321 FXUS63 KLMK 291912 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 312 PM EDT Mon Jun 29 2026 .KEY MESSAGES... * Hot and humid today with afternoon highs in the low to mid 90s and peak afternoon heat indices in the 100 to 115 degree range. An Extreme Heat Warning is now in effect through Thursday. * A strong ridge of high pressure over the region will bring the hottest temperatures so far this year. The heat will peak Tuesday through Thursday, with afternoon highs in the mid 90s and peak index values of 100 to 115F. * Hot and humid for the Fourth of July holiday weekend, with isolated to scattered storms possible in the afternoon and evening. Localized flash flooding and/or localized gusty winds will be possible each afternoon and evening with any slow moving storm. && .SHORT TERM /THROUGH TONIGHT/... Issued at 310 PM EDT Mon Jun 29 2026 The well-advertised anomalous upper ridge builds in and centers over our region through tomorrow. Dry forecast during this time with strong subsidence inversion showing up on area forecast soundings. The main story will be the heat and humidity with temps expected in the low and mid 90s combined with dew points in the 70s. Areawide max heat indices are expected to range in the 100 to 115F range each afternoon and evening, with little relief at night as temperatures only into the mid and upper 70s for most. Given the prolonged nature of the heat and humidity, a busy outdoor week leading up to the holiday, recent flood impacts and recovery ongoing decided to upgrade the entire area to an Extreme Heat Warning in coordination with surrounding offices. Do think temperatures will struggle a bit with the recent heavy rainfall, and available low level moisture contributing to sct-bkn cu fields each afternoon/evening, however any decrease in max Ts will likely be offset by higher dew points so it may end up being a wash on peak afternoon heat indices. Not much else to speak about in the short term other than perhaps some patchy fog possible tonight. && .LONG TERM /TUESDAY THROUGH MONDAY/... Issued at 310 PM EDT Mon Jun 29 2026 Wednesday Afternoon - Friday Night... Anomalous upper ridge persists over the region, although the center will shift slightly east to the central Appalachians. Still enough influence to keep us hot, muggy, and mostly dry. Forecast soundings for this time do show a weakened mid level cap/subsidence inversion, however without any real triggering mechanism, not sure we'll be able to tap into the strong unstable airmass characterized by 4000- 5000 J/KG of CAPE, at least not through Wednesday. There is an alternate scenario that could play out, however it is the less likely outcome at this point. See more details in the "Alternate Scenario" section below. Oppressive heat will continue to be the story through mid to late week. Temperatures are expected to reach solidly into the mid 90s along with dew points well into the 70s each day. This should continue to yield max afternoon heat indices mostly in the 100 to 110F range through at least Thursday. As we get into later Thursday and Friday, the upper ridge does center more on the mid-Atlantic with slightly less influence over our area. Chances for isolated to widely scattered diurnally driven thunderstorms will increase by this time. Forecast soundings show strong instability with little to no vertical shear, so storm modes would certainly be pulse in nature. Given slow storm movement, and potential for intense rainfall rates due to the amount instability and notably high PWATs, do think we could start running into some isolated Flash Flood concerns for areas that have already been hit hard. Something to watch in this pattern. Hopefully, given the lack of a strong trigger other than diurnal heating, coverage will be sparse in nature. We'll also have to watch for some marginally severe hail or microburst winds with the pulse storm modes. Saturday - Monday... The upper ridge steadily breaks down through the weekend with a belt of progressive zonal westerlies starting to gain influence into our region. Fine details are lower confidence, however there is a general consensus of at least a shortwave or two embedded within this flow acting as a trigger for more scattered to numerous shower and storm coverage. The best signal is for late weekend into early next week (Sunday or Monday) when a more pronounced shortwave may progress through the region, along with a surface cold front. Don't love the look of the more active pattern through the weekend followed by a frontal boundary passage given continued slow storm movement thanks to weak deep layer shear. We could end up with another weekend filled with dual threat storms capable of localized severe winds and/or localized flash flooding. The good news is that any tornado threats will not be realized in this type of environment. This is definitely more of a mid to late Summer type of setup. Another piece of good news is that this should provide some relief from the heat, however we will still likely be at or just above normal for temps ahead of this expected cool front. "Alternate Scenario" There is one scenario that we should keep in the back of our mind, and it has been shown on two consistent runs of the GFS. In this environment, we can be conducive to "chain reaction" type events where a single pulse storm can cause an eventual large complex of storms given multiple generation updrafts being triggered by the previous pulse storm collapsing. These can become quite chaotic, especially given the amount of available CAPE expected under the upper ridge. Any large complex of storms caused by this chain reaction scenario, or an upstream MCS could wreck the mid to late week temp forecast, and it has happened before. It looks looks like the earliest this could happen would be later Wednesday, however it would become increasingly possible moreso on Thursday or Friday. We'll at least have 3 solid days of oppressive heat/humidity before this occurs, so still felt the duration based Extreme Heat Warning is warranted regardless of if an MCS could bust temps late week. && .AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 130 PM EDT Mon Jun 29 2026 High pressure at the surface and aloft will control the region for this TAF cycle, and for the upcoming week. Look for Sct-Bkn cumulus clouds between 3500-4500 ft this afternoon. Light to steady SSW wind between 5 and 10 mph are expected during the afternoon, with light winds overnight. Can't rule out some patchy fog given the amount of low level moisture, however upper sky cover and some light winds keeping the low levels mixed may be just enough to mitigate the fog potential. Will leave it out for now with low confidence. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...Extreme Heat Warning until 9 PM EDT /8 PM CDT/ Thursday for KYZ023>043-045>049-053>057-061>067-070>078-081-082. IN...Extreme Heat Warning until 9 PM EDT /8 PM CDT/ Thursday for INZ076>079-083-084-089>092. && $$ SHORT TERM...BJS LONG TERM...BJS AVIATION...BJS