Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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610 FXUS63 KLSX 021759 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1259 PM CDT Tue Jul 2 2024 .KEY MESSAGES... - Several rounds of thunderstorms are expected through Thursday with a risk for severe weather and locally heavy rainfall with possible flash flooding. - The first round of strong to severe thunderstorms will be this evening over parts of central and northeast Missouri into west central Illinois. - Hot and humid weather is expected over parts of the area through Thursday. Heat index values over central and northeast Missouri will climb above 100 degrees this afternoon. && .SHORT TERM... (Through Late Wednesday Afternoon) Issued at 330 AM CDT Tue Jul 2 2024 Dry weather is expected today before a upper trough currently over the Rockies moves into the Missouri Valley by this evening. The ascent caused by trough will cause thunderstorms to develop along a front across northwest Missouri and southwest Iowa this afternoon. These storms are expected to eventually move east into the northern CWA by this evening. MLCAPES of 1000-2000+ J/kg and deep layer shear of 30-40 knots suggests that these storms should be able to continue to be severe as they move into northeast Missouri before decreasing in strength as they move east during the late evening and early overnight hours as the instability diminishes to the south and east. Available CAMS are showing the most likely mode will be linear by the time the storms move into the CWA, so damaging winds remains the primary threat along with a brief QLCS tornado. Large hail is also possible. I also expect locally heavy rainfall as PWATS will be over 2-2.5" and there will be deep warm cloud depths. Have held off on issuing a Flood Watch as CAMS are showing progressive storm motions and little potential for training at this time. The coverage of showers and thunderstorms will decrease they move to the southeast overnight as ascent from the upper trough moves off to the northeast and the instability will decrease farther to the south and east. There will be the potential for mainly scattered shower and thunderstorm development on Wednesday as the cold front/outflow boundary moves southeast through the CWA. Given the CAPE/shear parameters over southeast Missouri into southwest Illinois tomorrow afternoon, a few severe thunderstorms will be capable of producing damaging winds. Winds have shifted to the south-southeast over the area as the surface high has now moved into the northeast CONUS. Higher humidity will stream back into the western CWA with 70 dewpoints expected over central and northeast Missouri by this afternoon. With highs climbing back into the lower to middle 90s today, heat index values will be in the 100-105 degree range over central Missouri today. Highs tomorrow will be in the upper 80s to lower 90s as the front/outflow boundary moves across the area. Still with dewpoints in the lower-mid 70s, some locations over southeast Missouri will have heat index readings near 105. Britt && .LONG TERM... (Wednesday Night through Monday) Issued at 330 AM CDT Tue Jul 2 2024 The best chance for thunderstorms (70-90%) during the entire forecast period areawide will continue to be late Wednesday night into Thursday morning when there will be the another upper trough moving along the front and a 35 knot low level jet setting up strong moisture convergence over the area. Both the ECMWF and the GEFS are showing PWATS that are at the max climatology for the date pointing to the potential for locally heavy rainfall. Then there will be the potential for another round for severe weather on Thursday afternoon and evening when yet another shortwave trough will interact with a front over central and southeast Missouri. The LREF is showing MLCAPES of 2000-2500 J/kg and deep layer shear around 30-40 knots which suggests that a few severe storms will be capable of producing large hail and damaging winds. The LREF is showing that a cold front should move through the area on Thursday night which will keep high chance/likely POPs (40-60%) for showers and thunderstorms. Here again the the atmosphere will remain conducive the locally heavy rainfall until this fronts moves through the area. Then high pressure will move across Missouri and Illinois and most of the LREF members are showing the area dry Friday night through Saturday night before next trough approaches the area late in the weekend and early next week. Britt && .AVIATION... (For the 18z TAFs through 18z Wednesday Afternoon) Issued at 1245 PM CDT Tue Jul 2 2024 The primary aviation concern through Wednesday will be thunderstorms ahead of a cold front which will move through the area tomorrow morning. The ongoing convection over Iowa is expected to strengthen and become more organized this afternoon into early evening and move into northeast Missouri and west central Illinois between 02-05Z. The convection will probably be weakening as it moves into the area, but will still be capable of producing wind gusts to 40-50kts and IFR visibility in heavy downpours across northeast Missouri and west central Illinois. The storms should continue weakening, and they should largely be down to isolated/scattered showers by 12Z Wednesday across central and east central Missouri into southwest Illinois. Thunderstorms are likely to redevelop Wednesday afternoon across southeast Missouri along the cold front. Carney && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX