textproduct: Louisville

KEY MESSAGES

* Heat Advisory has been extended into Saturday. * Friday afternoon temperatures in the mid to upper 90s with heat index values over 100 and up to 107. Saturday will see daytime highs in the mid to lower 90s and heat index values near or slightly above 100 to around 106.

* Warm overnight temps 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 late Friday into Saturday, ending our stretch of hot conditions across the region by the end of the weekend.

SHORT TERM /THROUGH SATURDAY NIGHT/

Issued at 327 AM EDT Fri Sep 4 2026

***HEAT CONTINUES - HEAT ADVISORY EXTENDED***

Heat Advisory continues through the end of the week and has been extended into Saturday. The upper-level ridging responsible for our ongoing heat wave will continue to keep things hot through today and into the start of the weekend, even as it starts to weaken and slowly shift westward. Confidence is high that afternoon temperatures will once again be in the upper 90s today with another shot of some locations seeing temperatures reach the 100 degree mark. Dew points are currently in the low 70s and will be there as we go into the start of the day, While some afternoon mixing is likely, this will lower dew points just a couple of degrees (68-70) but not enough to keep heat index values from getting back to around 102 to 107 later this afternoon.

Confidence has also increased that the ongoing heat will continue into the start of the weekend. The weak sfc boundary that is expected to bring to bring a brief period of relief from our on going heat wave is currently stretched across the Great Lakes from central WI across central MI, over Lake Erie into northwest PA and into western NY. This boundary is currently stalled and forecast guidance seems to be in general agreement that this boundary doesn't work into our area until late Saturday afternoon/evening. Giving the hot air mass currently in place a little extra time to linger over southern IN and central KY. That is why the decision was made to extend the current Heat Advisory through the day on Saturday.

Confidence is generally high that most locations across the CWA will see afternoon temperatures into the mid 90s for another consecutive day to start the weekend with heat index values over 100-105. Most notably for locations across southern KY and along and west of I-65. Confidence is a little lower (near or slightly above 50%) as you work further east and northeast towards Lexington and the Bluegrass. The potential limiting factors for the heat here is the approaching cold front from the northeast. Clouds from approaching convection and the development of pre-frontal convection Saturday afternoon would keep temperatures cooler than current guidance. It was the professional opinion of this forecaster that given the uncertainty of boundary arrival later Saturday as well as timing of prefrontal convective activity, it would be a lot easier to scale back and remove counties late Friday or early Saturday once we had higher confidence than to expire it too early.

***STORM CHANCES AND SEVERE THREAT***

While the current thinking is today will be mostly dry, hi-res CAMS continue to hint at isolated development later this afternoon, similar to what we saw yesterday. While forecast soundings show SBCAPE values between2000-2500 J/kg we continue to lack shear < 20kts as well as any strong forcing. After placing portions of our northern CWA in a Marginal Risk for severe weather today, SPC in their latest Day 1 outlook has removed most of our CWA from the Marginal with exception of our furthest east counties. Given the delay in frontal boundary arrival as well as the lack of forcing I agree with this as the though the last 24 hours was the threat of severe was very low.

In the SPC Day 2 convective outlook, they have put most of the CWA in a Marginal Risk (Level 1 of 5) with our far eastern counties, mainly those east of the I-75 corridor, in a Slight Risk (Level 2 of 5). As was mentioned in the previous discussion, while the boundary does represent better forcing for convective development, wind shear remains weak and limited. Main threat could be hail and gusty winds given the steeper lapse rates.

LONG TERM /SUNDAY THROUGH THURSDAY/

Issued at 327 AM EDT Fri Sep 4 2026

Cold front will have departed south by Sunday morning allowing for sfc high pressure to our northeast to build in over the region. This will give us a needed respite from the high heat we saw over the last week. This will cool temperatures into the upper 80s to near 90 with dew points in the low/mid 60s as the second half of the holiday weekend looks to be dry. Overnight lows will also be cooler with morning lows in the low/mid 60s by Monday morning.

This break from the heat is only brief as the upper ridge that retreated over the weekend builds back over the Ohio Valley by the middle of next week. While not as hot as the past week, highs will return to the low/mid 90s Tuesday through Thursday as well as increase moisture advection from the south. Could see heat index values near 100 by Wednesday but not for a prolonged length of time.

The end of the forecast period on Thursday becomes more uncertain as another pattern shift looks to take shape. Most deterministic and ensemble guidance picks up on a robust upper level low moving from central Canada towards the NE CONUS while a surface cold front passes over the Ohio Valley. The uncertainty lies in the timing and progression of these features, but it does appear that this could be the next chance for more appreciable precipitation across the region.

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/

Issued at 202 PM EDT Fri Sep 4 2026

VFR conditions will prevail through the TAF period. Isolated showers and storms have begun to develop this afternoon and will continue through the early evening hours. There is a storm currently near LEX that should remain off to the north and east over the next hour. While any new showers and storms could develop near the terminals this afternoon, confidence was too low to include in the TAF package. Winds this afternoon will be out of the WNW around 5-10 kt, though an occasional 10-15 kt gust cannot be ruled out. Winds will be relatively calm tonight before increasing back to the 5-10 kt range by late Saturday morning. Isolated to widely scattered showers and storms could begin to develop near the end of the TAF period, but confidence was also too low to include in the TAF.

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.