899 FXUS63 KJKL 292012 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 412 PM EDT Mon Jun 29 2026 .KEY MESSAGES... - Just a small chance for a stray shower or thunderstorm each day for most of the week. - Heat and humidity build today - likely becoming quite oppressive by mid-week. && .SHORT TERM...(This evening through Tuesday night) Issued at 412 PM EDT MON JUN 29 2026 Substantial ridging will be in place throughout the short term period of the forecast and into the extended period as well. While usually "Big Bubble" means "no trouble" in reference to the upper level ridge, that might not be the case in this instance. As the high builds in from our SE, flow will continue to be SWrly (albeit light) across eastern KY, continuing to advect in warm/moist air and also sinking it at the same time thanks to the strong subsidence. So maybe Big Bubble is changing places with it's evil twin the Heat Dome. Temperatures are forecast to rise into the mid 90s for most locations across eastern KY by Tuesday afternoon (several degrees warmer than today). The additional humidity will make it feel even warmer, with apparent temperatures (heat index) pushing the low 100s. Many places will reach heat advisory criteria again at 105 degrees. Overnight tonight and again Tuesday night will be calm, with the increasing subsidence in place. However, calm doesn't necessarily mean cool. Overnight lows will be mild at best, in the low to mid 70s. Coolest temperatures will likely occur in the deepest valleys, where enough moisture from the streams/rivers may contribute to some valley fog again overnight. Went ahead and issued an Excessive Heat Warning for the western tier or two of counties, where heat indices will be between 100 and 105 degrees across large parts of the county for 4 consecutive days (through at least Thursday). This also lines up with the Louisville office as well. The remaining CWA was placed into a Heat Advisory through the same time frame, matching our other neighboring offices. That being said, there is not a sharp cut off or lowering of temperatures from the warning to the advisory. While some counties will be a few degrees cooler, Pike County, for instance, currently has temperature forecast to get just as high as locations in the Excessive Heat Warning. But it's a starting point, at which we can then upgrade as we move into the following days, or leave as an advisory if things start to trend a few degrees lower. Either way, the messaging here is that there is going to be excessive heat, and going into a large holiday where more people will be spending time outside will make things more dangerous. .LONG TERM...(Tuesday night through Sunday) Issued at 300 AM EDT MON JUN 29 2026 The long-term period opens Tuesday evening with an ~597 dam high situated directly over the Commonwealth. At the surface, corresponding high pressure centered off the Delmarva Peninsula will exert its influence across the Southeastern US. A very hot air mass will be found under the upper-level high with 850 hPa temperatures over the eastern Kentucky Coalfields around 22C. Upstream, a 500 hPa trough will be stationed over the Western CONUS. The upper-level high will very slowly drift eastward through midweek to a position over Virginia by Thursday evening, at which point, 850 hPa temperatures over the JKL CWA will reach the zenith of the forecast period at 23 to 24C. Dew points will also be in the 70s on both days, allowing for moderate to strong destabilization on both Wednesday and Thursday, but a mid-level cap should keep a lid on most deep convection. Only isolated PoPs are found across portions of the area through Thursday. Heat indices will continue to climb each afternoon, with the hottest readings on Thursday afternoon in the 100 to 110 degree range for most areas. Relief at night will be limited, with low temperatures generally ranging in the 70s. Heading into Friday and the Independence Day weekend, the upper- level ridging will gradually break down as troughing ejects eastward. As this occurs, difficult-to-time perturbations will lead to renewed threats for more widespread, diurnally modulated convection amidst weaker capping. Model soundings suggest that continued weak shear combined with high PWATs could lead to a threat of downburst winds from stronger pulse storms. The heat will also gradually subside. While heat indices could still rise to near or above 100F through Sunday, there will have been an overall slow cooling trend as the ridge dissipates. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) ISSUED AT 212 PM EDT MON JUN 29 2026 As high pressure continues to set up across the region, subsidence is increasing. That being said, there is still enough lingering moisture and mixing this afternoon to spawn some fair-weather CU across much of eastern KY. A few small showers are also possible near the KSJS TAF in far eastern KY, but should not cause any issues other than a temporary visibility reduction. All CU and any lingering shower chances should dissipate heading into the evening hours with the loss of mixing. This will give way to mostly clear skies overnight, and the potential for some valley fog development. Did not include any fog impacts at the TAF sites at this time. Winds are also light at the TAF issuance, and should remain light through the remainder of the TAF period as well, less than 5 kts. && .JKL WATCHES/WARNINGS/ADVISORIES... Extreme Heat Warning until 8 PM EDT Thursday for KYZ044-050>052- 058>060-068-069-079-080-083>086. Heat Advisory until 8 PM EDT Thursday for KYZ087-088-104-106>120. && $$ SHORT TERM...JMW LONG TERM...GEERTSON AVIATION...JMW