textproduct: Louisville

KEY MESSAGES

* Gradient wind gusts increase this afternoon and evening as a strong low pressure system approaches the Great Lakes. Non- thunderstorm wind gusts of 30-40 mph expected later today and into tonight.

* An approaching cold front is expected to bring a line of strong to severe thunderstorms into the area late tonight. Greatest severe threat is north of the Ohio River, but we could see strong to severe storms as far south as the WK/BG Pkwys overnight. Damaging winds are the main hazard possible, but can't rule out a tornado or hail risk either.

* The cold front stalls across the region, leading to additional potential for scattered strong to severe storms, excessive rainfall, and flash flooding across south-central KY on Thursday.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 351 AM EDT Wed Jun 17 2026

A busy weather pattern is in store over the next two days, with multiple hazards to discuss. We'll break them down piece by piece below.

===== Overview and Ensemble Analysis =====

An unseasonably strong low pressure system will deepen today as it tracks across the upper Midwest and into the Great Lakes region, with the possibility of the center of the low dropping to around 990 mb by early Thursday morning. This system will trail an extensive cold front through the Midwest, and a warm front eastward across the Great Lakes. Within the triple point region over north-central IL, there is a Moderate Risk for severe weather today. That trailing cold front will eventually arrive in our area by late tonight, and is expected to slow and nearly stall across KY tomorrow morning. This front placement and timing will be the focus for two rounds of severe weather potential across our area, with round 1 possibly after midnight tonight, and round 2 redeveloping along the front tomorrow afternoon.

Based off the ECMWF and NAEFS Ensemble Situational Awareness Tables (ESAT), there is significant signals aligning to show the rarity of a sfc low this strong for mid-June. Several parameters forecasted in the ensembles across the Ohio Valley are outside the Climate Forecast System Reanalysis (CFSR) database from 1979-2009, indicating this system to be quite remarkable. For example, the ECMWF MSLP forecasted is below all other MSLP values in the CFSR database for this time of year. Additionally, the 850mb jet is noted for either being strong enough that we see something similar less than 1 day every 10 years or will be outside the CFSR database as well. A LLJ of 50-60kts will pull an impressive moisture fetch into the region, with the IVT forecasts also exceeding the CFSR database. This translates to an impressive moisture fetch across the area, with PWATs expected to surge above 2 inches.

===== Strong Gradient Wind Gusts Expected =====

As the sfc low deepens throughout today, the sfc pressure gradient will strengthen, leading to increasing wind gusts this afternoon. Lapse rates will become quite steep this afternoon, supporting deeper mixing of the higher momentum aloft. Momentum transfer progs continue to support wind gusts of 30-35 mph later today, with isolated pockets of 35-40 mph possible. Debated this morning about the need for a wind advisory, but collaborated a SPS for now. This does not rule out the potential for an advisory being issued later today. Regardless, it will be unusually windy for mid-June. Wind gusts will continue into the overnight hours as well, both in and out of showers and storms.

These winds will be from the south today, ramping up WAA pattern and supporting temps reaching the upper 80s south of I-64 today.

===== Slight Risk for Severe Weather Late Tonight =====

A sfc cold front will trail across MO/IL/IN behind the deepening sfc low today, and will be the focus area for storms to fire up along and/or ahead the boundary later this afternoon and evening. While initial convection may be more discrete across MO/IL, hi-res guidance suggests convection will congeal into more of a linear component by this evening as the cold front approaches the I-70 corridor.

From there, we expect to see a line of strong to severe storms approach our southern IN counties late tonight, potentially after midnight, from the NNW. HREF mean 0-1km SRH increases as the front approaches tonight, with values near 300 m2/s2 possible as the LLJ significantly increases our shear profiles. While instability is not expected to be overly impressive, HREF SBCAPE values 750-1000 J/kg will be sufficient for thunderstorms.

The greatest severe risk will be across southern IN tonight, with severe potential expected to decrease as the line of storms slides south of the I-64 corridor. Damaging wind gusts are the primary concern, but there remains a tornado risk as well. However, as mentioned in the previous discussion, there is uncertainty around the tornado potential closer to the Ohio River and southward as the deep layer shear will be nearly parallel to the convective line/cold front. Given the amount of SRH and overall shear, can't rule it out, especially if there are any localized kinks in the convective line that can change the orientation of the shear vectors.

As for timing, generally expect severe storms between 1-3am EDT north of the Ohio River, and 4-7am EDT from the Ohio River to the WK/BG Pkwys. We'll likely see the line decrease in intensity as it moves south of the Pkwys tomorrow morning as the cold front slows its progression, which aligns well with the Marginal Risk.

===== Additional Slight Risk for Severe Weather Tomorrow =====

Showers and thunderstorms will likely be ongoing across central KY Thursday morning ahead of the cold front that nearly comes to a stop over the area. The location of the front by peak heating on Thursday will ultimately determine where the greatest shower and storm chances will be. The strongest moisture transport will be sliding east of the area, but still expect PWATs to be quite high. Along and to the south of the front, strong destabilization is expected to occur, with the HREF mean SBCAPE exceeding 2000 J/kg across south- central KY by Thursday afternoon. However, the LLJ will be moving off to the east, leading to weaker shear profiles, but still expect enough deep-layer shear for organized scattered convection to pose a damaging wind risk. Fortunately the shear profiles are more unidirectional, which will inhibit a tornado risk for Thursday.

===== Excessive Rainfall and Flash Flooding Potential =====

South-central KY will be on the northern periphery of a tropical airmass, with plentiful moisture, and southwesterly flow running parallel to the front to support backbuilding thunderstorms and training of heavy downpours. This set up could lead to some flash flooding concerns for Thursday afternoon and into Thursday night. The area with the greatest potential for hydro issues will be south of the WK/BG Pkwys.

LONG TERM /FRIDAY THROUGH TUESDAY/

Issued at 351 AM EDT Wed Jun 17 2026

===== Friday - Saturday=====

The cold front will be moving off to our southeast by Friday, leading to a return to drier weather as we head into the weekend. Cooler NW flow will filter into the region, and we'll gradually see cloud cover decrease from NW to SE through the day as sfc high pressure builds to the west. Highs are expected to be in the upper 70s to lower 80s.

Dry weather continues for Saturday as mid-level ridging and sfc high pressure move across the Midwest. Highs will be a touch warmer as we get into a deeper return flow as the center of the sfc high shifts east, so we'll likely see temps top out in the mid 80s for most.

===== Sunday - Early Next Week =====

An upper shortwave will transition across the central US on Sunday, and will drive a sfc low somewhere through the Ohio Valley. There remains some displacement of the sfc low track and timing, but global deterministic guidance and AI/ML probs indicate a chance for strong to severe storm potential for Sunday afternoon/evening. Still low confidence on timing and placement, but will be worth watching trends over the coming days. Another period of drier weather is favored behind this system for early next week, with temperatures remaining near or slightly below climatological norms.

AVIATION /06Z TAFS THROUGH 12Z THURSDAY/

Issued at 109 AM EDT Wed Jun 17 2026

VFR conditions are observed across the terminals this morning, with just a few mid-level clouds passing overhead. Main impact for this TAF period will be gusty non-thunderstorm winds ramping up this afternoon as a strong low pressure system tracks toward the Great Lakes. Our sfc winds will be from the south today, with sustained winds increasing to around 20kts, and gusts over 30kts expected for the afternoon and evening hours. Dry weather is forecast for the day, though a line of strong to severe thunderstorms will likely push southeastward through the area just after the 24-hour forecast period. However, this is highlighted with a PROB30 in the extended forecast at SDF. LLWS will also increase at LEX before any convection arrives later tonight.

LMK WATCHES/WARNINGS/ADVISORIES

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