Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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985 FXUS63 KLSX 142006 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 306 PM CDT Tue May 14 2024 .KEY MESSAGES... - Showers and isolated thunderstorms will diminish this evening and exit to the east overnight. Isolated instances of heavy rain are possible through this evening. - Active weather will return late Wednesday night and continue through at least Friday with periods of showers and thunderstorms impacting parts of the area, including the potential for strong storms Thursday afternoon and evening. - Above normal temperatures return next weekend and continue into early next week. && .SHORT TERM... (Through Late Wednesday Night) Issued at 225 PM CDT Tue May 14 2024 The slow-moving upper low was located over central MO at mid- afternoon. More continuous/banded showers and scattered thunderstorms were located in advance of the low stretching from far southeast MO through southwest and west-central IL, while further west more diurnally driven scattered showers and isolated storms were rotating cyclonically about the mid-upper circulation feeding off SBCAPE of 1000-1500+ J/KG. The aforementioned band will continue to shift slowly east through the remainder of the afternoon bringing some locally heavy downpours and pockets of heavy rain, owing to more persistence and a very moist air mass/higher rain rates. The trend heading through the early-mid evening should be a decrease in coverage of showers/thunderstorms as the diurnally driven instability wanes and the upper low moves to the east-southeast. All of the precipitation should exit the area overnight as the upper low moves into the Ohio Valley. Stratus is expected to hang tough across the area overnight and any breaks could result in locally areas of fog. All-in-all, a lot of cloudiness is expected to persist on Wednesday. The stratus will diminish as clouds become more cumuliform heading into the afternoon, with below normal temps. The active weather regime will then resume late Wednesday night. A broader trof will move into the upper MS Valley with a well- defined vort max tracking into the area overnight. This disturbance along with a returning warm front and increasing southwesterly LLJ should support showers and thunderstorms moving into at least central and portions of eastern MO between 06-12Z Thursday. The activity could be weakening convection originating from the central Plains and/or additional elevated development. Glass && .LONG TERM... (Thursday through Next Tuesday) Issued at 225 PM CDT Tue May 14 2024 The expectation is showers and thunderstorms will be ongoing at daybreak Thursday, probably west of the MS River, supported by the aforementioned mid-level disturbance and LLJ. This activity will likely move east across the CWA through the morning with potential for additional development trailing in its wake. Later on Thursday afternoon and night, the presence of a lingering east-west boundary across the southern part of MO and southern IL is likely to be the catalyst for additional rounds of showers and storms with MLCAPE forecast from 1500-2500 J/KG. Sufficient deep layer shear on the order of 30 kts should be present to support potential for organized storms, including a few strong-severe storms. The forecast for Friday into early Saturday is a bit more muddled. There are differences in the upper level trof structure/position and timing with a trof translating eastward from the southwest U.S. across the Plains which adds uncertainty to the forecast. Most of the guidance shows only nebulous forcing Friday and a lack of a surface boundary but plentiful instability, at least supporting a threat of showers and thunderstorms. I suspect that this trof will have passed to the east by early Saturday and the majority of the weekend will be dry with a warming trend. Differences in details of the large scale regime persist into early next week. There is good agreement the flow aloft will become more southwesterly with potential short waves tracking within it bringing more thunderstorms chances, but uncertainty is high in the timing and details. Temperatures should return to above normal this coming weekend and continue through early next week. Glass && .AVIATION... (For the 18z TAFs through 18z Wednesday Afternoon) Issued at 1250 PM CDT Tue May 14 2024 The main band of showers and thunderstorms was located between KSUS and KCPS and will continue to rotate east-northeast through the afternoon. As a result, KCPS will see the greatest impacts from reduce visibility and thunder through around 19z. Otherwise predominately MVFR flight conditions will continue through the afternoon with showers periodically impacting the terminals and resulting in brief visibility reductions. The showers should begin to pull east of all the terminals this evening, with flight conditions lowering to IFR during the late evening and overnight due to low stratus. Ceilings should slowly slowly improve mid- late morning with VFR becoming prevalent by afternoon. Glass && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX