textproduct: Louisville

KEY MESSAGES

* Scattered thunderstorms (30-50% coverage) are forecast southeast of the Western Kentucky and Bluegrass Parkways this evening. There is a level 1 of 5 (Marginal) risk for severe weather, with locally damaging winds the primary hazard.

* Unseasonably hot weather will continue over southern Kentucky today with heat indices in the mid to upper 90s.

* Milder weather will gradually overspread the area this week, with highs likely (70-80% chance) in the 70s north of an Owensboro to Berea line tomorrow, and area-wide Wednesday through Saturday.

SHORT TERM /THROUGH TUESDAY/

Issued at 133 AM EDT Mon Sep 21 2026

*** MILDER NORTH, STILL HOT WITH STORM CHANCES SOUTH TODAY ***

At 130am Monday morning, a quasistationary front, recognizable via a wind shift, was draped across roughly the Ohio River. Two perturbations along this front - one near the OH/WV border and another near the St. Louis Metro - have triggered scattered, sporadically severe, storms. The latter of these two storm complexes may threaten our area with convection after around 4am, and given the 25-35 kt deep layer shear coupled with 500-1000 J/kg MLCAPE forecast by the RAP there remains a nonzero risk for marginally severe wind despite a modest nocturnal inversion (25-50 J/kg MLCIN). CAMs suggest the greatest chances (30-40%) will be over southern Indiana, on the cool side of the front.

The front is forecast to sink slowly southward today, roughly bisecting the state from southwest-northeast by mid-afternoon. In its wake, northern portions of the area will be cloudy and have milder temperatures with highs in the low-mid 80s; meanwhile, conditions will stay unseasonably warm and humid south of the boundary where, despite poor mid level lapse rates around 6-6.5C/km (HREF mean), MLCAPE will climb to 1500-2500 J/kg. It'll take most of the day for surface heating to erode the cap, but scattered storms should fire in the warm sector by late afternoon or early evening, perhaps peaking in coverage right around sunset. HREF neighborhood probabilities for > 40 dBZ reflectivities (a proxy for moderate- heavy showers and thunderstorms) peak in the 30-50% range along and southeast of the Western Kentucky and Bluegrass Parkways during the 6-10pm timeframe. Given the aforementioned instability and modest shear (25-35 kt in the 0-6km layer), a few updrafts may become sufficiently organized to produce severe weather, with localized wet downburst-induced damaging winds the primary hazard given the high PWAT environment and steep low level lapse rates.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

Issued at 133 AM EDT Mon Sep 21 2026

*** MILDER WEATHER ARRIVES TUESDAY INTO WEDNESDAY ***

Global model guidance suggests our resident boundary will stall over the Lake Cumberland area tomorrow, perhaps allowing a rogue shower or two to graze our easternmost CWA. Elsewhere, conditions will likely (90% chance) remain dry, while northerly flow advects a cooler and less humid airmass into the region. Forecast highs range from the mid 70s over southern Indiana to the low-mid 80s across southern Kentucky. As the cold core of the upper level low swings overhead on Wednesday to bring weak synoptic-scale lift, we may wind up with a few diurnally-driven showers. In addition, Bufkit time- heights from the NAM depict a nearly saturated PBL and reduced visibilities, with a plan view also showing spotty QPF and 0% prob ice present both Tuesday and Wednesday nights - suggesting we could see some patchy drizzle, or at least a stratus deck.

Once this pesky low meanders off to the east on Thursday and ridging over the central US expands into our neck of the woods, we should see sunshine return, though the continued cool northerly flow will likely (60-80% chance) maintain highs in the 70s and overnight lows in the 50s - near normal for late September. Global models and their respective ensembles remain somewhat split on whether the cut off low over the Mid-atlantic/Northeast expands back into our area or we remain under the influence of the aforementioned ridge by the second half of the weekend, but the latter solution seems to be most popular at this time, as the NBM brings a 40-60% chance that high temperatures return to the 80s by Sunday and 70-90% chance by Monday.

AVIATION /12Z TAFS THROUGH 18Z TUESDAY/

Issued at 729 AM EDT Mon Sep 21 2026

Low MVFR stratus has crept into the HNB and SDF terminals early this morning, along with patchy fog which has recently overtaken LEX, but this should all break up within a few hours of sunrise with surface heating. In addition, a gravity wave north of a stationary front is resulting in a transient wind shift. Storms associated with this feature should generally stay north of the airfields but may bring a lightning strike or two to HNB the next hour or two.

Otherwise, main concern during the forecast period is the low chance of a pop-up storm at LEX, RGA, and BWG this afternoon along the front, for which prob30 groups remain. Near the end of the forecast period, GLAMP guidance suggests low ceilings and visibility reductions may accompany patchy drizzle, but confidence remains too low to add it during this forecast cycle.

LMK WATCHES/WARNINGS/ADVISORIES

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