FXUS63 KLSX 161121 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 621 AM CDT Thu Apr 16 2026 .KEY MESSAGES... - There is a chance for showers and thunderstorms this afternoon and early evening, mainly along and south of I-44 across the Eastern Ozarks. - Thunderstorms are expected to move into northeast and central Missouri late Friday afternoon or early evening and continue through the area Friday night. Some of the storms could be severe Friday afternoon and evening. && .SHORT TERM... (Through Late Tonight) Issued at 405 AM CDT Thu Apr 16 2026 The cold front which triggered last night's storms is washing out over Missouri and west central Illinois, and is now difficult to discern in surface observations. Low level southerly flow will be reestablished across the area today ahead of the tail end of the mid- upper level trough which was pushing the front southeast. The trough is attenuating quickly, and 500mb heights are forecast to either be steady or even rise slightly just ahead of it. However, most short-range guidance is showing low level moisture convergence on the southerly flow, and they produce a few hundredths of an inch of QPF. Several CAMs (including the latest HRRR) pop up scattered convection over the eastern Ozarks during the afternoon as well. GFS and RAP show a solid 1500-2500 J/Kg SBCAPE south of I-70 in Missouri into far southeast Illinois, along with 30-40kts of 0-6km shear. Forecast soundings look nearly uncapped with perhaps just the slightest amount of CINH. However, the only obvious trigger for afternoon thunderstorms is the aforementioned weak low level moisture convergence, which may not be enough to force convective initiation. With all that in mind, I do think 30-40 PoPs are warranted across the eastern Ozarks this afternoon into early evening, and I would not be surprised if a few severe thunderstorm warnings were issued. The mid-upper level trough will be moving east of the area and short wave ridging will build across the Mid- Mississippi Valley this evening, so any storms that do develop during the afternoon should either move out of our forecast area or dissipate between 00-03Z this evening. Remaining cloud cover left over from overnight convection should clear the Mississippi River by 15-16Z and then be out of south central Illinois by 17- 18Z. Lack of a decent FROPA, persistent southerly flow, and strong April sunshine after clouds clear this morning should push temperatures back into the low to mid 80s today, and light southerly flow tonight will promote mild lows in the low to mid 60s in most locations. Carney && .LONG TERM... (Friday through Wednesday) Issued at 405 AM CDT Thu Apr 16 2026 Attention turns to severe weather potential Friday. A strong mid- upper level trough will move across the Plains into the Midwest Friday into Saturday. A strong cold front will develop over the eastern Plains Friday morning and move into northwest Missouri by mid-late Friday afternoon. Mid levels will cool ahead of the front as the trough moves east which will steepen lapse rates and increase instability. GFS and RAP show 3500+ J/Kg CAPE ahead of the front in northwest Missouri with deep layer shear increasing to 50kts. Convection is expected to be triggered by the front as it moves southeast during the afternoon. Supercells should be the predominant convective mode in this environment, at least initially. However, shear vectors are nearly parallel to the low level boundary which should promote upscale growth into a QLCS with LEWPs and bowing segments as it moves into northeast and central Missouri. Damaging winds will be the primary threat as the line moves into our area, and strong 0-1km shear will also produce a tornado threat. Large hail will also be a threat early on, particularly where supercells may be embedded in the line, but the hail threat should diminish as the line continues east into east central Missouri and southwest Illinois. I am still uncertain as to how far east the severe threat extends. GFS and RAP show instability falling quickly after sunset ahead of the line across eastern Missouri into southwest Illinois. CAMs also indicate the line will weaken quickly during the evening. The 4km NAM looks like the most dramatic example of this weakening as the line falls apart between 03-04Z before it reaches east central Missouri. The HRRR also weakens the line, although it's after 04Z after the line has moved nearly all the way through the CWFA. This variability does not instill a great deal of confidence in the eastward extent of the severe threat. However the solutions which hang onto evening instability and the favorable 0-1km kinematics continue to warrant the severe messaging. Briefly, beyond Friday night... Cooler and quieter weather settles into the Mid-Mississippi Valley Saturday behind the front. Cool high pressure spends the weekend moving from the Great Plains into the Lower Mississippi Valley. Seasonably cool temperatures in the 60s are expected Saturday and Sunday with lows Sunday morning dropping into the mid 30s to around 40. Low level flow returns turns back to the south early next week which will push temperatures back into the 70s to near 80. Carney && .AVIATION... (For the 12z TAFs through 12z Friday Morning) Issued at 620 AM CDT Thu Apr 16 2026 Light SSW winds are expected today under a mostly clear, VFR sky. There is a low potential for renewed thunderstorm development over southern MO and IL, but this is unlikely to occur far enough north to affect any TAF location. Kimble && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX