least Sunday. Barring any early day thunderstorms, heat indices will top out in the mid 90s to around 105 (highest southwest) each afternoon.

* There is a 30-50% chance (highest northeast) for showers and storms late this afternoon and evening, with slightly lower chances tomorrow. Locally damaging wind gusts and heavy rainfall may accompany the strongest storms.

* A weather system will bring higher rain chances (50-70%) Monday into Tuesday, followed by a cooldown to more seasonable temperatures (highs in the 70s, lows in the 50s) by the second half of week.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 310 AM EDT Sat Sep 19 2026

*** HOT WITH SCATTERED PM STORMS (SEVERE?) TODAY ***

Early Saturday morning, a quasistationary front, evident via a subtle dewpoint gradient, was situated over northern Kentucky and southern Indiana. In addition, a decaying outflow boundary left in the wake of last evening's storms has laid out near the Kentucky/Tennessee border. The former boundary is slated to lift northward as a warm front today, while confidence remains lower on whether the latter (outflow) boundary will fully mix out this afternoon or serve as a focus for a few storms. Convective allowing models (CAMs) are certainly more aggressive with thunderstorms along the warm front, but the ARW, HRRR, and FV3 try to pop a couple cells further south. Accordingly, we've maintained "slight chance" (i.e., 15-24%) probabilities of precipitation (PoPs) in the forecast across southern portions of the county warning area (CWA) while boosting them to 40-60% further northeast where confidence is higher in a loosely-organized mesoscale convective system (MCS). It is worth noting that most guidance is hitting areas just north our of local area (central IN into southwest OH) with the strongest convection, but given the weakly sheared (0-6km shear ~20-25 kt) environment and potential storm interaction(s) with the aforementioned outflow boundary confidence is low in placement. Wherever this potential MCS sets up, modest buoyancy (MLCAPE 1500-2500 J/kg), PWATs of 1.7-1.9 inches, and notable inverted V on forecast soundings suggests strong winds will be a concern, particularly with any bowing segments where wind production may be aided by a rear inflow jet (RIJ). CAM wind gust output supports this notion, with various CAMs spitting out splotches of 40-60 mph gusts, and a couple very isolated pockets of 70+ mph apparent in the ensemble max. SPC maintains a level 1 of 5 (marginal) risk for severe weather across areas east of a roughly French Lick, IN to E-town to Edmonton line, with damaging winds the primary hazard. Outside of storms it'll be another unseasonably hot one with afternoon highs solidly in the 90s for most of the area and dewpoints, pooling near the warm front, in the upper 60s to low 70s. This will result in yet another day of heat indices in the upper 90s to around 105, highest west of the marginal severe weather risk area where a Heat Advisory is in effect.

*** TOASTY AGAIN, LOWER CHANCE OF A STRAY STORM SUNDAY ***

The axis of the shortwave trough responsible for this evening's storms is slated to exit the local area early tomorrow morning, leaving subsidence in its wake. This should result in a drier planetary boundary layer (PBL) during the afternoon, when dewpoints may fall into the lower-mid 60s in many places. Still, it'll be hot with forecast high temperatures once again solidly in the 90s area wide - favoring yet one more day of Moderate to Major HeatRisk (highest southwest and in urban areas). In addition, we may once again see a stray shower or storm, with the highest chances in two separate areas: one along any remnant outflow boundary left in the wake of this evening's storms across the Bluegrass and another over southern Indiana/far northern Kentucky where a weak shortwave trough is forecast to provide lift during the late afternoon-evening. Shear is forecast to remain weak while instability is a bit lower compared to today, suggesting the risk for organized severe storms is low; even so, we can't rule out locally gusty winds in any collapsing taller core. SPC has areas near and north of the I-64 corridor outlooked in a level 1 of 5 (marginal) risk for severe weather.

LONG TERM /MONDAY THROUGH FRIDAY/

Issued at 310 AM EDT Sat Sep 19 2026

*** LESS HOT NORTH WITH A FEW STORMS MONDAY ***

The ridge will begin to break down early next work week as yet another shortwave trough crosses the area Monday evening. This could spark a few afternoon and evening storms, which may once again carry some risk for severe weather, though fortunately global models and their respective ensembles suggest some displacement between the best shear (north) and most optimal instability (south); the Low Resolution Ensemble Forecast (LREF) system only gives a 10-30% joint probability for > 1000 J/kg MUCAPE and > 30 kt 0-6km bulk shear across western/central Kentucky Monday afternoon (and this may be inflated due to timing differences among LREF members). Depending on timing of the trough, cold front, and associated storms, the area may see quite the gradient in temperatures during the afternoon, with some locations (most likely southern KY) topping out in the low- mid 90s and others in the upper 70s.

*** FEELING MORE LIKE FALL BY MID WEEK ***

Behind the front, more seasonable temperatures should overtake the region with highs in the 70s north and low to mid 80s south by Tuesday. Wednesday onward, raw (LREF) and calibrated (NBM) guidance agree temperatures are likely to peak each afternoon in the 70s and drop each night into the 50s - near to slightly below normal and certainly much more fall-like. This mild, dry weather is likely to persist at least through next weekend as the upper level trough slowly drifts from the Great Lakes into the Northeast, keeping our area under northerly flow/cool advection.

AVIATION /12Z TAFS THROUGH 18Z SUNDAY/

Issued at 708 AM EDT Sat Sep 19 2026

IFR clouds and patchy fog have developed over portions of central Kentucky and southern Indiana early Saturday morning, though the only airfield affected so far has been LEX, thanks to prolific mid- high clouds elsewhere. With sunrise soon, these low clouds and fog should quickly burn off and VFR conditions become predominant. Winds, light and fickle early this morning, should blow predominantly from the southwest at 5-8 kt during the day while VFR conditions prevail. However, scattered thunderstorms are forecast to develop over central/southern Indiana and may dive southeast into portions of north-central/northeast Kentucky during the evening hours. A PROB30 group remains at LEX and even SDF to account for this potential, which appears to be highest during the 22-01z timeframe. Can't rule out a spotty storm further south, but it is less likely. Like yesterday, thunderstorm outflows may bring a sharp switch to a northerly wind direction well ahead of associated precipitation.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for KYZ023>028-053-061>063-070>076. IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for INZ083-089.