704 FXUS63 KLSX 160322 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1022 PM CDT Wed May 15 2024 .KEY MESSAGES... - Unsettled weather returns to the region late tonight through Friday. Isolated strong to severe thunderstorms are possible Thursday afternoon and evening. - Portions of southeast Missouri and southwest Illinois could see locally heavy rainfall that could produce minor flooding on Friday. - Warmer weather returns to the region late in the weekend and through next week. Temperatures will be around 10 degrees above normal by Monday and Tuesday. && .SHORT TERM... (Through Late Thursday Night) Issued at 237 PM CDT Wed May 15 2024 A weak surface ridge will continue to slide off to the southeast tonight as the next system over the Northern/Central Plains moves into western MO by 06z Thursday. A warm front will develop along the MO/AR border this evening and lift northward as an upper level shortwave associated with the system lifts northeastward out of the Southern Plains. Still some uncertainty on the exact location of the warm front through the period and where the main axis of showers and storms will develop. The latest deterministic model runs range from across northern MO (NAM) to across southern MO (GFS), while the majority of the HREF ensembles have the main axis along and south of I-70 tonight through Thursday. So kept the highest POPs along and south of I-70. Since the activity will take awhile to reach the region, still have high confidence that it will be weakening as it moves into the area due to weakening instability and veering low level jet. There is still some uncertainty on how much the atmosphere will recover by Thursday afternoon due to the morning rain and cloud cover. However, as a remnant MCV, associated with the morning activity, slides along the MO/AR border Thursday afternoon combined with MU CAPEs between 1000-2000 J/kg and 0 to 6km bulk shear of 30 to 40 kts, could see isolated severe storms develop over southeast Missouri and southwest Illinois, as well as a small portion of east-central Missouri. The main threats will be damaging winds and large hail between 2 pm and 8 pm Thursday. The activity will taper off by late evening Thursday with the boundary stalling out along the MO/AR border. This boundary will be the focus for additional activity developing after 06z Friday as the main shortwave/trough over the TX panhandle slowly slides east northeast towards the region. Byrd && .LONG TERM... (Friday through Next Wednesday) Issued at 237 PM CDT Wed May 15 2024 The shortwave with associated surface low will continue to slide east northeast on Friday towards the forecast area. With the surface boundary lingering across southern Missouri, the combination of a southerly low level jet (25 to 35 kts), PWATS in excess of 1.5 inches and deep layer ascent at the left exit region of the upper jet will generate widespread showers and storms. Thus portions of southeast Missouri and southwest Illinois could see locally heavy rainfall that could produce minor flooding on Friday. The latest ensembles as well as deterministic models still have differences in timing, strength and location of the system as moves through the region this weekend. For now still expect low chances (20-40%) of showers and a few storms Friday night through Saturday, especially across portions of east-central/southeast Missouri and southwest/south-central Illinois. Otherwise, a majority of the region will be dry this weekend. Beyond the weekend, warmer weather is expected with above normal temperatures by Monday and Tuesday. Otherwise, there is the potential for another active period as multiple shortwaves move across the region. Byrd && .AVIATION... (For the 06z TAFs through 06z Thursday Night) Issued at 1010 PM CDT Wed May 15 2024 Primary concern throughout the 06Z TAF period will be the potential for scattered thunderstorms at various times, along with lowering ceilings. A few weak showers and thunderstorms have already developed in the vicinity of COU/JEF as of 03Z, and this initial activity may periodically impact these areas over the next several hours and into the beginning of the TAF period. More widespread showers and a few thunderstorms are expected to move into this area near daybreak and spread east, likely impacting all terminals to varying degrees. This round is also likely to drop ceilings to MVFR levels at times, potentially visibilities as well. A lull in shower activity is likely after this initial round by mid afternoon. However, redeveloping thunderstorms will be possible in the late afternoon and evening. Most of this activity is likely to remain south of local terminals, but additional showers and storms will be possible at all terminals. St. Louis area terminals would be most likely to observe the strongest of these storms, and this will all likely be followed by additional showers and thunderstorms by early Friday morning. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX