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 (50-70%) 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 306 PM EDT Fri Sep 18 2026

Remnant outflow from this morning's convection over the NE CWA has now settled NW to SE along a line from Campbellsburg, IN down through the Louisville Metro, and southeastward through Nicholasville, KY. This feature is going to be the focus for renewed convection this afternoon and early evening as some moderate instability is now pooling along it. Just recently had convective initiation across southern Washington county Indiana, and expect that initiation could occur anywhere along this feature over the next 1 to 2 hours. Elsewhere, we could pop a few very isolated showers or storms once convective temps in the mid 90s are reached, however it is also worth noting that areas SW are closer to the upper ridge center where mid level subsidence will be more notable. So, mainly have isolated to widely scattered (20-40%) Pops for areas in and around the aforementioned boundary through around sunset or a little after. The overall environment lacks deep layer shear despite the moderate instability, so expect only pulse storm modes with brief heavy rainfall, CG lightning, and perhaps some gusts up around 40 mph with the strongest cells. Anything above that would be very isolated in nature.

Outside of the shower and storm threat this afternoon and early evening, the other issue continues to be the Heat Advisory across the SW half of the CWA. Here, the remnant outflow and convective cloud cover will not have an impact so temperatures have been allowed to once again rise into the mid 90s coupled with lower 70s dew points. No changes planned to the current Heat Advisory headline, except that we have extended a similar portion of it into Saturday. A few counties on the far NE and E fringes of today's advisory have been trimmed for tomorrow. Expect peak afternoon heat indices once again up to 105F.

In addition to the heat and humidity for tomorrow, SPC has included a Marginal Risk (level 1/5) for a very localized damaging wind threat. The aforementioned boundary will stay stalled over our area until tomorrow when it begins to push back to the ENE as a weak warm front. Given some moderate instability between 1500-2000 J/KG of ML CAPE expected, this should be enough of a trigger for scattered afternoon and evening convection once again. Overall deep layer shear will still be quite weak with pulse storm modes anticipated again. Given the slightly stronger instability tomorrow, suppose a few stronger pulse storms are possible warranting the 5% Damaging Wind prob from SPC.

LONG TERM /SUNDAY THROUGH FRIDAY/

Issued at 306 PM EDT Fri Sep 18 2026

Sunday - Monday...

The upper ridge breaks down a bit across the southern CONUS to end the weekend. As a result, a belt of slightly stronger westerlies sinks a bit southward from the Corn Belt through the mid Atlantic. A surface front will also accompany this southward shift as it settles into the Ohio River Valley region by Monday morning.

We'll still be hot and muggy on Sunday ahead of the boundary as it approaches, however it looks like it will be displaced to the north enough to not be a factor on Sunday. In addition, we'll likely still have enough influence from the weakening upper ridge to keep the area dry. Given Max Ts and the low and mid 90s and dew points in the 65 to 70 degree range, we'll still see max heat indices in the 95 to 100 F range on Sunday.

By Monday, the front does sink into the area with cooler temperatures in the low and mid 80s across our northern CWA, but still in the upper 80s and low 90s across southern KY. We'll also have scattered afternoon and evening showers and storms triggered by both the frontal boundary and perhaps some subtle embedded shortwave activity passing through the flow.

Tuesday - Wednesday...

The real cool down sets in through mid week as a notable shortwave rotates through the lower Great Lakes and Ohio River Valley region. The aforementioned surface front will push south of the area with much cooler temperatures in the 75-80 degree range across southern IN and northern KY, and in the 80-85 degree range across southern KY. We'll also have pretty good coverage of showers and storms (up to 70% east of I-65) on Tuesday ahead of the shortwave trough axis. By Wednesday, the shortwave trough axis will be slowly pushing east of the area, but will likely be still carrying pops across our eastern CWA, with better chances for drier weather across the western CWA. Temps will even be cooler by Wednesday with low and mid 70s north, and highs near 80 across southern KY.

Thursday - Friday...

Good chance that we get back into dry NW flow aloft for late week. This should be a drier pattern, with temperatures mostly in the mid and upper 70s. It should be noted that the mid to late week "cool down" really just ends up being temperatures back close to normal for this time of year, maybe slightly below on a couple of the days.

AVIATION /00Z TAFS THROUGH 06Z SUNDAY/

Issued at 725 PM EDT Fri Sep 18 2026

Active thunderstorms should fully dissipate around 02z. A chance remains in the TAF cycle for thunderstorms through then, mostly a danger of gusty winds via storm outflows and lightning as the primary risk-drivers for LEX/RGA/SDF/HNB. VFR conditions will prevail throughout the cycle, although fog is expected at HNB/LEX/RGA and possible at SDF in the early morning hours. Outside of a stray outflow, winds are expected to slowly turn from northeasterly to southeasterly throughout the period. A lower cloud deck is expected as the precip remnants and fog mix out overnight, but should not be a full CIG. Tomorrow afternoon brings another chance for storms and a turn towards SWerly winds.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for KYZ023>028-053-061>063-070>076. Heat Advisory until 7 PM CDT this evening for KYZ064-081. IN...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for INZ083- 089. Heat Advisory until 8 PM EDT this evening for INZ084.