


Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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272 FXUS63 KLSX 110004 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 704 PM CDT Thu Jul 10 2025 .KEY MESSAGES... - Multiple rounds of showers and thunderstorms are expected late Friday through the weekend. A few severe thunderstorms are possible Friday evening cross northeastern MO and west- central IL along with locally heavy rainfall and isolated flash flooding. - Hot and humid conditions are forecast on Friday with peak heat index values reaching the upper 90s to near 105 F, highest in the St. Louis metro. Temperatures will cool through the weekend. && .SHORT TERM... (Through Late Friday Night) Issued at 233 PM CDT Thu Jul 10 2025 An upper-level trough will continue passing through the Midwest this afternoon and evening. However, with large-scale ascent passing mainly north of the CWA, weak capping inversions, and a lack of low- level convergence, only a stray shower/thunderstorm or two is expected at most across northeastern MO/west-central IL this evening. A shortwave ridge with rising mid-level heights will be unfavorable for any showers and thunderstorms overnight/Friday morning across IA into northern IL from advancing south/southeastward into the CWA. Therefore, predominantly dry conditions are expected through midday Friday. Weak low-level southerly flow/WAA will lead to slightly warmer high temperatures on Friday in the low to mid-90s F. With increasing moisture and dewpoints in the 70s F with some upper 60s F during peak afternoon heating/BL mixing, peak heat index values in the upper 90s to near 105 F are forecast, highest in the St. Louis metro. Around 20 percent of HREF membership has isolated showers and thunderstorms developing during the afternoon across the Ozarks and southwestern IL with a signal for weak surface convergence (possibly topographically enhanced) and convective temperatures to be reached. A weak microburst with gusty winds cannot be ruled out, but warm mid- level temperatures/weak lapse rates and weak deep-layer wind shear may limit updraft strength. Instead, the main focus of showers and thunderstorms will be across southern IA and northern MO during the afternoon and evening as a shortwave trough overspreads a cold front and other remnant outflow boundaries. It is uncertain how quickly these showers and thunderstorms will advance south/southeastward into northeastern MO and west-central IL with CAMs indicating an arrival as early as 4 pm and late as 8 pm, depending on how quickly cold pool development can occur. Deep-layer wind shear of 20 to 25 kt and MLCAPE of 2000 to 3000 J/kg will favor mainly multicell thunderstorms or an MCS with damaging winds and marginally severe hail. With deep warm cloud depths, PW approaching 2", and the potential for cell training and backbuilding into a 35 kt-southwesterly LLJ there is also a threat of locally heavy rainfall and isolated flash flooding. All of these threats are highest across northeastern MO and west-central IL with showers and thunderstorms expected to gradually weaken with time and southward extent Friday night as they become increasingly outflow dominant. Pfahler && .LONG TERM... (Saturday through Next Thursday) Issued at 233 PM CDT Thu Jul 10 2025 On Saturday, the cold front will reach the CWA before it slows and possibly wavers across the region over the weekend. There should be an overall southeastward progression of the front with time, but this progression is uncertain due to the impact of multiple passing mid-level shortwave troughs/MCVs within a variable period of southwesterly flow and associated showers and thunderstorms. Therefore, ensemble membership has a broad-brushed area of 50 to 70 percent probabilities of measurable rainfall that encompass most of the CWA on Saturday and then shift to southeastern MO and southwestern IL on Sunday. With the slow front, slow or training cell motions, and PW straddling 2", the threat of locally heavy rainfall will exist but whether or not flash flooding occurs will hinge on mesoscale details that are still uncertain. With weak deep- layer wind shear, confidence is low in any organized severe thunderstorms over the weekend. With a gradual passage of the front over the weekend and increasing clouds and precipitation, a cooling trend will take place over the weekend with near/slightly below average high temperatures in the 80s F nearly CWA-wide by Sunday. A broad upper-level ridge will briefly dominate the Mid-Mississippi River Valley Monday into Tuesday, allowing the aforementioned front to eventually lift back northward along with the most favorable corridor of showers and thunderstorms. However, there are little signs of any appreciable large-scale forcing with mainly scattered diurnal showers and thunderstorms expected. Global model guidance thereafter is in general agreement in another relatively active/wet period during the middle of next week with upper-level quasi-zonal to southwesterly flow and multiple passing shortwave troughs/perturbations. The NBM high temperature distribution is also reasonably clustered (3 to 5 F IQR) on a warming trend to near or slightly above average through the first half of the week along with another increase in moisture/dewpoints. Pfahler && .AVIATION... (For the 00z TAFs through 00z Friday Evening) Issued at 701 PM CDT Thu Jul 10 2025 VFR conditions are expected throughout the 00Z TAF period. Overnight, there remains a low chance of a few showers primarily at UIN, but the probability of impacts to the terminal remains too low for inclusion in the TAF. By tomorrow afternoon, more VFR level cumulus is likely to develop, and a few stray showers or weak thunderstorms may develop primarily to the north and south of local terminals. However, there is another low chance (10-20%) chance for showers to develop locally as well, again too unlikely for TAF inclusion. Best chances for showers and thunderstorms exist just after the end of the cycle, and will likely be included a the end of the 06Z TAF. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX