textproduct: Louisville

KEY MESSAGES

* Mainly dry today across much of central Kentucky. Scattered showers and thunderstorms are likely north of I-64 late this afternoon and evening.

* Shower and storm chances will continue tonight through Sunday morning. Excessive rainfall is likely across southern Indiana and portions of northern Kentucky. A Flood Watch is now in effect for portions of southern Indiana and the Louisville Metro.

* Summer heat and humidity will build across the region next work week, with triple digit heat indices likely (60-80% chance) west of I-65 on Monday and area-wide by Tuesday. This will pose a risk for heat-related illness, especially among vulnerable populations.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 414 AM EDT Thu Jun 25 2026

Today - Tonight...

Today starts off dry and partly cloudy. SCT cirrus is in the process of clearing west to east, while SCT mid-level clouds develop southeast over the Lower OH Valley. Through tonight, ridging aloft will be centered over Mexico and Texas. A progressive, mostly zonal flow will persist over the central and eastern CONUS. A primary upper level trough and weakening sfc low will develop eastward across the Great Lakes, dragging a cold front into central and southern portions of IL/IN/OH.

Modest SW low-level flow will help pool moisture along and north of I-64 this afternoon and evening, just ahead of the approaching boundary. Synoptic scale ascent is limited to low-level moisture convergence along the cold front. Southern IN and central KY will be positioned along the far southern fringe of the 40-60 kt mid-level westerlies, so any convection that develops later today will be loosely organized at best.

The latest 00Z CAMs point to scattered convection developing south into southern IN and northern KY late this afternoon and evening, mainly after 20-21Z. These storms should continue through 03-04Z tonight before weakening due to waning instability. The overall severe weather risk is muted by a lack of stronger forcing and deep- layer shear. However, locally heavy rainfall will be possible north of I-64. PW values are forecast to increase to around 1.8 inches by this evening, and HREF LPMM QPF hints at a swath of 1-2 inches north of I-64 through 12Z Fri. Localized 2-3+ inch amounts cannot be ruled out over SW Indiana. Given antecedent conditions and the potential for training convection into the weekend, think the confidence is high enough to issue a Flood Watch for most of southern IN plus the Louisville Metro. Depending on this evening's rains and future model data, this watch may be expanded slightly heading into the weekend.

Friday - Friday Night...

A mid-level shortwave trough and stronger sfc low are forecast to develop ENE along the stalled frontal boundary. This wave will bring notably stronger forcing and moisture transport to the region Friday and Friday night. A 30-40 kt LLJ will stream in Friday afternoon into the overnight. The deep-layer WSW flow and moisture axis being largely parallel to a quasi-stationary boundary continues to increase concern for flooding in the Lower OH Valley. HREF mean PW values increase to around 2 inches Friday. A high freezing level and tall, skinny CAPE profile will support highly efficient rainfall.

Scattered showers and storms will be possible throughout most of Friday into Friday night. A few storms could become strong in a modest CAPE-shear environment. The strengthening southwesterly LLJ will help produce at least a small risk (SPC 2% TOR risk) for a tornado. Locally strong wind gusts would be the other main severe weather hazard with any strong storms. However, the main concern overall is flooding. The setup appears especially conducive to training along the deep moisture axis, which may produce locally significant flooding.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Issued at 414 AM EDT Thu Jun 25 2026

At the start of the period, a quasistationary frontal boundary will stretch across central IL to central OH. We may still have enough of a westerly LLJ at this time to support a few lingering showers or storms, though the shortwave trough responsible for all of the rain on Friday should be shifting east and out of the area by this time. With the seasonably humid airmass in place and cloud cover, we'll start the day with temperatures in the low 70s, and, with any breaks of sunshine, warm into the mid-upper 80s during the afternoon. This will result in a couple thousand J/kg SBCAPE which is supportive of thunderstorms, however there remains no clear evidence of a strong forcing mechanism in the deterministic guidance. Perhaps an outflow boundary from early morning activity will initiate afternoon updrafts, or perhaps, as the RRFS suggests, the convective temperature will be reached and storms will fire in the absence of forcing altogether. Given this uncertainty, whether a portion of the area will see thunderstorms during the day on Saturday remains unclear. However, with the GEFS/EPS ensemble means holding PWATs around 1.8-2.0 inches, a deep (>12 kft) warm cloud layer, and slow storm motions stemming from weak (20-25 kt) deep layer shear, any storms that develop will pose a risk for locally heavy rainfall - and this could cause flooding, especially in any areas that received heavy rainfall on Friday; given the low confidence in even getting thunderstorms Saturday afternoon, we'll message this as a low- confidence, but potentially high-impact, scenario at this time.

Global and deterministic models are in agreement that a ridge of high pressure will build across the southern US on Saturday, and expand northward into the Midwest/Great Lakes Regions through next week. Saturday night into early Sunday, it appears we'll have one more pesky shortwave diving southeast through the area along the expanding ridge's periphery, potentially (40-60% chance) sparking another wave of showers and storms. Then as subsidence associated with the ridge builds in, conditions should turn drier and temperatures climb a few degrees each day early to mid next work week. After the recent heavy rains in north central KY and southern IN, evapotranspiration (ET) should foster a planetary boundary layer (PBL) moisture flux that restrains the heat but simultaneously increases humidity, while areas further south and west see slightly warmer temperatures and less suffocating humidity. In both locations, this combination should favor afternoon (overnight) heat indices in the triple digits (mid-upper 70s); confidence is increasing that a Heat Advisory will be needed at some point next week, with the highest chances (40-60%) both Wednesday and Thursday.

AVIATION /12Z TAFS THROUGH 18Z FRIDAY/

Issued at 707 AM EDT Thu Jun 25 2026

Lingering SHRA/TSRA over the Wabash Valley will diminish as they attempt to push into far southern IN mid-morning. Prevailing VFR conditions still appear likely this morning into early afternoon. Winds will gradually increase to 5-10 kts out of the SW by mid to late morning.

SCT TSRA are forecast to develop south across portions of southern IN and northern KY late this afternoon and evening, mainly after 20- 21Z. TSRA could bring brief MVFR/IFR conditions at HNB and SDF. LEX could also see a brief shower or storm this evening, but the window of opportunity will be shorter at that terminal.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Flood Watch from 5 PM EDT this afternoon through Saturday morning for KYZ030. IN...Flood Watch from 5 PM EDT /4 PM CDT/ this afternoon through Saturday morning for INZ076-077-083-084-089>092.