textproduct: Louisville

KEY MESSAGES

* Heat Advisory continues through Saturday afternoon. * Temperatures for remainder of today in the mid to upper 90s with heat index values over 100 and up to 107. Saturday will again be hot, with afternoon highs just a couple of degrees lower than today.

* Warm overnight temps tonight in the mid to upper 70s will provide little relief during the nighttime hours. Practice heat safety by remaining hydrated and limit time outdoors if possible.

* A weak cold front will increase the chance of isolated to scattered showers and storms Saturday afternoon and evening, ending our stretch of hot conditions across the region by the end of the weekend.

UPDATE

Issued at 1006 PM EDT Fri Sep 4 2026

At this hour, mostly clear skies are observed on nighttime microphysics satellite imagery, with a couple areas of lingering cu and high thin clouds noted. Temperatures are generally in the 80s at 02Z, though a few rural sites have already dropped into the upper 70s. For the rest of this evening and most of the overnight, precipitation chances are very low (<10%), as the mid- and upper- level ridge sit over the TN Valley. In areas which received substantial (>0.25") rainfall this afternoon, some patchy fog will be possible Saturday morning; however, given the spatial extent should be very isolated, not planning to add this to the grids at this time.

Over the next 12-18 hours, we'll have to watch nascent convection over the lower Great Lakes which is expected to drop to the southeast and strengthen in the presence of ample MLCAPE (3000+ J/kg). While the environment over our area is not nearly as favorable, some of this convection may be able to make it into our northern and northeastern zones by the mid-morning hours. To account for solutions like the 0Z HRRR which feature this wave of showers and storms, have added a chance PoP along and northeast of a Salem, IN to Stanford, KY line. However far southwest this morning convection makes it will have ramifications for temperatures and precipitation chances later in the day on Saturday, as new showers and storms will likely develop preferentially along the residual outflow from morning convection.

SHORT TERM /THROUGH SATURDAY NIGHT/

Issued at 356 PM EDT Fri Sep 4 2026

The hottest stretch of the year across the region continues this afternoon as broad upper-level ridging remains situated over the central and parts of the eastern CONUS. Louisville (SDF) recently hit 100 degrees for the first time since August 30, 2024, and the first September instance since September 3, 2011. In addition to the heat, isolated to widely scattered showers and storms have developed this afternoon, mainly for places south of I-64. The weak wind shear in place will limit the ability for more widespread development and stronger storms. The strongest storms could produce gustier winds, but the likelihood for any severe storms to develop remains very low.

Any showers and storms that do develop this afternoon will quickly dissipate after sunset, resulting in what should be a dry overnight across the region. A few clusters of showers and storms are likely to move over central Indiana and Ohio tonight, but should remain off to our north as they move through. Since an isolated shower cannot be completely ruled out, slight chance (<20%) POPs were included in the northern portions of the area. With the upper ridge still in place, overnight temperatures will remain warm, only dropping down to the mid 70s.

For Saturday, a surface "cold" front will move southward through the region, bringing a much-needed end to this heat wave. The front won't exit to our south until Saturday night, which will allow for temperatures in the mid to upper 90s in the afternoon. The area-wide Heat Advisory remains in effect until Saturday evening, with expected heat indices of 100-107.

The frontal boundary will also act as a forcing mechanism for more widespread showers and storms to develop tomorrow afternoon. While elevated moisture (PW ~1.7") and instability (1500-2000 J/kg SBCAPE), weaker wind shear (15-25 kt 0-6 km shear) will be a limiting factor to the intensity of these showers and storms. The SPC has placed the Bluegrass under a SLight Risk for severe weather Saturday, with damaging winds and very isolated hail being the primary concerns. Chances for showers and storms quickly decrease Saturday night as the front pushes southward and we lose daytime heating. While overnight temperatures won't be as warm, they will still be mild with lows in the upper 60s to low 70s.

LONG TERM /SUNDAY THROUGH FRIDAY/

Issued at 356 PM EDT Fri Sep 4 2026

Once the "cold" front departs out of the region, surface high pressure and drier air fills in. This will also mark the start of our much needed reprieve from the prolonged heat wave, with widespread afternoon highs in the mid to upper 80s and isolated low 90s forecast through the early parts of next week. Overnight lows will also be quite comfortable Sunday and Monday night, with temperatures in the 90s expected. In addition, this will also start a stretch of mostly dry conditions that is expected to last through midweek. When looking broadly at the upper-level pattern, the well amplified upper ridge over the central CONUS will begin to slowly break down beginning late Monday and shift eastward towards the Midwest and Ohio Valley. This will help shift the lower-evel flow back southward and allow warmer air to return, with highs in the low to mid 90s forecast Tuesday-Wednesday.

For the latter portions of the forecast period (late Wednesday and beyond), a more noticeable pattern shift could be in store fore the Ohio Valley. Guidance is picking up on a robust upper level low trekking towards the NE CONUS and Quebec by late week. As it does so, a southward extending cold front will pass through our region, providing the next opportunity for more widespread precipitation. The timing and progression of this system varies greatly across the deterministic and ensemble guidance,resulting in a wide variety of solutions. For example, when looking at the LREF maximum temperatures for Thursday-Saturday the 25-75th percentile spread is quite considerable (10-15 degree spread each day), ranging from the low 80s to upper 90s. As a result, our confidence in any particular outcome is very low, but will be something to monitor as time progresses.

AVIATION /00Z TAFS THROUGH 06Z SUNDAY/

Issued at 747 PM EDT Fri Sep 4 2026

VFR conditions are likely through the current forecast period, with a few low confidence scenarios that could impact operations. This evening, most of the showers and storms have dissipated, with dry conditions likely through Saturday afternoon. One outlier scenario (10-20% probability) features a gusty line of showers surging from the NE early tomorrow morning, mainly between 10-14Z. More than likely, this complex will remain away from forecast sites, but it's something to look out for.

Otherwise, tonight should feature light and variable winds, with winds increasing out of the W/NW during the mid-to-late morning hours Saturday. A few 15-20 kt gusts will be possible at SDF and LEX tomorrow afternoon, with winds veering toward the north by the end of the forecast period. Another mid-level cu deck should develop, with a better chance of showers and storms expected tomorrow afternoon as a cold front moves in from the north. May need to add more PROB30/TEMPO mentions for storms if confidence increases, with the main window for storms being 20-02Z Saturday afternoon/evening.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for KYZ023>043-045>049-053>057-061>067-070>078-081-082. IN...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for INZ076>079-083-084-089>092.