Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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643 FXUS63 KLSX 200906 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 406 AM CDT Fri Sep 20 2024 .KEY MESSAGES... -Scattered showers and thunderstorms (20 to 30% chance) are possible through this evening. An isolated strong to severe storm over southeast Missouri and southwest Missouri is possible this afternoon and this evening. -Several rounds of showers and thunderstorms (50-90% chance) and locally heavy rainfall are expected between Saturday and Monday night, with the best chance north I-70 between Saturday night and Monday morning. Isolated strong to possibly severe storms and locally will be possible on Sunday. -Temperatures are expected to be above normal through tomorrow, but then back to near normal starting on Monday. && .SHORT TERM... (Through Late Saturday Afternoon) Issued at 405 AM CDT Fri Sep 20 2024 The latest surface analysis is showing a front extending from central Iowa through northwest Missouri into northwest Oklahoma. Thunderstorms that had earlier developed across Iowa have shown a gradual weakening trend as they have moved southeast into less instability early this morning. I have continued with lows PoPs (20- 30%) through today as the front will continue to move east across the CWA including early this morning when convergence increases on the nose of the low level jet. Chances will continue this afternoon into this evening over southwest Illinois into southeast Missouri when MLCAPES are expected to climb into the 2000-3000 J/kg range with deep layer shear up to 30 knots. This would support one or two strong to severe storms capable of producing downburst and perhaps some large hail. There will be a better chance (40-70%) on Saturday morning when showers and thunderstorms develop along a warm front that will move through the area during the day. Both the NAM/GFS are showing a 35 knot low level jet developing over the Plains late Friday night that will bring the best chance for showers and thunderstorms into central Missouri on Saturday morning. High today will once again be around 90 degrees with 850mb temperatures around 20C and sufficient sunshine. Highs tomorrow will be mainly 80s and with the coolest reading where there be the most clouds and rain. Britt && .LONG TERM... (Saturday Night through Thursday) Issued at 405 AM CDT Fri Sep 20 2024 The unsettled weather pattern will continue into early next week as the medium range models are showing the upper ridge that has been over the central CONUS shifting to the east and the low in the Southwest lifting out and moving across the Midwest. The highest PoPS (70-90%) will be Saturday night into Sunday when a initial shortwave trough will move out across the area as cold front moves back southeast across the area. There will be a few strong to possibly severe storms given CAPE/shear parameter space and some locally heavy rainfall is also possible as PWATS will be near 2". There will also be likely PoPs (60-70%) going Sunday night into Monday night as the main upper trough and attendant cold front moves across the area. Chances for rain the rest of the week are low as the LREF is showing a large area of high pressure moving across the area with most members (<15%) not producing any precipitation after Monday night. Temperatures will fall back closer to normal behind the cold front beginning on Sunday and staying there most of next week. Britt && .AVIATION... (For the 06z TAFs through 06z Friday Night) Issued at 1045 PM CDT Thu Sep 19 2024 It is becoming more evident that any potential for showers and thunderstorms will originate out of Iowa late tonight into early Friday morning. However, how long thunderstorms survive is in question as support is limited the further southeast of ongoing development. Latest trends look as though any activity that makes it into KUIN will be delayed by an hour or two, which is reflected in this update. Guidance has continued to show a void in activity over central Missouri with the far southwest tail of the convection skimming north of KCOU, but weakening as convection moves southeast into a relatively more stable airmass. VCTS was maintained at KCOU but the window was limited to just a couple of hours. I felt comfortable enough to pull VCTS out of KJEF given the latest trends. Held onto VCTS over the metro terminals with a slight delay in arrival and also reduced the timeframe by an hour as convection looks weak and scattered through early Friday morning. The most notable chance was the addition of VCTS at metro terminals Friday afternoon/early evening. This may end up being the best chance with better instability available through peak diurnal heating. As stated in earlier forecasts, potential for direct impacts are low, but could result in a brief period of MVFR vsby. Otherwise, VFR conditions are forecast the majority of the period at all sites. Maples && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX