FXUS63 KLSX 091038 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 538 AM CDT Fri May 9 2025 .KEY MESSAGES... - Temperatures will warm through the weekend into next week. - The weekend is expected to be dry, with multiple periods of active weather expected next week. && .SHORT TERM... (Through Saturday Night) Issued at 226 AM CDT Fri May 9 2025 Early morning water vapor imagery shows that the axis of an upper- level trough is pivoting through the Great Lakes, with an upper low becoming sheared out across the Ohio and Middle Mississippi vallies. A weak cold front is sinking southward through the region, with an expansive area of high pressure spreading across the Midwest in its wake. This high and cooling temperatures aloft will lead to a pleasant day across the CWA, with temperatures this afternoon (low 70s) running cool for early May this afternoon. Saturday, a Rex Block will begin forming across the central CONUS, and the area of high pressure at the surface expands further across the Midwest and Northeast. This will keep our weather calm, though temperatures will warm over what is expected today as the cooler pocket of mid-level temperatures shifts eastward. Warming mid-level temperatures and ample sunshine will help temperatures warm 5-10 degrees compared to Friday, with most locations seeing afternoon values in the mid 70s up to 80 degrees. Elmore && .LONG TERM... (Sunday through Thursday) Issued at 226 AM CDT Fri May 9 2025 On Sunday, guidance consensus is that the Rex Block will have fully taken hold over the central CONUS. This and high pressure anchored over the Great Lakes at the surface is expected to keep our weather mild and dry through Sunday. Confidence is high that this calm weather will be short lived, as a majority of guidance has the upper low over the Lower Mississippi Valley drifting northward into the Ohio Valley and Great Lakes Monday into Tuesday. While deterministic guidance and ensemble clusters show varying degrees of phasing of this feature, the majority have the enhanced upper-level forcing and moisture displaced eastward of the CWA. The result is low to medium (30-60%) chances of rain mainly focused over eastern/southeastern portions of the CWA, with the greater probabilities remaining eastward. Any rainfall that occurs is expected to generally be light, with ensemble probabilities for 0.10" topping out around 30- 40% across southeastern Missouri and southwestern Illinois. As the low continues to move north-northeastward, upper-level southwesterly flow will become increasingly established over the CWA Wednesday toward the end of the workweek. This will initiate a several-day period of robust warm air advection, with forecasted mid- level temperatures from ensembles running at the 99th percentile of climatology by Thursday, climatologically favoring surface temperatures in the mid to upper 80s. An upper-level trough pivoting from the Intermountain West into the Northern Plains per ensemble majority on Friday will swing a cold front through the Midwest late Thursday or Friday. The post-frontal air mass will be weak and cold air advection meager, so a drastic drop in temperatures is not expected, and ensemble means drop only by a couple of degrees into next weekend. Elmore && .AVIATION... (For the 12z TAFs through 12z Saturday Morning) Issued at 537 AM CDT Fri May 9 2025 Confidence is high in dry and VFR flight conditions at all local terminals through the forecast period, with northeasterly winds remaining light to variable. Elmore && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX