


Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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664 FXUS63 KLSX 230329 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1029 PM CDT Sun Jun 22 2025 .KEY MESSAGES... - The Extreme Heat Warning and Heat Advisory continue in the forecast into Tuesday evening. Dangerous heat index values in excess of 100 degrees are expected. - The weather pattern may not shift until later in the week which could extend this period of dangerous heat through Thursday or Friday. && .SHORT TERM... (Through Late Monday Afternoon) Issued at 229 PM CDT Sun Jun 22 2025 Little change in thinking from previous forecasts this afternoon. A high amplitude pattern has been established over the CONUS with a strong upper level ridge currently centered over the Ohio Valley, and a long wave trough over the Rocky Mountains. Dew point temperatures are remaining in the low 70s so far this afternoon despite soundings showing mixing up to 850mb. Heat index values reached the triple digits yesterday, and many locations are already at or above 100 degrees already today. The center of the upper high will drift a bit eastward tonight and Monday, but not far enough to make any difference in the sensible weather at the surface. A few models develop isolated convection over the eastern Ozarks during the afternoon, which would certainly affect afternoon temperatures. However, if storms develop they should be few and far between, and most locations should see heat index values between 100 and 105 again Monday afternoon. Heat headlines will therefore continue unchanged for this update. Carney && .LONG TERM... (Monday Night through Next Sunday) Issued at 229 PM CDT Sun Jun 22 2025 The pattern remains fairly stagnant at least through Wednesday with the upper ridge locked in over the southeastern quarter of the CONUS and a long wave trough over the Rockies. Temperatures/heat index values will depend largely on if/where isolated-widely scattered convection develops in the afternoon, and potentially any convective debris that wanders into the area from overnight MCS activity that would limit insolation. With that said, the NBM`s interquartile temperature range is only 2-3 degrees at most locations in the forecast area through Thursday, indicating a high degree of confidence. Parts of southeast Missouri show a 3-5 degree range, which is most likely due to afternoon convection over the eastern Ozarks in some members of the ensemble. All of the bias corrected temperature guidance is cooler than the straight deterministic guidance, which I think is dragging down the NBM mean temperatures. Therefore I`m continuing to lean on the 75th percentile for temperatures through Thursday which will keep highs in the mid to upper 90s in most locations and heat index values around the century mark. Heat headlines may need to be extended in this case, but I feel there`s enough uncertainty regarding the effects of potential afternoon convection that I`m holding off at this time. The GFS and ECMWF have consistently been showing a short wave moving from the northern Plains Thursday into the Upper Midwest and southeast Canada by Friday evening. The wave attenuates the ridge over the Mississippi Valley somewhat which could lower temperatures a few degrees for Friday through Sunday, and increase the chance for rain a bit. However, dewpoint temperatures should remain in the 70s across most of the area which will produce heat index values in the mid 90s to around 100. Carney && .AVIATION... (For the 06z TAFs through 06z Monday Night) Issued at 1028 PM CDT Sun Jun 22 2025 Mostly clear skies are expected to persist through much of the period. Clouds will slide from northwest to southeast Monday afternoon/evening from unsettled weather well to the north. Fortunately, only few mid/high clouds are forecast over metro terminals, thickening to scattered/broken sky conditions from central MO northeast through KUIN. VFR will persist through late Monday evening. 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