textproduct: Louisville

KEY MESSAGES

* An extended period of unseasonably hot and mostly dry weather is expected over the next 3-5 days. Take necessary heat precautions, including limiting time outdoors and remaining hydrated.

* Low (10-30%) rain chances return late in the week into the weekend, with a significant cooldown unlikely through Sunday.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 342 PM EDT Mon Sep 14 2026

This afternoon, 1026 mb sfc high pressure over southern Ontario is beginning to pull away from the Midwest and Ohio Valley as upper level ridging begins to amplify over the south central and southeast US. Low-level northeast flow has advected cooler and drier air across most of the area, though a notable N-S temperature/dewpoint gradient exists between the Ohio Valley and the TN Valley. For the rest of this afternoon into tonight, comfortable temperatures and mostly clear skies will continue, with light winds veering from the east to the southeast by Tuesday morning. Good radiational cooling conditions overnight should allow temperatures to fall into the mid- to-upper 50s across the KY Bluegrass, with stronger warm advection west of US 127 keeping temperatures milder in the low-to-mid 60s.

Amplification of the upper ridge tonight into tomorrow will support a significant warm-up for the day on Tuesday as the low-level flow veers from southeasterly to southwesterly. 1000-850 mb thicknesses will support high temperatures in the low-to-mid 90s, with the area of higher humidity also advecting back into the area. While heat index values should range from 95-105 across the area tomorrow, given that this is the start of an extended period of unusually hot weather for mid-September, folks should take appropriate precautions including remaining hydrated and limiting time outdoors.

A trough ejecting across the upper Midwest and into Canada tomorrow will bring a sfc cold front into the mid-Mississippi Valley by tomorrow evening. Ahead of this front, a plume of low-level theta-E advection will surge from the lower Miss. Valley up into IL/central IN, with our area on the southeastern edge of this higher moisture surge. While the best moisture and instability should remain to the northwest of the area, this forcing could be sufficient for the development of a stray shower or two west of I-65 and across southern IN. Poor mid-level lapse rates and broad subsidence should limit convective potential, so not expecting any thunderstorms tomorrow afternoon or evening.

Tuesday night into Wednesday morning, the sfc front north of the region will begin to stall as it encounters an increasingly unfavorable upper flow pattern. Convection along the front across central IL/IN will try to regenerate farther to the south along outflow, with some hi-res progs showing showers and possibly a storm reaching our southern IN counties early Wednesday morning. While confidence is low given convection diving headlong into a strengthening upper ridge, have added a slight chance (20%) PoP to the forecast north of the OH River Wednesday morning. Temperatures should be much milder, with lows remaining in the low-to-mid 70s.

LONG TERM /WEDNESDAY THROUGH MONDAY/

Issued at 342 PM EDT Mon Sep 14 2026

On Wednesday, upper level ridging over the southeast US is expected to intensify, with ensemble mean 500 mb height progs showing values around 600 dm over the TN Valley Wednesday afternoon. The subsidence associated with the growing heat dome should cause the sfc cold front to the north of the Ohio Valley to dissipate and lift back to the north, suppressing precipitation chances and reinforcing the unseasonably hot conditions. There is high confidence in unusually hot temperatures continuing into Thursday, as ECMWF Extreme Forecast Index values for high temperatures exceed 0.95, with a Shift of Tails around 1. Highs are expected to range from 93-97 across the area Wednesday and Thursday, with peak afternoon heat indices in the upper 90s and low 100s. Limited nighttime relief will exacerbate the effects of this late season heat surge, with lows only expected in the low-to-mid 70s through the week. As confidence in sustained hot temperatures continues later into the week, the heat advisory may need to be extended in time.

As we head into Friday and the weekend, the upper height anomalies over the southeast US will gradually break down from a combination of shortwave troughs riding across the northern US and a tropical wave slowly moving across the Gulf. However, recent runs of model guidance have trended toward persistence of the -PNA pattern with split flow across the western CONUS, which will limit the ability for troughing to dig across the eastern US. While the breakdown of the ridge should allow for a low (10-30%) chance of afternoon showers and storms to return, a substantial cooldown appears less likely through the weekend. With that being said, there is a notable uptick in spread in high temperatures over the weekend, possibly due to increased potential for clouds and precipitation to limit warming. A drier solution over the weekend would support continued highs in the mid-90s, potentially extending this heat wave.

AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 722 PM EDT Mon Sep 14 2026

VFR conditions will prevail through the TAF period. Light winds tonight will shift from the E to the SSW by midday Tuesday, increasing to around 7-10 kt during the afternoon hours. A light mid- level cu field is also expected to develop Tuesday afternoon, clearing out by the end of the TAF period.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Heat Advisory from noon EDT /11 AM CDT/ Tuesday to 8 PM EDT /7 PM CDT/ Wednesday for KYZ023>034-038-045-046-053-054- 061>065-070>077-081. IN...Heat Advisory from noon EDT /11 AM CDT/ Tuesday to 8 PM EDT /7 PM CDT/ Wednesday for INZ076>079-083-084-089>092.