543 FXUS63 KLSX 300503 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1203 AM CDT Tue Apr 30 2019 .UPDATE... Issued at 938 PM CDT Mon Apr 29 2019 Thin band of showers and isolated thunderstorms is currently slowly moving northward across the central part of the CWA. This is occurring in a thin band of low level moisture convergence north of surface front which currently stretches across far southern Missouri and Illinois. This low level forcing will shift northward and increase overnight in response to increasing low level jet. This will cause an increase in showers and thunderstorms across central and northeast Missouri as well as west central Illinois which is already reflected well in going forecast. Flash flood watch starting over the northern third of the CWA still looks good as 00Z upper air analysis showed strong moisture transport into the area with KSGF PWATs around 1.5". Any thunderstorms over the northern part of the CWA overnight will have the potential for training. Britt && .SHORT TERM... (Through Late Tuesday Night) Issued at 409 PM CDT Mon Apr 29 2019 A cold front stretching from near Springfield Missouri northeast along the I-44 corridor and into south central Illinois near Effingham Illinois will continue to drift south for a few more hours this evening before moving back to the north up to near the Missouri/Iowa border by Tuesday afternoon. The northward movement is due in part to a 25-30kt low level jet tonight which will be blowing perpendicular to the baroclinic zone at 850 mb. All models are printing out QPF over a good portion of the area tonight to a greater or lesser extent due to the moisture convergence along the baroclinic zone. The NAM is particularly bullish late tonight strong moisture convergence across northeast Missouri into west central Illinois. Since some of those same areas received in excess of 1 inch (2+ in a few spots according to radar estimates) have issued a flash flood watch for those areas beginning at 06Z tonight. Attention turns to Tuesday and the severe weather threat as well as additional flooding. A shortwave aloft will be moving off the Rockies forcing cyclogenesis over the central Plains. The negatively tilted wave will move quickly to the northeast into the Missouri and Upper Mississippi Valley on Tuesday night. This will push the surface low northeast from northern Texas to southeast Iowa by 12Z Wednesday morning. 2200+ CAPE in the warm sector ahead of the low level cyclone in eastern Kansas and Missouri combined with 35-50kts of 0-6km shear will be more than enough to support severe thunderstorms on Tuesday afternoon and the CAMs are advertising a QLCS organizing in eastern Kansas or western Missouri and racing east during the late afternoon and evening. The latest HRRR looks especially strong with a prominent bow echo moving through central Missouri around 00Z. The exact timing and strength of the convection is of course difficult to determine and will depend greatly on how unstable the atmosphere can get at peak heating Tuesday afternoon. While a bow echo moving through central Missouri is certainly not good news, the silver lining may be that there will be less rain than expected earlier in northeast Missouri and west central Illinois on Tuesday night. However...it looks like the outflow boundary from the QLCS may slow and take on an east-west orientation across southern Missouri including our eastern Ozark counties. Since the shortwave which is kicking this system off is lifting out rather than digging, the 850mb front is not expected to move south with the convection. Therefore, warm and moist advection will continue across the outflow boundary Tuesday night. The GFS and especially the NAM produce very strong moisture convergence across the Ozarks and the NAM prints out areas of 2 inch or greater QPF. While this may be too high, it's not out of the realm of possibles considering precipitable water values in excess of 1.5 inches and warm cloud depths in excess of 10,000 feet. Given the potential for flash flooding not only overnight across the eastern Ozarks but also with heavy rain and lingering stratiform precip behind the QLCS, have expanded the flash flood watch further south to encompass all Missouri counties and parts of southwest Illinois as well beginning Tuesday afternoon. Both segments of the flash flood watch continue through Wednesday morning and the southern segment which includes central and eastern Missouri and parts of southwest Illinois continues until 12Z Thursday. Carney .LONG TERM... (Wednesday through Next Monday) Issued at 409 PM CDT Mon Apr 29 2019 An unsettled period will persist Wednesday into Thursday with potential for several rounds of showers and storms and heavy rain. A broad longwave trof will remain centered over the western U.S. during this time frame resulting in active southwest flow aloft with multiple disturbances in the flow aloft traversing the area and contributing to the development of convective storms. That said, while the broad scale pattern will largely be favorable for showers and storms, the convective scale and mesoscale details will ultimately impact the severe weather threat and most favorable location for heavy rain. A decaying/weakening MCS from Tuesday night should have passed through the area by daybreak Wednesday with a position expected from far southern IL/southeast MO extending southwestward into northern AR and eastern OK. There will also likely be a remnant large scale outflow boundary in this same area. It would seem only scattered showers will be impacting the immediate region during the first part of the morning, namely in the eastern CWA. So the big question will be the recovery potential for the remainder of the day on Wednesday and into the afternoon as the synoptic scale cold front begins to enter the northwest CWA. Both the GFS and NAM show relatively undiluted steep mid level lapse rates and with diurnal heating the air mass becomes quite unstable by afternoon, whereas the ECMWF is not quite as aggressive with instability. These model differences persist from Wednesday afternoon into Wednesday night. The GFS and NAM suggest a new round of convection developing late Wednesday afternoon/evening in central MO in association with a moderately strong and veering southwesterly LLJ, the aforementioned unstable air mass, and potentially in the region of the old retreating outflow and ahead of the slow eastward moving cold front. The mesoscale pattern and model QPF distribution would suggest upscale growth and the potential for either an elongated MCS or series of MCSs evolving along or south of I-70 on Wednesday night. Training potential and high moisture content would support a heavy rain threat within this region should the scenario evolve as envisioned. The instability and sufficiently strong deep layer shear would also support the potential for organized multicell storms from late afternoon into the evening. The caveat to all of the above heavy rain threat is the ECMWF generally has this scenario but focused much further south and removed from the CWA. Nonetheless we have the flash flood watch covering this time frame and location given the heavy rain and flood potential. The flow aloft will veer a bit more westerly on Thursday with the passage of the initial disturbance, allowing the cold front to finally move east and through the CWA by early Thursday evening. Depending on how the whole Wednesday night scenario evolves, showers and thunderstorms should be ongoing across eastern MO and western IL during the morning, shifting east and southeast with time as the cold front advances. I think the heaviest rain will have ended by this time frame. The flow aloft will be in transition Friday through the weekend into early next week with the eventual evolution to a split flow regime. The GFS and ECWMF do suggest that Friday/Friday night may not be dry as previously expected with both showing a low amplitude trof traversing the area and low level lift along and north of the boundary draped southern MO and southern IL. The GFS and ECWMF then diverge heading into the weekend and early next week with the large scale pattern and westerly or southwest flow aloft vs. northwest flow aloft. There does appear at this time to be another cold front passage centered sometime around Sunday, however uncertainty with accompanying precipitation with this front and into Monday is high and confidence low. Lastly...Present indications and RFC forecasts suggest a number of river forecast points on the Mississippi River above Alton will return to moderate and major flooding resulting from observed rainfall over the last 24 hours and additional rainfall forecast for the next 24 hours. All people with interests should closely monitor the forecasts and updates in the coming days due to the impacts from prolonged rainfall potential into the end of the week. Glass && .AVIATION... (For the 06z TAFs through 06z Tuesday Night) Issued at 1157 PM CDT Mon Apr 29 2019 Showers and thunderstorms are expected to continue to develop through the night and affect primarily KCOU and KUIN. This trend will continue into Tuesday with lesser chances at the St. Louis area terminals. A complex of thunderstorms will move through the area late in the afternoon into the evening bringing the chance for hail and and gusty winds in excess of 35kts. MVFR ceilings are starting initially at KUIN and KCOU, but are expected to spread during the night at all of the terminals, with some IFR ceilings. SPECIFICS FOR KSTL: Low chances for showers and thunderstorms will continue through the rest of the night into Tuesday, though best chance will remain north of the terminal. Better chance will come late tomorrow afternoon into tomorrow evening when a line of thunderstorms is expected to move into the area from the west. This line will have the potential to bring hail and gusty winds in excess of 35kts. VFR ceilings are starting out at the terminal, but MVFR and IFR ceilings are expected at times throughout the rest of the period starting at 04Z. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Flash Flood Watch from Tuesday afternoon through Thursday morning for Audrain MO-Boone MO-Callaway MO-Cole MO- Crawford MO-Franklin MO-Gasconade MO-Iron MO-Jefferson MO- Lincoln MO-Madison MO-Moniteau MO-Montgomery MO-Osage MO- Reynolds MO-Saint Charles MO-Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO- Washington MO. Flash Flood Watch through Wednesday afternoon for Knox MO-Lewis MO-Marion MO-Monroe MO-Pike MO-Ralls MO-Shelby MO. IL...Flash Flood Watch from Tuesday afternoon through Thursday morning for Calhoun IL-Jersey IL-Madison IL-Monroe IL- Randolph IL-Saint Clair IL. Flash Flood Watch through Wednesday afternoon for Adams IL-Brown IL-Greene IL-Pike IL. && $$ WFO LSX