080 FXUS63 KLSX 292315 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 615 PM CDT Mon Jun 29 2026 .KEY MESSAGES... - An Extreme Heat Warning and Heat Advisory remain in effect through Friday for daily dangerous heat index values of 100-105 degrees. - While confidence in specifics is low, the Fourth of July weekend will be warm and muggy, with a daily threat of isolated to scattered showers and thunderstorms. && .SHORT TERM... (Through Late Tuesday Night) Issued at 230 PM CDT Mon Jun 29 2026 A highly amplified upper-level ridge can bee seen in current water vapor imagery centered over the Midwest, with an expansive surface high impacting much of the east-southeastern portion of the CONUS. Both features are keeping our skies mostly clear and south- southwesterly flow deep, leading to another hot and muggy day across the CWA. With temperatures topping out in the mid 90s this afternoon and dew points in the mid to upper 70s, heat index values will once again reach 100-105 degrees. Thanks to the ridge only amplifying and expanding further into Tuesday, the forecast will be nearly identical to today's. With these confidence high in these conditions continuing through the workweek, the current Excessive Heat Warning and Heat Advisory will remain in effect and are unchanged. Elmore && .LONG TERM... (Wednesday through Next Monday) Issued at 230 PM CDT Mon Jun 29 2026 Guidance consensus is that the upper-level ridge will dictate our local weather through the extend period, but once we reach the holiday weekend, confidence decreases in specifics. The ridge remains in place across the eastern CONUS through Thursday, with 850 mb temperatures continuing to gradually decrease. These cooler low to mid-level temperatures will increase the chance for air mass convection across the region. While Thursday's forecast is dry for much of the area, we will have to monitor a very subtle disturbance swirling beneath the center of the ridge across the Ohio Valley. If it is able to drift eastward enough, portions of southern Illinois may see greater rain chances than currently forecast. The ridge deamplifies and broadens Friday into the weekend, which will open the CWA to additional convection as well as further cool 850 mb temperatures. Run-to-run consistency and guidance spread is enough that confidence remains low on convective forcing mechanisms and the degree of any potential cooling, with the 75th percentile of ensemble guidance favoring highs in the mid 90s, with the 25th percentile around 90 degrees. If the warmer scenario comes to fruition, heat headlines would need to be continued beyond Friday for at least portions of the CWA, while the cooler scenario would lead to a break from the extreme heat for a majority of the area. While the current forecast/NBM leans more toward the warmer solution, fluctuations are expect in the coming days as guidance hones in on a common solution. Elmore && .AVIATION... (For the 00z TAFs through 00z Tuesday Evening) Issued at 611 PM CDT Mon Jun 29 2026 Dry and VFR conditions are expected through the period. South to southwesterly winds are expected to increase by 15Z on Tuesday with gusts between 20-25 knots. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Heat Advisory until 10 PM CDT Friday for Audrain MO-Boone MO- Callaway MO-Cole MO-Crawford MO-Gasconade MO-Iron MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-Marion MO-Moniteau MO- Monroe MO-Montgomery MO-Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Francois MO-Shelby MO-Washington MO. Extreme Heat Warning until 10 PM CDT Friday for Franklin MO- Jefferson MO-Saint Charles MO-Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO. IL...Heat Advisory until 10 PM CDT Friday for Adams IL-Bond IL-Brown IL-Calhoun IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL- Marion IL-Montgomery IL-Pike IL. Extreme Heat Warning until 10 PM CDT Friday for Clinton IL- Madison IL-Monroe IL-Randolph IL-Saint Clair IL-Washington IL. && $$ WFO LSX