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 20-40% chance for showers and storms late this afternoon and evening, with slightly higher chances tomorrow. Locally damaging wind gusts and heavy rainfall may accompany the strongest storms, especially tomorrow.

* A weather system will bring higher rain chances (50-60%) 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 SATURDAY NIGHT/

Issued at 256 AM EDT Fri Sep 18 2026

*** HOT WITH SCATTERED PM STORMS TODAY, TOMORROW ***

Early Friday morning, an expansive ridge of high pressure centered across the Southern Plains was maintaining dry and seasonably warm conditions over central Kentucky. Meanwhile, weaker associated subsidence further north over Indiana - nearer the periphery of the ridge - has allowed a few storms to fester along and south of a quasistationry boundary which is slated to drop southwestward across our area as a back door cool front tonight. Ahead of this front, afternoon temperatures are likely to, once again, climb well into the 90s near and west of I-65, and upper 80s to low 90s further east; combined with dewpoints in the mid 60s to low 70s, this will favor afternoon heat indices in the upper 90s to around 105 - again, highest west, where the Heat Advisory is in effect. A ribbon of moisture pooling immediately ahead of the front during the evening will foster a couple thousand J/kg MLCAPE, though forcing along it remains quite weak leading to uncertainty on whether any showers or storms will develop. We based precipitation chances off of the High Resolution Ensemble Forecast (HREF) and National Blend of Models (NBM), which give the area a 20-40% probability during the 5-10 pm timeframe. Since shear is weak, the chance of organized convection is low, but the moderate instability, high PWATs (1.8-2 inches), and steep low level lapse rates could favor both locally gusty winds to ~40 mph and briefly heavy rainfall (upwards of 1 inch/hour), along with cloud to ground lightning, under the tallest core(s). As is the case with the cells over Indiana early this morning, a few storms may fester into the overnight ours along and ahead of the front over central/southern portions of our area (a solution supported by the ARW, NAMNest, and FV3), but then increasing CIN and waning diurnally-driven instability should eventually overtake them.

Guidance generally agrees the front will slosh back northward into central Indiana/Ohio on Saturday, keeping the hot and humid airmass in place across our neck of the woods. However, the deterministic GFS, ECMWF, and NAM each depict a shortwave trough flattening the ridge Saturday evening/night, and CAMS suggest that ahead of this feature scattered thunderstorms will develop during the afternoon - perhaps limiting daytime highs. Given the uncertainty in when, where, and even if storms will form, confidence is low in whether and where a Heat Advisory may be needed for Saturday, though the highest chances are once again across areas near and west of the I- 65 corridor in Kentucky. We'll hold off for now on extending the Heat Advisory in time. Given another afternoon of modest instability (1500-2500 J/kg MLCAPE), and effective bulk shear climbing into a marginally supportive range (20-25 kt) for severe weather with the aforementioned trough, we may wind up with a severe storm or two with wind as the primary hazard; SPC has our area outlooked in a level 1 of 5 (marginal) risk for severe weather.

LONG TERM /SUNDAY THROUGH THURSDAY/

Issued at 256 AM EDT Fri Sep 18 2026

*** HOT START TO THE WEEK, THEN TURNING COOLER ***

The unseasonably hot weather will continue on Sunday as ridging restrengthens behind the Saturday night shortwave. In fact, subsidence in its wake should limit the chances for pop up afternoon storms, though this also suggests the airmass should be slightly less humid compared to today and tomorrow. Even so, high temperatures are slated to reach the mid 90s across parts of the area (highest southwest), which is contributing to 20-50% probabilities for Major HeatRisk.

At long last, a shift to more seasonable conditions is progged to follow the passage of a cool front accompanying a more potent upper level trough late Monday into Tuesday. Monday may remain quite toasty - particularly across southern Kentucky where deterministic NBM forecast highs are in the low-mid 90s - depending on when the front arrives, but by Tuesday a cooler and drier airmass should be pouring into the region from the north. In addition, the deterministic models (GFS, ECMWF, CMC) suggest this trough lingers over the Great Lakes/Northeast through at least late next week to perpetuate continued northwest flow/cool advection. The Low Resolution Ensemble Forecast (LREF) gives a 55-80% (70-85%) probability high temperatures don't climb out of the 70s by next Wednesday (Thursday) area-wide.

AVIATION /06Z TAFS THROUGH 12Z SATURDAY/

Issued at 128 AM EDT Fri Sep 18 2026

VFR conditions should be predominant throughout the forecast period. Light to calm winds mainly out of the southwest will switch around a northwesterly direction later this morning, then a more notable shift will occur behind a back door cool front during the evening. A couple storms may (20-40% chance) fire along and ahead of that front this afternoon-evening, so prob30 groups continue in the TAFs during the period of highest confidence.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for KYZ023>028-053-061>064-070>076-081. IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for INZ083-084-089.