032 FXUS63 KLSX 221112 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 612 AM CDT Sun Jun 22 2025 .KEY MESSAGES... - Confidence is increasing in heat index values around 100 degrees lasting through the end of this week. && .SHORT TERM... (Through Late Monday Afternoon) Issued at 218 AM CDT Sun Jun 22 2025 Dangerous heat continues to plague the region as an upper level ridge continues to spin over the eastern half of the CONUS. This feature and its surface reflection will remain largely in place for the next few days and will keep today's sensible weather very similar to yesterday's. Heat index values are again forecast to reach 100 areawide with the St. Louis area and southwest Illinois peaking around 105 degrees. Lows remain steady as well with widespread mid-70s forecast. A cold front is forecast to push through the northern Plains tonight and stall just north of the forecast area by Monday night. Ahead of the front, isolated showers are possible Monday afternoon. The best upper level support will be along the front to our north, so any convection will be driven by diurnal heating. Locations that see rain have the potential to temporarily cool. If it falls in the early afternoon, this may be enough to shave a degree or two off the high temperature, but it won't be enough provide relief from the heat. If it falls past mid-afternoon, afternoon highs will be established and it won't matter. Areawide broken diurnal cumulus is expected outside of the showers. This in itself will inhibit heating. On top of this, the center of the mid-level ridge slides east and 850 mb temperatures fall slightly. With these factors in mind, I inched Monday's high temperatures down by a couple of degrees. A failure point in my forecast is if deep boundary layer mixing negates the cooling factors discussed. Jaja && .LONG TERM... (Monday Night through Saturday) Issued at 218 AM CDT Sun Jun 22 2025 Tuesday will be a very similar day to Monday albeit with a slightly higher potential for showers and thunderstorms. The same forecast holds true in terms of the nature and impacts of convection, a widespread broken cumulus deck, and mixing being a factor in the forecast. I did pull Tuesday's temperatures down a degree or two as well due to the similarities. Regardless of Monday and Tuesday's highs being lowered, heat index values will still meet criteria both days so the Heat Advisory and Extreme Heat Warning have not been edited. Confidence is increasing that the mid-level ridge will stick around beyond mid-week. This is corroborated by consensus in deterministic models which depict the ridge eroding and sliding east on Thursday. This translates to greater confidence in the heat lasting longer than initially anticipated. Our current maximum heat index values on Wednesday and Thursday both have portions of the forecast area reaching 100 degrees again. If confidence in this continues to grow, parts of the Heat Advisory will need to be extended. The only mitigating factor is the potential for more convection during the mid to late week that may dampen the potential of meeting criteria. Jaja && .AVIATION... (For the 12z TAFs through 12z Monday Morning) Issued at 610 AM CDT Sun Jun 22 2025 Dry and VFR conditions will prevail through the TAF period. Some VFR diurnal cumulus is expected this afternoon. Otherwise, winds will pick up from the south again today and will become gusty in portions of central and northeast Missouri as well as west-central Illinois. Cumulus and winds will diminish after sunset. Jaja && .CLIMATE... Issued at 1225 PM CDT Thu Jun 19 2025 Record maximum temperatures at St. Louis, MO (STL), Columbia, MO (COU), and Quincy, IL (UIN) along with the year of the record: | 6/22 | 6/23 | 6/24 | 6/25 ------------------------------------------------------- STL | 102 (1930) | 101 (1930) | 102 (1988) | 103 (2024) | | | | COU | 100 (1988) | 100 (1988) | 103 (1988) | 102 (1988) | | | | UIN | 100 (1930) | 100 (1934) | 99 (1988) | 102 (1931) Record high minimum temperatures at St. Louis, MO (STL), Columbia, MO (COU), and Quincy, IL (UIN) along with the year of the record: | 6/22 | 6/23 | 6/24 | 6/25 ------------------------------------------------------ STL | 80 (2016) | 80 (2010) | 80 (1914) | 82 (1988) | | | | COU | 77 (1944) | 76 (2010) | 77 (1937) | 77 (1988) | | | | UIN | 78 (1944) | 80 (1944) | 79 (1931) | 80 (1937) && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Heat Advisory until 9 PM CDT Tuesday for Audrain MO-Boone MO- Callaway MO-Cole MO-Crawford MO-Franklin 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-Sainte Genevieve MO-Shelby MO-Warren MO-Washington MO. Extreme Heat Warning until 9 PM CDT Tuesday for Jefferson MO- Saint Charles MO-Saint Louis City MO-Saint Louis MO. IL...Heat Advisory until 9 PM CDT Tuesday for Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Macoupin IL- Marion IL-Montgomery IL-Pike IL-Randolph IL-Washington IL. Extreme Heat Warning until 9 PM CDT Tuesday for Jersey IL- Madison IL-Monroe IL-Saint Clair IL. && $$ WFO LSX