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Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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009 FXUS63 KLSX 011727 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1227 PM CDT Mon Jul 1 2024 .KEY MESSAGES... - Another dry day is expected today with high temperatures that are 5 to 10 degrees below normal. - Hot and humid conditions will return to the area on Tuesday and Wednesday with highs ranging from the upper 80s to the middle 90s and heat index values over 100 degrees over parts of the area. - The pattern will become active with several rounds of showers and thunderstorms from Tuesday night through the end of the week. There is the risk for a few severe thunderstorms over northeast Missouri into west central Illinois on Tuesday night and across mainly southwest Illinois on Wednesday afternoon. && .SHORT TERM... (Through Late Tuesday Afternoon) Issued at 337 AM CDT Mon Jul 1 2024 Dry weather is expected to continue through at least late tomorrow afternoon. The regional radar mosaic is showing that showers and a few thunderstorms have developed over eastern Kansas in an area of low level moisture convergence. This complex will continue to move east into western Missouri before diminishing as the low level jet veers and it moves into more stable and dry air. The next chance for rain will be late tomorrow afternoon over northeast Missouri where the GFS/NAM are showing MLCAPES increasing 1500+ J/kg ahead of a cold front entering northwest Missouri. The majority of the CAMS are showing convection moving into the CWA after 00Z, so will keep just a 20-30% chance for showers and thunderstorms during the afternoon. The latest surface analysis is showing high pressure centered over the western Great Lakes with a ridge extending southward into central Missouri. This was keeping winds out of the north to northeast early this morning which was keeping a steady stream of drier and cooler air moving into the area. The latest run of the HREF is showing the high moving into the northeast CONUS by Tuesday which will cause winds to turn out of the east today and out of the south on Tuesday. Highs today will be in the mid 70s to the lower 80s given the cool start and cold/neutral advection. Temperatures tonight into Tuesday will warm up with winds turning out of the south and 850mb temperatures climbing to around 20C. Lows tonight will be in the low to mid 60s while highs tomorrow will be in the low to mid 90s. Dewpoints over central and northeast Missouri will climb into the lower to middle 70s by tomorrow afternoon pushing heat index values into the 100-105 range. Britt && .LONG TERM... (Tuesday Night through Sunday) Issued at 337 AM CDT Mon Jul 1 2024 The chance (50-80%) for showers and thunderstorms will increase over northeast Missouri and west central Illinois by Tuesday evening. Thunderstorms including supercells are expected to develop over western Missouri/southwest Iowa in advance of an upper trough/attendant cold front that will eventually congeal and move east into the northern CWA. The NAM/GFS is showing sufficient CAPE/ shear values for the storms to remain severe with the CAMS showing a QLCS the most likely storm mode. Damaging winds will be the primary threat given the CAPE/shear distribution, with a brief tornado and large hail also possible. The front will move south and stall over the CWA near I-70 under quasi-zonal flow aloft. Coverage of showers and thunderstorms will generally be scattered with the weak upper trough and attendant low moving across the area during the day. This weak lift paired with MLCAPES increasing into 2500-3000 J/kg range under 30-40 knots of deep layer shear will be enough that a few of the storms could be strong to severe, capable of producing large hail and damaging winds during the afternoon most likely over southwest Illinois. There is good agreement between the GFS/ECMWF/NAM that another shortwave trough will move across Missouri and Illinois late Wednesday night into early Thursday. This will increase rain chances into the 70-80% range with the potential for locally heavy rainfall given that PWATS will be 2+" which is in the upper 99th percentile for this date. The front will then move back as warm front during the day before another trough and attendant cold front moves across the area on Thursday night. At this point the LREF is keeping an upper trough to our north this weekend, but there is varying solutions in ensembles of additional weak troughs that will move across the Midwest that keeps 20-30% chances for showers and thunderstorms. Britt && .AVIATION... (For the 18z TAFs through 18z Tuesday Afternoon) Issued at 1227 PM CDT Mon Jul 1 2024 Predominantly dry and VFR flight conditions will prevail through the TAF period at all terminals, aside from a few sprinkles around KCOU and KJEF this afternoon. Winds are anticipated to remain light and gradually veer from easterly to southerly between this afternoon and Tuesday morning before strengthening and gusting to 18 to 25 kt by midday. Pfahler && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX