textproduct: Louisville

KEY MESSAGES

* A cold front pushing into the area from the north tonight will bring numerous showers and thunderstorms. A few strong to severe storms will be possible, especially west of I-65. Damaging winds and localized flash flooding are the main threats with storms.

* Additional low (<20%) chances for showers and storms are possible through Saturday night, though most should remain dry after Thursday morning. Temperatures should be seasonable to slightly below normal through early next week.

UPDATE

Issued at 1045 PM EDT Wed Aug 19 2026

Convection has finally started to develop across southern MO this evening with cloud tops cooling rapidly as ascent spreads into that area. Across our region, partly cloudy skies were noted with temperatures in the lower 70s.

Heading into the overnight, latest CAMs continue to show convection developing across southern MO and into SE MO. While a low-level nocturnal inversion is expected to develop, model soundings upstream show a broad zone of elevated instability aloft. Flow aloft is expected to increase to around 40-45 kts due to the increase in the nocturnal low-level jet. Convective activity will gradually shift eastward into far southern IL and western KY after midnight and then likely move east-southeast across southern KY during the overnight hours. Moisture advection will transport rich moisture into southern KY with PWATs climbing to 1.8-2 inches. So the convection moving out of southern MO will likely train southeast and may bring excessive rainfall to portions of western and southern KY overnight. Mesoscale models suggest a swath of 1-3 inch rainfall across our southern/southwest sections. This area has missed out on the heavy rains over the last two weeks and has only seen about 2-20% of normal rainfall. So while FFG values are high, training storms dropping 2-4 inches in a short time can produce flash flooding. Based on the early 20/00Z guidance, we feel the best chances of flash flooding would be across our southwest/southern CWA. So we have hoisted a short term Flood Watch from Ohio County to Russell County and points south. Overall, not overly confident on the northern edge and eastern edges of the watch as convection is likely to weaken with eastward extent, especially east of the I-65 corridor.

SPC expanded the slight risk eastward overnight, mainly based on the potential elevated instability and possible cold pool generation which could focus a corridor of wind potential across western/southern KY. To us, the higher threat looks to remain south of the WK Parkway and west of I-65, with a diminishing threat as storms get east of I-65. Main hazards overnight will be torrential rainfall, the possibility of some damaging winds (isolated/scattered) and perhaps some marginal severe hail (very isolated) in some of the strongest cores. We do have the low-level jet providing some speed/directional shear, especially across western KY where an isolated spinup can't be ruled out.

Issued at 726 PM EDT Wed Aug 19 2026

Currently seeing partly to mostly sunny conditions early this evening across the forecast area with temperatures in the upper 70s to the lower 80s. Main forecast concern this evening will be watching convection develop out across southern MO and into SE MO late this evening with the convection pushing east into KY in the overnight period. Current forecast has too high of PoP this evening, so have gone in and backed off PoPs for the evening hours.

Into the overnight period, confidence in the convective evolution is still a work in progress. Instability has been on the increase across southern MO over the last several hours and we've seen some scattered convection start to develop. Looking through the last few runs of the CAMs, they have backed off the convective development a few hours and really develop things in the 20/01-03Z range. The recent CAM signals suggest that we'll have an instability gradient set up from southern MO into western/southern KY overnight and that a possible MCS will develop and trail down that gradient affecting southern Kentucky. Generally, we like that idea and have a bit more confidence with those trends. Forecast soundings do show an increasing PBL inversion setting up overnight which may lead to more of an elevated convective threat, rather than surface based. Though, given forecast lapse rates and expected shear, robust convection could linger into the overnight posing a wind and marginally severe hail threat in the strongest cores.

Heavy/torrential rainfall is likely with this possible MCS across southern KY. Expected moisture transport will likely allow PWATs to surge up to 2 inches or so. HREF QPF data shows a few swaths of 1- 3" of rainfall with a few localized 4-5" spots, especially where storms may train over the same areas (or have a boundary get laid out and have storms repeatedly roll along it). This area of KY has largely missed the heavier rainfall from last week, so FFG guidance is higher down that way. Nonetheless, some localized flash flooding will be possible. If a stronger signal appears in the 00Z guidance, a short term flood watch may be considered.

Further north, the convective evolution remains uncertain. Overall convective trends across southern IN and into the northern half of Kentucky have been trending downward, though a few CAM solutions have storms rolling through this region. Again, with PBL cooling, we're likely to see more elevated convection than surface based. Heavy rainfall, lightning and perhaps some gusty winds would be possible. We'll continue to monitor trends this evening and adjust the forecast as needed.

SHORT TERM /THROUGH FRIDAY/

Issued at 300 PM EDT Wed Aug 19 2026

This afternoon, a band of mainly mid-level clouds and light rain showers is attempting to move into central KY and southern IN from the southwest, struggling as it encounters drier air between the surface and 10k ft AGL. West of I-65, a few light rain showers have been able to reach the surface, though rain amounts have generally ranged from a trace to a few hundredths of an inch. East of I-65, less cloud cover has allowed temperatures to warm into the low-to- mid 80s, with upper 70s and low 80s observed along and west of I-65. For the remainder of the afternoon, ongoing showers and clouds to our west should gradually diminish, with the highest chances (20- 30%) for any additional rain showers expected across southern IN and west of I-65 in KY.

This evening into tonight, a 500 mb shortwave trough will eject from the Plains into the mid-Mississippi Valley, moving across the region during the early morning hours on Thursday. A sfc trough axis extending across the Ozarks will extend into the Ohio Valley this evening, serving as an effective cold frontal boundary, with low- level moisture pooling along and ahead of this boundary.

One of the main forecast questions for tonight is how much moisture return (and by extension, instability) will be able to extend to the east-northeast into our area. While short-range progs consistently show the greatest amounts of MLCAPE (2000+ J/kg) remaining across western KY and points southwest, some solutions do bring 1000-1500 J/kg of MLCAPE into our western and southwest counties late tonight into early Thursday morning. Helping to increase instability will be a 30-35 kt southwesterly jet at 850 mb, with around 15-25 kt of southwest flow extending down to 925 mb. With that being said, the warm/unstable sector with this system will be fairly narrow, and there is the potential that storms diving south across western KY/TN could cut off the warm sector and reduce the strong/severe storm potential. While instability is uncertain, deep-layer shear will likely be strong, especially for August, with around 40-45 kt of shear expected in the 0-6 km layer. That should allow any robust convection which develops to be well-organized into several bowing segments. These bowing segments would bring the main potential for strong to severe wind gusts, with the highest likelihood for severe winds expected across southern KY. While a spin-up tornado can't be completely ruled out if any segments orient perpendicular to the 0-3 km shear, elevated MLLCLs thanks to pre-existing dry air near the sfc should limit the overall threat.

Another potential hazard tonight into tomorrow morning would be heavy rainfall leading to localized flash flooding. Moisture advection ahead of the cold front should allow PWATs to surge to around 2" just ahead of the storms tonight. Additionally, any west- to-east moving lines of storms could leave a residual boundary resulting in training of showers and storms after the main severe threat diminishes. In both the 0Z and 12Z HREF 6-hr QPF data, there are a few swaths of 1-3" for areas especially along and west of I- 65, with hyper-localized amounts as high as 5" showing up. If any of these solutions with training convection and 3+" of rain occur, localized flash flooding will be possible.

With the upper wave that is providing a considerable amount of the forcing moving quickly through the region, the main timing for showers and storms should be fairly narrow between 10 PM tonight and 8 AM Thursday morning. By mid-to-late morning Thursday, the deeper moisture and stronger forcing will exit across the Appalachians, though the sfc cold front will be very slow in moving from north to south through the area. As a result, pooled low-level moisture should support continued low-level cloud cover through a good portion of Thursday, with isolated showers and thunderstorms possible in the afternoon and evening hours. These storms are unlikely to be severe, as weaker deep-layer wind shear and forcing will be much less supportive of organized convection. Highs tomorrow should be slightly below normal, with most areas reaching the low-to- mid 80s.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Issued at 300 PM EDT Wed Aug 19 2026

Thursday Night through Saturday Night...

The remnants of a sfc cold front should sink into southern KY and TN Thursday night as weak high pressure moves into the Midwest and Ohio Valley. While this should bring lower PWATs and deep layer moisture into the region from the north, near-sfc moisture levels are expected to remain elevated, with sfc dewpoints remaining in the upper 60s and low-to-mid 70s as we head into Friday. There may be just enough moisture across southern KY for additional rain chances Thursday night, but probabilities remain low (15-20%) at this time. If there is any clearing farther to the north, fog development would be favored Thursday night given light winds and a moist boundary layer, and there is already a modest signal on 12Z HREF guidance for fog Friday morning.

Friday into Saturday, the remnants of the front should dissipate and push to the south as troughing continues across eastern portions of the CONUS. Although the air mass should remain fairly muggy, limited forcing should keep most locations dry Friday into Friday night. A secondary upper shortwave is expected to drop across Ontario and into the northeast US Saturday into Saturday night, allowing a reinforcing cold front to approach the region from the north. While earlier model guidance suggested this system could bring a chance for showers and storms, potentially even a few strong storms, recent guidance has trended farther to the east with the mean trough axis positioning. As a result, better chances for showers and storms should remain to the northeast of the region Saturday into Saturday night, with only isolated chances for showers and storms expected across southern IN in the current forecast. Temperatures Friday into Saturday should be near to slightly below normals, with highs in the mid 80s and lows in the mid 60s.

Sunday through Early Next Week...

As the upper level pattern amplifies over the second half of the weekend, deepening troughing along the east coast should allow a cold front to push through the region Saturday night into Sunday. This front shouldn't bring much in the way of a cool down; instead, drier air will be the main feature of the post-frontal air mass, limiting precipitation chances for Sunday into early next week. LREF guidance shows ensemble mean PWAT values below climatological norms Sunday into Monday, with dewpoints in the upper 50s and low-to-mid 60s returning to the area.

As we head deeper into next week, a NW flow pattern should continue across the Ohio Valley, with ridging trying to extend into the Plains while troughing continues across the eastern seaboard. This pattern could bring the potential for transient systems to ride along the edge of the upper ridge, bringing a chance for showers and storms, though at this time, the strongest signal in guidance for these systems is to the southwest of the area.

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 146 AM EDT Thu Aug 20 2026

VFR conditions and light S-SW winds will continue ahead of a main cluster of storms moving through southern KY. These storms have proven to contain gusty winds, low visibilities and heavy downpours. BWG may experience this, with brief storm-induced MVFR-IFR conditions there. SDF-LEX may miss out on the worst of the storms, although PROB30s for less-impactful storms was included. When not in overnight storms, showers will be around with a continued SSW flow through sunrise. Showers and storms eventually move east away from all terminals in the morning. SDF may briefly drop to MVFR ceilings ahead of an approaching front as well. This front later Thursday afternoon will shift winds from out of the SW to out of the NNE later in the TAF period. VFR conditions will prevail Thursday afternoon.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Flood Watch until 7 AM CDT this morning for KYZ026-027-061>064- 070>078-081-082. IN...None.