134 FXUS63 KLSX 260817 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 317 AM CDT Sat Oct 26 2019 .SHORT TERM... (Through Late Sunday Afternoon) Issued at 313 AM CDT Sat Oct 26 2019 Main focus continues to be on rain coverage and amounts through early tonight. Rain has already moved into the southern CWA early this morning and will continue to spread north across the CWA throughout the rest the morning. This is occurring as deep upper low currently over the Red River Valley will deepen as it moves across Missouri and Illinois late this afternoon into this evening. Surface low currently along the Gulf Coast will move north into east central Illinois by this evening and also quickly strengthen. It still looks like that CWA is set up for a favorable rain event with deformation zone of the upper low moving over the CWA at the same time strong moisture transport will be bringing around 1.5" PWATS into the area. With this in mind, will keep categorical PoPs over almost the entire CWA with total storm amounts ranging from around less than 0.25" in the northwest to around 2.5" in eastern CWA. Forecast mid level lapse rates will also be near 7 C/km, so will leave isolated thunderstorms in the forecast. GFS/NAM are in reasonable agreement that the upper low will lift into southern Lake Michigan by tonight and shortwave ridge will move into the area tomorrow. This is consistent with rain moving out of the region this evening and the area being dry late tonight into Sunday. Temperatures today will be held down by the clouds and the widespread rain. Highs on Sunday will climb back into the 60s with sunshine and southerly winds. Britt .LONG TERM... (Sunday Night through Friday) Issued at 313 AM CDT Sat Oct 26 2019 Main concern through next week will be the potential for additional precipitation chances as a long wave trough digs into the central CONUS. CIPS analogs continue to show surface temperatures between 10-15 degrees below normal by mid-late next week. Yet there is still some uncertainty as the operational ECMWF is slower than the GFS in how quickly it moves an upper low into the central CONUS next week. In addition, while the GEFS plumes agree that temperatures will fall behind a cold front that will move slowly across the area Monday into Tuesday, there remains considerable uncertainty regarding the details in precipitation timing. In addition, the GEFS mean temperatures are lower than the operation mean. With that said, it still looks like the first round of rain just behind the front late Monday into early Tuesday as a weak shortwave trough moves northeast across the Midwest. The next chance of precipitation will then come with the approach of the upper low Tuesday night into Thursday. Thermal fields from the various models and the GEFS plumes support keeping a rain/snow mix over the northern and western parts of the CWA with this event. Model uncertainty remains on how quickly this system will exit the area, but the GEFS are favoring a quicker motion, so will leave Friday dry for now. Britt && .AVIATION... (For the 06z TAFs through 06z Saturday Night) Issued at 1039 PM CDT Fri Oct 25 2019 Confidence remains high that rain, reduced visibilites, and low cigs will move into the region on Saturday morning, though latest guidance has slowed the arrival time a bit compared to the afternoon runs. Models still depict a rapid drop from VFR into IFR cigs at the STL terminals as the rain arrives in the mid morning. Some signal remains showing LIFR cigs near STL, but confidence on this remains low, so have just continued the SCT003 mention for the time being. Cigs are expected to remain above 1000 kt at UIN and especially COU, which are both further removed from the weather system responsible for these reduced conditions. The biggest uncertainty with this forecast is how quickly conditions will improve on Saturday evening. There is fairly overwhelming model consensus showing dry air rapidly filtering into the area after 00z, helping to quickly get rid of the sub-VFR conditions. However, the evening and overnight hours in the cool season are not when we typically see rapid cloud dissipation, so I'm a little hesitant to fully buy into the model solution. I am therefore holding onto MVFR cigs a bit longer than the models suggest at all sites. Additionally, I've kept SCT025 through the end of the TAFs at COU and STL to signal some chance for MVFR cigs through the end of the TAF period. BSH && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX